3HP 220 V motors - 20 amp or 30 amp circuits?

[Mike Williams]

My new shop is finally under construction http://www.sawmillcreek.org/images/icons/icon7.gif, and the electrician should be showing up in about a week to start the wiring. I have a question on the wiring and circuit breaker size for 3 HP motors.

I will have individual 220V circuits for all of the heavier machines (air compressor, dust collector, lathe, tablesaw, bandsaw and planer). Each of these will be 3 HP motors.

None of the wiring runs will exceed 50 feet from the 200 amp sub-panel.

The best information I can find says I should size the circuit based on a 3 HP motor drawing 17 amps, and sizing the circuit for 125% of the load. That would mean each of these circuits should be sized for 21.2 amps. This means a 30 amp circuit and 10 gauge wiring.

Does that sound right? My gut feeling is a 20 amp circuit with 12 gauge wire would be ok. Are there any of the above machines that should definitely be on a 30 amp circuit?

Thanks, Mike

[Eddie Darby]

I would like to point out that there may be an advantage in having at least one circuit that will handle a heavier load, this way if you ever up-grade to a more powerful machine, you will be ready for it.

[Von Bickley]

The 3 HP cabinet saws that I have had experience with were wired with #12 wire on double 20 amp breakers.

Worked fine on these saws....:)

[Mike Cutler]

Mike.
I'm sure you'll recieve a lot of replies and opinions. In the end you'll install the breaker that the inspector wants to see there. I know that's a "crappy" answer, but there it is
The local licsense should know what the inspector wants to see.
A 20 amp breaker wit 12/2 will do it, but I'll be surprised if you don't end up running #10awg, and installing a 30 amp breaker.
The "heaviest loads" I see in your list is the dust collector, and the planer. A bandsaw resawing draws significant current also. They all have 3 hp motors, so I would expect them to all be treated equally.

[Robert Waddell]

After having two shops wired and two differ electricans, my answer would be #12 wire and 20amp breakers.
Rob

[Jim Fox]

My 3hp Cabinet Saw was run on a 30amp breaker in the old house, can't recall the wiring, think it was 10 gauge.

Just wired up the new shop and my electrician buddy told me 10 gauge. So, now the 3hp Cabinet Saw and ShopFox 1741 jointer are on 10 gauge runs, both 30 amp breakers.

[Tom Veatch]

A 20 amp breaker is all you'd ever need for a 220v 3HP motor. It wouldn't hurt anything to run 30amp circuits if you so choose, but it's overkill. 12 ga 2 conductor with ground would be my choice for wire unless there's an extraordinalily long wire run from the box to the outlet.

Unless you're going to hardwire them as as a dedicated circuit, you'll run the wire to one (NEMA 6-20 (http://www.westernextralite.com/resources.asp?key=69)) or more wall outlets (NEMA 6-20 or NEMA 6-15) and the inspector would never see what's plugged into the outlet(s). And since these aren't continuous duty applications, the 125% upsizing isn't required.

I can't imagine requiring more than a 20 amp circuit to satisify a 3HP intermittent load (appx 12 - 15 FLA and much less than that on average). But, if you do decide to overkill it and go with 30 amp branch circuits, even for the 3HP machines, you'll need NEMA 6-30 outlets, and, in any case, a matching plug on the equipment.

I would suggest that you do use 30 amp/10 ga circuits for the Dust Collector and Air Compressor circuits. If you're going to upsize any of the things you mentioned to 5HP, my guess is those will be the ones. Unless you're looking toward becoming a serious production shop, 3HP woodworking machines are plenty big enough.

All the above, notwithstanding, my advice is to tell your electrician the intended use of the circuits and let him/her install what he/she knows is appropriate and will pass inspection.

[Rick Gifford]

My 3HP 220V motor is rated for 18 amps. So a 20 Amp breaker and 12 AWG wire is all that is needed.

[Gary Curtis]

My 5hp saw draws 19 amps. General of Canada told me when I bought it that the motor simply would not trip even a 20-amp circuit breaker. So, what does that tell you?

Gary Curtis

[Ken Fitzgerald]

Mike,

I ran 10 gauge wire and installed 30 amp breakers on all 8 of my 220 circuits. The difference in wire cost is negligible compared to the problems running it later. The breaker is really protecting the wire not the machine.
Thus if you run 12 gauge copper, use a 20 amp breaker.

Your electrician should know what will meet your local inspector's expectations.

[Steve Rowe]

When I built my shop, I wanted no electrical limitations for what I could potentially have in the future. There is no difference in cost between 20amp and 30 amp breakers. The only difference you would see is the relatively minor difference in cost between 10 gauge and 12 gauge wire. At the time of building the shop, 20 amp circuits would have satisfied my needs at the time. Now, 17 years later with several machine upgrades, I would have had to rewire my shop for larger circuits. Glad I went with 30 amp circuits.
Steve

[dave rollins]

Mike
Would you give us a little more info on your new shop?

1. Is this a separate new structure and if so has the concrete slab been poured?
2. Are you running the wiring in romex in the walls?

The reason I ask the questions is that if you haven't poured the slab yet you have a number of options open to you. If you are running the wiring in the walls then at least run 10 ga. and for now I would put them on a 20 amp breaker. I would only put a 30 amp breaker on these circuits if the manufacturer recommends this.
These suggestions come from being in the electrical construction industry for close to 30 yrs. and also from someone who has had to redo their own shop.
I hope this helps
DAVE

[Jason Beam]

While 20a wiring MIGHT work. 30a WILL work for sure, plus you'd have room to bump up to a bigger tool later.

The compressor's your highest amp drawing tool, for sure. The dust collector might pull some heavy amps when you have it moving it's maximum air. The planer might pull some amps when you're taking a deep cut on wide stuff. But most of the time, none of the other tools will draw full amperage under normal use like the compressor will.

Startup current is going to be your biggest draw, for sure. Especially on that compressor. Those things can pull a TON of amps for a full second or more (beyond the slow-blow threshold sometimes).

Wire for more than you need. You'll be glad you did the day a tool gets upgraded. You'll kick yourself if your 20a breakers pop in the winter when that compressor's cold.

Second option: run 10ga wire but put in 20a breakers and upgrade if need be. That's a little more cost effective. It's easy to upgrade a breaker. Not so much the wire.

[Tom Godley]

Here we go again!!

I am new to this forum and I very much like reading all the posts - many, have been a great help to me as I try to put my new shop together.

But, I must say that I have read too many posts regarding electrical issues that are not accurate - or better said not quite accurate.

From a safety "point of view" there is no direct problem with installing #10 or even #8 wire and then installing a breaker with a lower Amp rating -- say 20amp. We would not allow this in our factory on a rewire.

What some people do not understand is that 30A 240V is a lot of power- and it can kill you -- as well as allow a situation to develope that can very easily create a fire.

If a tool only requires a 20 amp line -- install a good 20amp breaker - you gain nothing having a 30 amp breaker on that tool.


sorry to preach

[glenn bradley]

You'll get mixed replies on this one. 3HP saws seem to generally recommend 20a and 12ga. Grizzly recommends a 30a for their 3HP (18a) jointer (via email) and Penn State recommends the same for their 3HP DC.

I ran 10ga to my 20a positions. That way if I want to go higher, I just change the breaker and outlet.

P.s. Tom, preach away ;-)

[Ken Fitzgerald]

Here we go again!!

I am new to this forum and I very much like reading all the posts - many, have been a great help to me as I try to put my new shop together.

But, I must say that I have read too many posts regarding electrical issues that are not accurate - or better said not quite accurate.

From a safety "point of view" there is no direct problem with installing #10 or even #8 wire and then installing a breaker with a lower Amp rating -- say 20amp. We would not allow this in our factory on a rewire.

What some people do not understand is that 30A 240V is a lot of power- and it can kill you -- as well as allow a situation to develope that can very easily create a fire.

If a tool only requires a 20 amp line -- install a good 20amp breaker - you gain nothing having a 30 amp breaker on that tool.


sorry to preach

Tom.......I've been working on x-ray equipment, MR scanners, Ct scanner for 31 years and I started working on radar and communications equipment used in air traffic control centersin 1970. Annually I have to take electrical safety courses via my company's EHS plan.

It's the current that kills you....milliamps are enough to kill you.......so 20 amps or 30 amps it really doesn't matter from a personal protection standpoint.

You can run 20 amp breakers and 10 gauge wire.......20 amp breakers and 12 gauge.......or you can buy one 30 amp breaker and use 10 gauge....the circuit breaker is there to protect the wire and prevent fire ....not protect you or the machine.

[Tom Godley]

Ken - I do understand what you are talking about - and i value your knowledge on the subject.

But -many tools being purchased and installed in home shops do not have cords or internal parts that allow them to be attached to a 30 amp breaker in a safe maner. Most importantly they do not need to be.

As parts age - cords especially - they become vulnerable. Add to this the phsical damage that the cord may take from something falling on it in a shop and you have a disaster waiting to happen.

The circuit is an electric system- you want all the parts to work together to make the system safe. The breaker "is" there to protect you and the machine - you have to allow it to be able to do its job.


Oh My -- well past my bed time on the east coast -- I have shop planning to to tomorrow

[Rick Christopherson]

It really irritates me reading some of the misinformation presented in this thread that is passed off as knowledgeable advice. The original poster asked what was required and only a couple of people appear to be qualified to answer this.

A 3 hp motor does not need any more than a 20-amp circuit with #12 wire (and Grizzly is not a valid source of information). Many 3 hp motors can even be run legally on 15 amp circuits, but this is not something I would recommend on a new installation. As was pointed out, most of these tools are not continuous duty, nor continuous load, so the 125% rule is not applicable.

It is fine to suggest that a person install #10 wire to plan ahead, but half of the responses stating this are just knee-jerk responses without much forethought. These posters make it sound as though it is a common everyday situation of upgrading to a 5 hp tool, when the chances are actually much narrower. The need for this is on a person to person basis, but these posters make it sound like every shop will have loads of 5 hp tools. As one person pointed out, a dust collector and compressor are the most common exceptions where a small shop might have 5 hp tools.

[Mike Williams]

Thanks to all of you for your responses. I realized from past posts on similar topics that there would be some different points of view.

My first step will be talk to the electrician when he shows up and take his advice. Unless guided differently, I'll plan on the 20 amp / 12 gauge circuits.

The building is a new free-standing structure with a full basement underneath. I wanted wood floors, and my wife wanted the basement storage space, so we are both going to be happy. That makes it fairly easy to pull a new circuit in the future if required.

I can't foresee going to a 5 HP motor in the future. It's a bigger tool than I believe I will ever use, and my local electric company has imposed a 3 HP limit on any individual motor in the shop. The utility company is ok with the change at the house from 200 amp to 400 amp, but they don't want the instantaneous draw of a 5 HP motor (something about dimming the lights at the neighbors!). Seems to me like the utility company's wires at my property line won't know whether a 5 HP motor turned on, or two 3 HP motors turned on simultaneously, but that's their position.

[Ken Fitzgerald]

It really irritates me reading some of the misinformation presented in this thread that is passed off as knowledgeable advice. The original poster asked what was required and only a couple of people appear to be qualified to answer this.

A 3 hp motor does not need any more than a 20-amp circuit with #12 wire (and Grizzly is not a valid source of information). Many 3 hp motors can even be run legally on 15 amp circuits, but this is not something I would recommend on a new installation. As was pointed out, most of these tools are not continuous duty, nor continuous load, so the 125% rule is not applicable.

It is fine to suggest that a person install #10 wire to plan ahead, but half of the responses stating this are just knee-jerk responses without much forethought. These posters make it sound as though it is a common everyday situation of upgrading to a 5 hp tool, when the chances are actually much narrower. The need for this is on a person to person basis, but these posters make it sound like every shop will have loads of 5 hp tools. As one person pointed out, a dust collector and compressor are the most common exceptions where a small shop might have 5 hp tools.

Rick,

I am caulking and should start painting the east half of my shop this weekend and then the shop is finally finished.

IF I hadn't run 10 gauge, either I'd be ripping the plywood off the walls to gain access to the electricals or I'd be running external conduit to run 10 gauge copper for the Mini-Max MM-16 4.8 hp bandsaw sitting in the crate in the shop waiting for the shop to be finished. I never thought I'd have that much h/p in one machine but I do now.

The 10 gauge runs to all 8 of my 220 circuits allow me to use that bandsaw at any of the 8 220 outlets in the room. They also give me some leaway in where to place the Onieda D/C I'll be ordering later this month. I don't think putting in 10 gauge is "knee jerk" reaction any more than buying life insurance is a "knee jerk" reaction.

I answered Mike's queston with the last statement in my first response "Thus if you run 12 gauge, use a 20 amp breaker. Your electrician should know what will meet your local inspector's expectations."

Respectfully,

[Steve Rowe]

Ken - I do understand what you are talking about - and i value your knowledge on the subject.

But -many tools being purchased and installed in home shops do not have cords or internal parts that allow them to be attached to a 30 amp breaker in a safe maner. Most importantly they do not need to be.

As parts age - cords especially - they become vulnerable. Add to this the phsical damage that the cord may take from something falling on it in a shop and you have a disaster waiting to happen.

The circuit is an electric system- you want all the parts to work together to make the system safe. The breaker "is" there to protect you and the machine - you have to allow it to be able to do its job.


Oh My -- well past my bed time on the east coast -- I have shop planning to to tomorrow
Tom,
With all due respect, Ken is correct, the circuit breaker is sized to protect the wiring. The size of the breaker is generally determined by the wire size, wire material, length, and type of insulation. The requirements for this are specified by the NEC and local building codes. Unless the circuit breaker is a GFCI, it does not protect you. Unless you have protective relaying in your switchgear, the circuit breaker does not protect the load beyond what exists for wiring protection. That is why motors typically have thermal overload protection built into them - this is what protects the motor.

Rick,
Your "knee jerk reaction" and "narrow chances" comments are your opinion. One would hope that lessons learned from the experiences of others on this forum would be better received by those who profess to be more knowledgable. Potential future machine upgrades within reason are just one of those considerations and is pretty much a common sense question. As I indicated in my previous post, when I built my shop 20 amp circuits were sufficient. I have made several machine upgrades and based on my shop layout, I would have had to rip out 30 feet of sheetrock to replace wiring to handle a 30 amp circuit or go surface mount. The decision whether to upgrade and when is always up to the end user.

Mike,
I have no idea how your utility company can specify a load limit of 3HP. You either have 200 amp service or you do not. If the 3HP is a true limit, I would question whether you really have 200 amp service. Honestly, the limit sounds like a bunch of hooey to me and I work for a utility as a design engineer in the power generation end of the business.

Steve

[Jim O'Dell]

I'm another one that ran 10 guage wiring and 30 amp breakers for all 8 of my 220 outlets. The only one that needs it now is the cyclone. Hopefully a cab saw and big compressor is in my future that will also require it. Probably should have run 8 to the point I'll hook up the little welder, but 10 is probably plenty safe for it. it's a small unit, and I haven't even used it yet.
Another thing to consider, if running a lower amp tool on a 30 amp breaker causes no problems, I've seen no difference in price between the 20 amp and 30 amp breakers. The all sold for the same price. Jim.

[glenn bradley]

It really irritates me reading some of the misinformation presented in this thread that is passed off as knowledgeable advice. The original poster asked what was required and only a couple of people appear to be qualified to answer this.

A 3 hp motor does not need any more than a 20-amp circuit with #12 wire (and Grizzly is not a valid source of information). Many 3 hp motors can even be run legally on 15 amp circuits, but this is not something I would recommend on a new installation. As was pointed out, most of these tools are not continuous duty, nor continuous load, so the 125% rule is not applicable.

It is fine to suggest that a person install #10 wire to plan ahead, but half of the responses stating this are just knee-jerk responses without much forethought. These posters make it sound as though it is a common everyday situation of upgrading to a 5 hp tool, when the chances are actually much narrower. The need for this is on a person to person basis, but these posters make it sound like every shop will have loads of 5 hp tools. As one person pointed out, a dust collector and compressor are the most common exceptions where a small shop might have 5 hp tools.

Rick makes a good point and the need to build for growth will vary with each person. I chose to go with larger gauge wire to avoid ever having to drywall again (which I hate). If I was staying with open studs I would have possibly done different. I run appropriate breakers and outlets and probably fool myself that if I do want to upgrade breakers and outlets that the outlet position will be appropriate for my future needs . . . but I can dream.

[Ken Fitzgerald]

I'm another one that ran 10 guage wiring and 30 amp breakers for all 8 of my 220 outlets. The only one that needs it now is the cyclone. Hopefully a cab saw and big compressor is in my future that will also require it. Probably should have run 8 to the point I'll hook up the little welder, but 10 is probably plenty safe for it. it's a small unit, and I haven't even used it yet.
Another thing to consider, if running a lower amp tool on a 30 amp breaker causes no problems, I've seen no difference in price between the 20 amp and 30 amp breakers. The all sold for the same price. Jim.

Jim....there's a bigger a/c in my future too! That's another reason I ran 10 gauge.

[Tom Veatch]

...Another thing to consider, if running a lower amp tool on a 30 amp breaker causes no problems,...

Jim, the emphasis on the "if" in your statement implies a concern. Responding to that, I'll simply mention that I doubt anyone has misgivings about plugging a 5 amp saber saw into a 15 or 20 amp circuit. Likewise, there should be no misgivings about plugging a 15 amp table saw into a 30 amp circuit. The same physics apply in either case.

But, just as you don't NEED a 20 amp circuit run the saber saw, neither do you NEED a 30 amp circuit to run the table saw.

[M Toupin]

I must say that I have read too many posts regarding electrical issues that are not accurate - or better said not quite accurate.

Exactly...



What some people do not understand is that 30A 240V is a lot of power- and it can kill you -- as well as allow a situation to develope that can very easily create a fire.

Tom, with all due respect, 20A is just as dangerous as 30A and will kill you just as quick and just as dead under the proper circumstances. It really doesn't take much at all. At 110/220V, 50 or 60Hz AC can cause ventricular fibrillation at currents as low as 60mA. With DC power ventricular fibrillation can occur at 300 to 500 mA. So you see, weather it's 20A or 30A it's well over the threshold by a HUGE factor. 20A is no safer than 30A.

Mike, as far as circuits it sounds like 20A/12ga circuits would be fine for your present needs. You might want to consider any possibility that you might want to upgrade in the future though. Personally I would run 10ga if I was in your shoes, but that's just me. Most of us suffer from the Tim Taylor syndrome in that we like "more power!":D and our machines keep getting bigger and more powerful. Another thing I haven't seen mentioned is you might also consider a 50A circuit if you think you might have a need for an arc welder in the future. I have a 50A circuit wired next to the door for just that purpose. That way I can drag the arc welder outside and not worry about a fire in the garage.

Mike

[Rick Christopherson]

I didn’t say that upgrades don’t happen or can't happen, but the original poster wasn’t asking this. He was asking what was required for a 3 hp motor. In response, one person stated that an electrician told him 30 amp was required. Another person implied that a state inspector would force him to use 30 amp circuits. Steve stated that many of his tools have been upgraded and needed the 30 amp circuits, but didn’t tell us what these tools were that needed 30 amps. I’m not saying that these tools don’t need 30 amps, but I have also seen this same type of statement repeated dozens of times in the past, only to learn later that upgrades still didn’t require 30 amps. Of all the people that suggested 30 amp circuits, not one of them indicated that NEMA 6-30 outlets are required, and I believe at least one person even stated that he used 20 amp outlets on the 30 amp circuit. (Tom correctly stated this, and his response was one of the best in the whole discussion.)

I am a strong advocate of planning ahead, and one aspect of that sometimes means oversizing an existing circuit. Blindly installing 30 amp circuits everywhere for every workshop is not planning at all, it is just blind overkill. If you have a workshop that is physically large enough to support large tools, then using larger circuits is a good idea. However, I have seen this same advice given to people with a 10x20 workshop, and they could barely shoehorn a standard tablesaw into the shop.

Some of you took offense with my use of “knee-jerk responses”, yet only one person bothered to ask the original poster any information about his workshop, and no one bothered to ask how the shop was used or laid out. The original poster specifically stated that he was using all 3 hp machines, but many of you completely overlooked that. That is by definition, knee-jerk.

Knee-jerk: reacting according to a certain habitual manner; unthinking.

Every time this topic comes up, people always have justifications of why this was applicable in their shop, and therefore it must be applicable to all shops. Well it’s not applicable to all shops or all tools, so automatically advising every poster that this is what they should do in all situations is just blind advice. Some tools are a lifetime investment and will never need to be upgraded. Some tools have specific infeed and outfeed requirements, so can never be relocated and still meet those requirements. But all of these responses overlook these possibilities.

The biggest problem is that this information gets repeated so much by so many people that it has become a standard response (a.k.a. knee-jerk) for all situations, and nobody bothers to take the time to identify when it is applicable and when it is not. After getting bombarded with this so much, other woodworkers begin to see it as though it was a requirement. No, there is nothing wrong with installing #10 wire, but in some cases, there is nothing gained by it either. I don't oppose installing 30-amp circuits (or at least #10 wire) but what I do oppose is the blind advice that this needs to be done in all situations.

[Ken Fitzgerald]

Another thing I haven't seen mentioned is you might also consider a 50A circuit if you think you might have a need for an arc welder in the future. I have a 50A circuit wired next to the door for just that purpose. That way I can drag the arc welder outside and not worry about a fire in the garage.

Mike

M toupin,

I did just that. My 200 amp service box is between the 48" walkin door and the insulated 10' garage door. One circuit left open for a 50 amp breaker and the plywood below the breaker box is screwed on in such a way as it can be removed....a 50 amp box and outlet installed and take the welder outside.

[Pete Bradley]

Rick,
Your "knee jerk reaction" and "narrow chances" comments are your opinion. One would hope that lessons learned from the experiences of others on this forum would be better received by those who profess to be more knowledgable.
Steve

I agree with the desire to see posts based on lessons learned and experience. Rick's comment was that a lot of the responses were knee-jerk, not that 30A was. Certain topics routinely get answers where people who have no personal experience or knowledge beyond previously having seen an answer on the internet immediately regurgitate what they've read. This adds no value and often propagates bogus "internet wisdom".

Pete

[SCOTT ANDREWS]

[. No, there is nothing wrong with installing #10 wire, but in some cases, there is nothing gained by it either. I don't oppose installing 30-amp circuits (or at least #10 wire)

THEN WHAT'S YOUR PROBLEM

[Steve Rowe]

I didn’t say that upgrades don’t happen or can't happen, but the original poster wasn’t asking this. He was asking what was required for a 3 hp motor. In response, one person stated that an electrician told him 30 amp was required. Another person implied that a state inspector would force him to use 30 amp circuits. Steve stated that many of his tools have been upgraded and needed the 30 amp circuits, but didn’t tell us what these tools were that needed 30 amps. I’m not saying that these tools don’t need 30 amps, but I have also seen this same type of statement repeated dozens of times in the past, only to learn later that upgrades still didn’t require 30 amps. Of all the people that suggested 30 amp circuits, not one of them indicated that NEMA 6-30 outlets are required, and I believe at least one person even stated that he used 20 amp outlets on the 30 amp circuit. (Tom correctly stated this, and his response was one of the best in the whole discussion.)

I am a strong advocate of planning ahead, and one aspect of that sometimes means oversizing an existing circuit. Blindly installing 30 amp circuits everywhere for every workshop is not planning at all, it is just blind overkill. If you have a workshop that is physically large enough to support large tools, then using larger circuits is a good idea. However, I have seen this same advice given to people with a 10x20 workshop, and they could barely shoehorn a standard tablesaw into the shop.

Some of you took offense with my use of “knee-jerk responses”, yet only one person bothered to ask the original poster any information about his workshop, and no one bothered to ask how the shop was used or laid out. The original poster specifically stated that he was using all 3 hp machines, but many of you completely overlooked that. That is by definition, knee-jerk.

Knee-jerk: reacting according to a certain habitual manner; unthinking.

Every time this topic comes up, people always have justifications of why this was applicable in their shop, and therefore it must be applicable to all shops. Well it’s not applicable to all shops or all tools, so automatically advising every poster that this is what they should do in all situations is just blind advice. Some tools are a lifetime investment and will never need to be upgraded. Some tools have specific infeed and outfeed requirements, so can never be relocated and still meet those requirements. But all of these responses overlook these possibilities.

The biggest problem is that this information gets repeated so much by so many people that it has become a standard response (a.k.a. knee-jerk) for all situations, and nobody bothers to take the time to identify when it is applicable and when it is not. After getting bombarded with this so much, other woodworkers begin to see it as though it was a requirement. No, there is nothing wrong with installing #10 wire, but in some cases, there is nothing gained by it either. I don't oppose installing 30-amp circuits (or at least #10 wire) but what I do oppose is the blind advice that this needs to be done in all situations.


After a couple of "serenity now's", I am somewhat reluctant to respond to this post. This is my last post on this thread as I will not get into nit-picking arguments over minutia. I don't feel the need nor any obligation to justify circuit sizing or the machinery in my shop. Suffice it to say, 5HP machine nameplates specifying FLA of 23 amps at 230VAC at a power factor of 0.88 require more than a 20 amp circuit. I consult licensed PEs and refer to the NEC when doing electrical work in my shop. You appear to have the approach: "If the minimum wasn't good enough, it wouldn't be the minimum." Well, that is an approach. I for one, actually prefer having some design margin for flexibility.

Use of 30 amp outlets unless you hardwire, is a statement of the obvious for 30 amp loads. In addition, don't put a 100 watt bulb in a 60 watt fixture - also a statement of the obvious. The list could go on infinitum. Some things are so obvious they just shouldn't have to be stated.

Regarding the "knee jerk" comment, thank you for the definition and your stated opinion about those of us who don't happen to be a source of infinite knowledge.

I do agree there is a lot of bum information on this and other forums regarding electrical topics and several others. The bottom line - if you are not paying for the advice from licensed professionals, you are getting exactly what you paid for.

[Rod Sheridan]

I'm not sure why we end up in this quagmire every time someone posts about what size circuit to use for a 3HP motor except for;

1) the circuit sizing will depend upon the individual 3 HP motor. A high quality 3 HP motor will have a full load current in the 12 ampere range.

A low quality (low power factor and low efficiency) 3HP may have a full load current in the 19 ampere range.

2) The intended use of the motor (i.e. duty cycle, load factor).

Many 3 HP motors will conform to the 80% rule with 15 ampere circuit protection, some will require 20 or 30 ampere circuit protection.

Yes, all 3 HP motors between 12 and 24 amperes will meet the 80% rule on a 30 ampere circuit, however good engineering practice dictates that each situation be evaluated.

Thus, there will be different solutions based upon the individual piece of equipment.

Regards, Rod.

[Rick Christopherson]

Many 3 HP motors will conform to the 80% rule with 15 ampere circuit protection, some will require 20 or 30 ampere circuit protection.Rod, I agree with everything you said, with the exception of the 80% derating information. The 80% derating is required for continuous loads, and most home woodworking equipment does not fall into this classification. If the equipment is not continuous, then the circuit does not need to be derated.

Not only is the duty cycle not continuous, but the load cycle is also very low. A tablesaw is a good example: The saw runs at sporadic intervals. Even when the saw is running, much of this time is at no-load, and even in use, is only at 75-80% load, with rare excursions into the full-load range.

The most notable exceptions for woodworking machines are dust collectors and compressors. These operate at full load while they are running, so the only aspect open for interpretation is the duty cycle, and this is Dependant on the habits and usage for the individual.

[Rod Sheridan]

Rick, I have previously replied to your past posts regarding the 80% rule.

As I have previously stated, it is unethical for me to provide engineering services without investigating the operating conditions at the particular site.

The 80% rule covers all possible operating conditions, to use another method of circuit sizing without investigation is unethical, and contrary to professional standards.

You may feel comfortable with the assumptions you've made, I am not.

Hence the 80% rule will be used by me, since I have to exercise due diligence.

Your professional circumstances may dictate otherwise.

regards, Rod.

[Rick Christopherson]

Rod, Due diligence goes both ways. Under what possible circumstances could a home tablesaw run with a 100% duty cycle and Load cycle? Not even with a power feeder is this reasonably expected in a home workshop.
.... it is unethical for me to provide engineering services without investigating the operating conditions at the particular site.But you just did provide advice without a full investigation. :mad:

[Chris Friesen]

The 80% derating is required for continuous loads, and most home woodworking equipment does not fall into this classification. If the equipment is not continuous, then the circuit does not need to be derated.

This is something that has confused me about the code.

430.22(A) says that continuous duty applications mean that the conductors need an ampacity of at least 125% of the FLA.

430.22(E) Says that conductors for motors used for short-term, intermittent, periodic, or varying duty should use the percentages in table 430.22(E). However, according to that table if the motor itself is continuous-load rated (even if it's not being used in a continuous manner) that table specifies at least 140% of the FLA, and for "varying duty" it specifies 200% of the FLA!

By my reading, with a continuous duty rated motor (which most woodworking equipment uses) you're better off treating it as a continuous duty application and using the 125% value.

I'd love to know where I'm going wrong in my reasoning, cause it just doesn't make sense to me.

[Rod Sheridan]

Rod, Due diligence goes both ways. Under what possible circumstances could a home tablesaw run with a 100% duty cycle and Load cycle? Not even with a power feeder is this reasonably expected in a home workshop.But you just did provide advice without a full investigation. :mad:


Yes I did, however I provided a solution that will meet all uses of the device in compliance with code requirements.

No authority or inspector will challenge your use of the 80% rule, as opposed to proof of load factors or duty cycle.

Proof is required to use other rules, and as I don't have any proof of the intended use, I've reccomended the 100% fool proof method.......Rod.

[Rod Peterson]

...I provided a solution that will meet all uses of the device in compliance with code requirements.

No authority or inspector will challenge your use of the 80% rule, as opposed to proof of load factors or duty cycle.

Proof is required to use other rules, and as I don't have any proof of the intended use, I've reccomended the 100% fool proof method.

[some snippage and some concatenation from another post]

As I have previously stated, it is unethical for me to provide engineering services without investigating the operating conditions at the particular site.

The 80% rule covers all possible operating conditions, to use another method of circuit sizing without investigation is unethical, and contrary to professional standards.

You may feel comfortable with the assumptions you've made, I am not.

Hence the 80% rule will be used by me, since I have to exercise due diligence.

I have to ask, then, why are you here? People come to these fora looking for solutions to their problems. They come to them expecting to hear from people who really know what they're talking about. The high standard, in my opinion, of such an enterprise is the John Bridge forum for all things related to tile.

Imagine if someone asked at John Bridge how to tile a backsplash over a kitchen counter and all the professionals (in all their ethical restraint) recommended a complete mud job and/or cement backer board, porcelain tile, and epoxy grout. It certainly would meet every possible requirement, but it's at least a bit more than reasonable or necessary.

To bring it back to woodworking, to answer the question, for example, "what table saw should I get?" with, "an Acme 14" with power feeder, dual dipsticks, and high speed hubcaps," simply because that answer will "cover all possible operating conditions," is no less irresponsible for a professional (and a greater waste of time) than to either conduct the investigation you feel so strongly (and probably correctly) is necessary and give a more productive answer, or not answer at all.

Paraphrase though the saw example may be, that represents precisely your stated philosophy regarding the OP's situation. If you truly feel your professional existence is potentially at peril by offering anything other than the "biggest-size-fits-everyone" solution in an area where your expertise could be of great value, why not just stick to advising on something you know nothing about. Frankly, it wouldn't be any less useful.

[Luis Oliveira]

If my limited experience is any guidance, I have found that once you have 3HP machines you will soon start looking at 5HP machines, especially drum sanders, DC, and so on... so If it was me, will install at least 2 - 30A, 4-6 220 20A, and 6 120 20A. I will let more savy people tell you the gauge of the actual wire...

[Mike Seals]

Rick, I have previously replied to your past posts regarding the 80% rule.

As I have previously stated, it is unethical for me to provide engineering services without investigating the operating conditions at the particular site.

The 80% rule covers all possible operating conditions, to use another method of circuit sizing without investigation is unethical, and contrary to professional standards.

You may feel comfortable with the assumptions you've made, I am not.

Hence the 80% rule will be used by me, since I have to exercise due diligence.

Your professional circumstances may dictate otherwise.

regards, Rod.

80% rule, err on the side of safety.

[Rick Christopherson]

I have to ask, then, why are you here? Rod (Peterson), You took the words right out of my mouth, except your analogy was better than the one I was thinking about using. :)

To say that he is providing this misinformation because it is the ethical thing to do is very much incorrect. It is equally unethical to provide false information, regardless whether it was overstated or understated advice, especially when this misinformation is in lieu of performing a proper analysis or applying known conditions (such as those I already commented on).

The proponents of the overuse of this 80% derating rule typically make it sound as though they do so as a safety concern, when it is not, and nothing irritates me more than misapplied scare tactics. There are many different reasons where a circuit needs to be derated for safety, the most notable is for temperature, but this particular derating is not safety related per se. If it was safety related, then all electrical circuits would have to be derated as well.

I don’t know to what level an Electrical Technologist’s education goes, but I do know it is not to the same level as an Electrical Engineer, because a technologist answers to an engineer. As an Electrical Engineer, it would be my task to design a circuit to meet the needs of the circuit, and as part of this design, determine whether oversizing the circuit was applicable, desired, or not relevant. To blindly oversize a circuit without evaluating the reasons behind it, is what we call shoestring engineering, because the engineering time or effort is not put into the design for either lack of funds, knowledge, or whatever other reason. Shoestring engineering, without specifically stating that it is shoestring engineering, is in itself, unethical. If a client paid you to design a system, and later determined that you used shoestring engineering in the process, you would be in breech of contract because you did not provide the full engineering services that they were paying you to perform.

Granted, no one is paying for advice on this forum. Nevertheless, the ethics remain the same, insomuch as you brought up the topic of ethics as an excuse for not providing correct information. So from an ethical standpoint, you either need to provide the correct information, or state why you are not providing the correct information at the time you are providing the aforementioned information. (Note that you specifically stated that you were an authority on the topic.)

Regardless of the level of design, or knowledge behind it, common sense needs to come into play somewhere along the way. And as I’ve already discussed with you in the past, if the 80% derating rule was applicable to the majority of woodworking tools, then the ubiquitous Delta Unisaw could not be sold with a NEMA 6-15 plug attached to it, because it would violate the so called “80% rule” and UL would not permit this tool to be sold with their certification sticker stuck to it.

You keep repeating your advice, but to date, you've never bothered to address the two questions I've posed along the way. Namely, how can a Unisaw carry a UL listing with a NEMA 6-15 plug, and under what possible conditions can a home tablesaw (or similar woodworking tool) ever be considered as a continuous-duty, continuous-load device.

[Mike Cutler]

Rick

While I don't agree with everything in this thread. The terms "continuous duty", "continuous load", "varying load", and "intermittent duty" are somewhat defined in the definitions sections of the NEC. Article 100.

By their definition, and my understanding, and the illustrated addendum and rules changes to the NEC. A tablesaw, dust collector, bandsaw, etc, and including the NEC use of the term "machinery" in the definition, puts the woodworking machinery in a home shop into the category of "varying load" at best, or worse depending on how it is viewed.
IIRC correctly. Continuous Duty is defined as a load running at max for greater than three hours.(2005 book is at work on my desk) The only machine that might come close is a DC. I would still put it under the Varying Load definition.

There are resons that inspectors will require a larger branch wiring size and OCD. I don't agree with the philosophy either.
It is based on protecting the branch circuit conductors from unintentional, or intentional deviations from the branch circuit sizing requirements for multiple loads (motors) that could be placed on the circuit at a later date should the circuit be modified.
I myself think this is folly. Why should I have the burden of responsibility to protect the conductors for any unanticipated modifications in the future not performed by me.
I also have some strong reservations about oversizing the branch, and the OCD when a motor is placed on the circuit. I want that branch sized for that motor. (Multiple motors on a branch of course have a different sizing requirement.)
I also don't like the practice of putting a smaller OCD on a branch with a larger conductor size. It's done, and it's legal, but it can lead someone down the path at a later date. Installing #10awg on a 220/20 amp OCD might lead someone to indiscriminately install a larger breaker at a later date without knowing or investigating the entire circuit.
Size the wiring and the breaker together to comply with the load requirements. If someone needs it bigger in the future. That's their issue.

I agree with you that the 80% rule isn't applicable. I've read that section(s) and paragraph(s) a few times today, and I don't see it as a 100% application.
(As a matter of fact, I've been reading and re-reading the motors, ventilation, and heating and airconditioning sections of the 2005 NEC since this thread started.):eek:


All of my 220 machines came with 6-20's. Interesting that a unisaw has a 6-15???

As much as I like to discuss subjects like this, and I do as long as they remain civil,and people can take things away from it. I would recommend that a person that was seriously interested in obtaining the "most correct" info, without paying for it visit Mike Holt's electrical forum. The forum is populated by liscensed electricians, trainers, inspectors, inspector trainers, and PE's. It's moderated by professional liscensed electricians and inspectors. Be forewarned, they are nice folks, but they have some real strong opinions, and bias, on code compliance issues.

I haven't heard of an "Electrical Technologist". We have "Electronics Technologists" at work. They have a 2/3 year Associates in the related field from the VoTech colleges in the area.

Maybe we need a new forum on "shop electrical". There have to be a few liscenses and inspectors on this board that could moderate it. These are usually the same questions asked even an article might be of benefit.

Right now I'm concerned with "Luminaries",and vent fans in an enclosed shower myself. The GFCI requirements are a bit of confusion( Little bit of passing the buck also). I think I have it worked out though. :rolleyes:,;) .

[Tom Godley]

Mike Cutler - I must say you have expressed my thoughts on this subject much better than I was able to do. Some on the forum are just better at writing in a way that that others can easily understand.

[Ken Fitzgerald]

I'd think it'd be more likely someone would try to put a 30 amp breaker on a #12 gauge and operate it and it would be more dangerous......trying to avert the expense of rewiring with the #10 gauge.

[Mike Cutler]

I'd think it'd be more likely someone would try to put a 30 amp breaker on a #12 gauge and operate it and it would be more dangerous......trying to avert the expense of rewiring with the #10 gauge.

Tom
Thank you for the compliment. I think I am lousy at explaining myself in the typed format.
Rick Christopherson has a very nice web page that has a section on basic electricity, and fundamentals. It's well writtenl and excludes most of the boring in depth explanations of priniples and the associated math formulas.
I highly recommend that anyone interested in learning about electricity in the shop give Rick's site a visit.

Ken
That's an issue also. It is a very obvious visual deviation though in the event of the sale of a house, or a fire.
I wouldn't want to be the one that did it. It would just be inviting an inspector to take a closer look at everything else electrical. Should the situation arise.
Fortunately, there is a lot of "engineering fat", or conservatism built into the code, and the wiring itself. PVC insulated #12 running inside of an NM jacket is alot safer than #12 running inside of a rubberized braid like it used to be.

We spend a considerable amount of time worrying about the wiring and requirements for motors in the shop. They really aren't on long enough to present a major issue, except for maybe the DC, in my opinion.
If there is an area where folks are more likely to be running "closer to the edge", it's lighting. It's really easy to unintentionally overload a lighting circuit.

[Ken Fitzgerald]

Mike,

Just for the record, at the risk of being harangued for "shoestring engineering" I ran the shop lighting in my shop with #12. Two circuits, 2 breakers, 4 rows of T-8's, 3 rows of 3 8' fixtures 4 32 watt bulbs per fixture. 1 row of 2 8' 4 bulb 32 watt bulbs per fixture. Each row has its own switch.

[Rod Peterson]

All of my 220 machines came with 6-20's. Interesting that a unisaw has a 6-15???

Nice post, Mike. By the way, not only does the Uni come with a 6-15 plug, but my DJ-20 (jointer) and DC-380 (planer), both with 3HP motors, each came with a 6-15 plug. My shop is a complete NEMA 6-15 zone! (although I did put 6-20 receptacles in the wall--which accept both).

[mike wacker]

I enjoy the passion that this subject seems to raise. One point that was somewhat covered was the actual name plate amperage data on the "3 hp Motor". As stated in the one post (sorry it was buried in here and I forget who the poster was) a high efficiency 3 hp motor might be 12 amps and a low efficiency 3 hp motor 19 amps. Although that swing seems a little high to me.

The answer to the original question is quite different depending on these amperages. Regardless of derating or any other rule, one should not use the hp rating of the motor to determine cirduit ampacity needs. i.e the question should be, "If I have a motor with x FLAs, what do I size my branch circuit?" rather than "If I have an x HP motor, what do I size my branch circuit?"

Then we can debate derating and future expansion considerations til the cows come home. ;o)

[Rick Christopherson]

Rick Christopherson has a very nice web page that has a section on basic electricity, and fundamentals. It's well writtenl and excludes most of the boring in depth explanations of priniples and the associated math formulas.
I highly recommend that anyone interested in learning about electricity in the shop give Rick's site a visit.Since Mike brought this up, I should probably make sure that everyone knows that my web site is in the process of moving. I am separating myself from AT&T, so I had to go with a new internet host and proper domain name. The new root domain for all of my articles is www.waterfront-woods.com (http://www.waterfront-woods.com), and the link directly to Electricity in the Woodshop is at www.waterfront-woods.com/Articles/Electricity/electricity.htm (http://www.waterfront-woods.com/Articles/Electricity/electricity.htm)

[Rod Peterson]

Just for the record, at the risk of being harangued for "shoestring engineering" I ran the shop lighting in my shop with #12. Two circuits, 2 breakers, 4 rows of T-8's, 3 rows of 3 8' fixtures 4 32 watt bulbs per fixture. 1 row of 2 8' 4 bulb 32 watt bulbs per fixture. Each row has its own switch.

Actually, when I did my shop wiring I used 12ga for the lighting circuit, too. Reason? First, that was the circuit where I knew I would eventually pick off for a ceiling drop or two. I wanted those to be 20A circuits, just like all the ones on the walls. Absolutely necessary? Probably not, but that wasn't the only reason:

Second, and this is the "cost trumps engineering" reason: I bought a 250' roll of 12ga wire for the shop. Would it make any sense to go buy a 50' roll of 14ga just to do the lighting when I had plenty of the 12 ga left over after doing the walls to do the lights? Of course not. And 15A breakers vs 20A breakers are virtually a wash at the cash register.

For those concerned about losing shop lighting if I trip the breaker using a tool from one of those overhead drops, I have a separate, 15A, minimum lighting, circuit that is turned on when I first enter the shop. They're actually the original garage lights left over when I converted it to a shop (in case some misguided soul wants to convert it back after I tip over).

[Sandra Force]

If you are wanting to do this right I would go with 10 ga wire and 30 amp breaker or double 20 amps. When we wire we almost never put 12 ga or 20 amp breakers on 220v. My standard electrical for outlets and lights for the business is 14ga with 15 amp for light duty, anything that is going to be loaded down gets 12ga and 20 amp. Getting shut down due to overload in the middle of a project is not worth the savings. If you have to rewire due to not enough amps in the future because of adding equipment it is going to cost you a lot more money than doing it now.:eek: The pain of it $$$$.

[Mike Williams]

Thanks to all for the spirited discussion and opinions. I thought I would close this out by letting you know what I'm going to do in my new shop.

I talked today with the electrical sub-contractor (owner with over 30 years experience). We are going to install 10 gauge wire, NEMA 6-20 receptacles and 20 amp breakers.

The rationale is that the 20 amp breakers should be adequate and appropriate for the 3 HP motors. However, if there is an individual case where it isn't, or if I change to a larger machine in the future, I can change to a 30 amp breaker and a NEMA 6-30 receptacle with little effort.

Thanks again.

Mike

[Mike Cutler]

Mike

Congrat's on the new shop. Be sure and post some pic's when it's all up and running.

Don't daisy chain off of that new branch, or we get to have this discussion again.;) ,:D ,:D.

[Daryl Upole]

Hi,

When I built my shop, I ran 1" PVC conduit under the slab to strategic points for power. This lets me decide what wires, circuits, etc. to run at any time. It makes it easy to change later. So, conduit is not required for code, more costly and time-consuming to install. But, I do it all myself so the extra effort sure makes it easy down the road. I've never regretted installing conduit in any of my projects.

Another suggestion I have is to pull some wiring that is not used now before covering up walls. I agree with the gentleman who said the cost of the heavier gage is negligible. So, I've run 10/3 w/ ground from near the breaker box to attics, etc. So, if I ever want I could easily grab another circuit up to 30 amps.

[Rick Levine]

It really depends on the motor. My Woodtek DC that draws 19 amps needs a 30 amp circuit breaker to start. The electrician mistakenly installed a 20 amp breaker and 12 gauge wire and every time I started the unit it blew the beaker. I had to hire a different electrician to run a new line with 10 gauge and a 30 amp breaker to solve the problem. It was a costly mistake.

[Shawn Walker]

It doesn't seem to matter what WWing forum your on... People sure get AMPED UP over these electrical threads. :p

Cheers Shawn.

[Art Mann]

Having recently done some rewiring of a shop for a good friend, I will offer one comment that is highly relevant if you are doing your own work. 10 gauge is much more difficult to work with than 12 gauge. I will only put in 10 gauge in my shop if there is truly a reason to do so. If you are paying someone else to do it, it really doesn't matter.

[Bernie May]

I am running both 10 and 12 g in my shop as we speak. It's not that much harder to run the 10. I can't believe people keep saying it is hard to run. The difference is negligible. I guess if you make your hole too small going through the studs it could be harder.

[Tom Veatch]

I am running both 10 and 12 g in my shop as we speak. It's not that much harder to run the 10. I can't believe people keep saying it is hard to run. The difference is negligible. I guess if you make your hole too small going through the studs it could be harder.

I assume you're talking about pulling the wire runs. I agree there's not that much difference even though the 10ga is noticeably stiffer. However, when it comes to working inside the boxes, I find that the difference between 10ga and 12ga is most definitely not "negligible". But, that's just me. YMMV.

[Art Mann]

Running wire through the wall is trivial. Where it gets difficult is when you wire in the outlets and try to stuff the wire back in the box. I realy don't care whether you think it is easy or not. I'm pretty sure people will agree with me if they do a lot of it.

[Steven Wilson]

Air Compressor and Dust Collector - 30A because they're continious duty (hence the 125%), 20A for the other stuff (table saw) because they're intermitant duty (no need for the 125%). Of course this assumes that none of the FLA ratings of the 3hp motors are 20amp or larger.

[Jim Becker]

Running wire through the wall is trivial. Where it gets difficult is when you wire in the outlets and try to stuff the wire back in the box. I realy don't care whether you think it is easy or not. I'm pretty sure people will agree with me if they do a lot of it.

I do agree, but one of the solutions is to use a deep, double box with a single outlet mud-ring. Lot's of space to manipulate the stiff wire... ;)

[Rob Will]

If you can afford it, wire it any darn way you want to. :cool:

Just as soon as you say "never" anything bigger than 3hp, there will be some "deal" come along on some kind of old iron that you can't live without.:o

Personally, I would use 10 ga wire and 30A breakers and be done with it.

Rob

[Daryl Upole]

I agree with Jim on the boxes. That's what I do - use lots of boxes and I'm not stuffing things in too badly. NEC has guidelines on that - but you'll find it a lot easier if you go more conservatively than that. It is definitely harder working with the #10 than #12 in tight quarters - but one circuit in a 4 x 4 box should not be too bad - especially if you add the depth as suggested by Jim.

[glenn bradley]

20a with #12 is probably the response you will get most. My approach was to run #10. I have 2HP machines and run 20a breakers but a 3HP is on my list. My thinking was that if I need to upgrade, all I have to do is change breakers and outlets. If I would have wired with #12 I would be re-wiring (possibly). I only wanted to do it once.

[Art Mann]

Glenn,

If you buy a 3 hp machine, you will probably not have to upgrade to a 30A circuit unless the motor is of exceptionally poor quality. I suspect a majority of people who have been forced to replace thier 20A breakers with 30A had a defective breaker. They do go bad.

Art

[Tom Veatch]

If you buy a 3 hp machine, you will probably not have to upgrade to a 30A circuit ...


Totally agree. A 3HP motor should have an FLA somewhere around 15A at 220-240V. A 20A circuit is quite sufficient. Going to 5HP gets into the 20-25A FLA range and the need for a 30A circuit.

[scottj owen]

I live in Alberta Canada, and here your full load amps can only be 80% of your breaker size, so any machine with a FLA of 17 or more has to be on a 30 amp breaker. I am sure that is overkill in most cases but if you have a fire the insurance company will build you a new shop.
I would just check your codes in your area.
Have a great one!

[Louis Rucci]

All good information here, as I'm in the process of wiring my shop. ON my heavy power tools, like yours, I've decided to give them 10 gage wiring. Just because the wire can handle a higher current, you still need to use the appropriate breaker for each tool. I just want the extra current handling capacity for both safety and possible future power needs.

Anyway, that how I based my wiring decision.
Louis

[Art Mann]

I live in Alberta Canada, and here your full load amps can only be 80% of your breaker size, so any machine with a FLA of 17 or more has to be on a 30 amp breaker. I am sure that is overkill in most cases but if you have a fire the insurance company will build you a new shop.
I would just check your codes in your area.
Have a great one!

Interesting. There are people on this board who have claimed that running a 17A motor on a 30A breaker is dangerous. Apparently, the Government of Alberta doesn't seem to think so!