Machine Amperage Question

[Corey Pionk]

Ok with the new machines coming in very soon I'm putting in a new subpanel and need to know what Amp breakers to get for the following:

1. 5hp General Cabinet Saw
2. Yorkcraft 5 hp 20" planer
3. Oliver 3hp 10" Jointer

So does anyone have any of these machines to tell me what breaker size to use.

Thanks

Corey

[Don Baer]

as a rule of thumb for 220 1PH you can count on 5 amps/hp.

So 5HP=25 amp
3Hp=15 amps

This is a rule of thumb and depends on the motor manufacturers effencies.

[Ted Jay]

Ok with the new machines coming in very soon I'm putting in a new subpanel and need to know what Amp breakers to get for the following:

1. 5hp General Cabinet Saw
2. Yorkcraft 5 hp 20" planer
3. Oliver 3hp 10" Jointer

So does anyone have any of these machines to tell me what breaker size to use.

Thanks

Corey

Can you download any of the spec sheets from the place you bought them?

[Steve Cox]

All of the tools should have their electrical requirements posted on them. You then want to go at leasT 25% over for the circuit. 50% is better.

[Jerry White]

Corey,

I don't have any of those machines, but mathmatically the current draw should be approximately 16 amps for the 5 hp machines and 10 amps for the 3 hp machine. The manufacturers nameplate ratings may vary somewhat from this.

You should be OK with a 30 amp breaker and 10 guage wire for the 5 hp applications and with a 20 amp breaker and 12 guage wire for the 3 hp application.

[Rick Christopherson]

You don't need the spec sheets. A 5 hp motor will need a 30 amp circuit with #10 wire. The 3 hp motors will need a 20 amp circuit with #12 wire.

Oops. Didn't see Jerry's post at the same time as mine. Although the circuit information is correct, his amperage values are too low.

[Stephen Dixon]

5HP = 28 amps full load current, x 125% for wiring and devices, and 250% for the circuit breaker.

3 HP = 17 amps, X 125% = 21.25 wire or 12 gauge, with a 45 amp breaker

5 HP motors that's 8 ga. wire with 40 Amp plugs and receptacles, with a 70 amp breaker.

BTW by code, you must use the NECs numbers above, not the FLA listed on the motors.

I know, some of you out there will wince at recommending 8ga wire on a 70 amp breaker, but that is what the code allows. Specifically it is the job of the thermal overloads to provide overcurrent protection, the branch circuit breaker is for ground faults and short circuit protection.

Particularly when you get to 5 HP motors you have to look at the whole circuit for the wiring.

The above is what the code allows, what I would do, is use a 10ga. 30 amp circuit, with a 30 amp circuit breaker for the 3 HP motor, and 8ga. 40 amp circuits, with 40 amp breakers for the 5 HP motors, but I would not be afraid to install a 50amp breaker for the 5 HP motors if I had trouble starting one or both of the motors.

Steve

[Randy Meijer]

.....5 HP motors that's 8 ga. wire with 40 Amp plugs and receptacles, with a 70 amp breaker......
what I would do, is use .....40 amp circuits, with 40 amp breakers for the 5 HP motors.....

This whole message puzzles me; but I am particularly confused by your recommendation which seems to conflict with what you say the NEC calls for??

[Stephen Dixon]

I know I'm not the best at explaining this, but the hard part is to get past the breaker being larger than the wire size would indicate. The breaker in a motor circuit is to protect against ground faults and short circuits, the wire is protected by the motor or starter thermal elements.

[Gary Sostrin]

Current requirements for machines can have 2 different values. One for steady state and one for initial turnon (Inrush). The initial turnon can be 25% higher than steady state for a few millisconds. These few milliseconds could trip the breaker or stress it to fail later on. So plan appropriately. Also consider the distance that the power has to travel from the fuse box. When in doubt size for the inrush, and that should take care of any voltage drop due to long cable runs.

[Larry Cooke]

...I'm putting in a new subpanel and need to know what Amp breakers to get for the following:

1. 5hp General Cabinet Saw
2. Yorkcraft 5 hp 20" planer
3. Oliver 3hp 10" Jointer
How far is the sub panel from the motors? Are you creating a separate circuit for each one?

5hp motors generally have a constant load of around 20-25 amps, but the startup load is higher - need to check the motors specification plate to be sure. 3hp motors are usually 15-20 amps load while running and again the startup load is more.

Realistically, you should be safe with a 30 amp breaker for the 5hp motors and a 20 amp for the 3hp motor but...

I'd seek advice from a licensed electrician to be sure everything is kosher. Is the sub panel sized properly, proper wire size for the wiring between the main panel and sub panel, and proper wire size from the sub panel to the motors?

There's a lot of variables you're not providing information for with your post. I'd hate for you to take anyones suggestions (my self included) for gosphel since there are some critical details missing.

Larry

[lou sansone]

I know I'm not the best at explaining this, but the hard part is to get past the breaker being larger than the wire size would indicate. The breaker in a motor circuit is to protect against ground faults and short circuits, the wire is protected by the motor or starter thermal elements.

hi steve
can you please provide chapter and verse in the NEC for your recommendation ?

thanks
lou

[Steven Wilson]

Stephen, What I remember a few years back from my inspector was that I could go with breaker recommendations like yours if I was really wiring a motor circuit. That is, I was hardwiring to the saw (with appropriate disconnect) and it was only used for motors. He chose to treat my circuits as 220V branch circuits (i.e. I use twist lock plugs and can plug what ever I want into them, including motors) and so my 3HP motors would work nicely on a 20A/12ga circuit and my 4.8HP motors would play nicely on a 30A/10ga circuit. He suggested making a motor circuit if I experience problems starting the motors on a branch circuit. I haven't ever had a breaker problem on startup so the branch circuit is fine. The wire sizing is the same for both just the breaker values vary so wouldn't the branch circuit be more conservative?

[Barry O'Mahony]

hi steve
can you please provide chapter and verse in the NEC for your recommendation ?

thanks
lou

This is all from Article 430 of the NEC. I think some explanation is in order:

Article 430 specifices requirements for motors and motor circuits.

circuit conductor ampacity - The Article says to ignore the nameplate FLA on the motor, and instead go by the HP rating. Take that horsepower number and look up the ampacity on the table in the Article, which will most certainly be higher than the nameplate FLA. The intent here is to cover the circumstance where, sometime in the future, the motor is replaced with a new one of the same HP, but perhaps a higher FLA. Thus, the conductors are sized for a "worst case" situation with the new motor.

short circuit and GF protection - The article says this may be provided by a breaker that is rated a maximum of 250% of the current found in the aforementioned Table. It doesn't have to be this big, but if you need to increase the rating in order to prevent it from tripping at motor startup, this is the biggest you can make it.

But what about overcurrent protection for the circuit conductors? A 70A breaker can't protect 8 AWG conductors from an overcurrent situation.

Overcurrent requirements are defined in 240-4. In most cases, it refers the reader to the tables in Chapter 3 most people are familar with. But for motor circuits, it refers the reader to Article 430 instead. And in '430, it says that the motor overcurrent protection may serve as the circuit conductor overcurrent protection.

One thing I've always been concerned about, though, is that in 240-21 itsays that the overcurrent protection for a conductor must be on the line side of the conductor, except in certain circumstances. And a single motor on a branch circuit isn't one of the listed circumstances. But if one reads the NEC Handbook (a publication of the NFPA that explains the NEC section-by-section), it specifically says it is OK, so I guess it is. I'd still like it if Article 430 explicitly said the overcurrent protection could be on the load side, though.

I agree with Steve Wilson's inspector that this method really shouldn't be relied on in plug-and-cord connected motors, however. There's no guarantee that a motor with an integral OCPD will always be plugged into the receptacle, so there's no way to ensure that the conductors will have overcurrent protection even using this method.

Which brings up the "interesting" question of the plug and receptacle. According to '430, these together constitute a motor Disconnecting Means. As such, they must meet the horsepower rating of the motor. The intent here is to ensure that in an emergency, you can cut all power to the motor by pulling the plug, without arcing or the plug contacts welding themselves to the receptacle. But the fact of the matter is that the horsepower ratings for NEMA connectors are surprisingly low. As an example, single-phase connectors with a 5 HP rating don't exist; even the biggest one, a NEMA 14-60, is only rated at 3 HP.

So supposedly, it would be a Code violation to put a 5 HP device on a plug, or to use anything smaller than a 50A plug on a 3 HP machine. But we know this is not common practice. Either the Disconnecting Means provision is the most-ignored provision in the NEC, as some electricians just shrug it off as, or cord-and-plug connected woodworking tools aren't considered "motors" under the NEC at all. Some electricians and inspectors regard them a "motor driven appliances". In these case, most of '430 doesn't apply, including the requirement that plugs and receptacles be horsepower rated. And in this case, the branch circuit breaker must be sized to protect the circuit conductors.

'sorry if this is more than what some wanted to know about this. :o

[Steven Wilson]

Thanks for the explanation Barry. You can never have too much information and what you passed along is relevant for most of us. I just figure that if I'm friendly and honest with the Electrical Inspector and do some research before asking him questions that I'll get a fairly good response; so far, so good. NEC discussions are always good.

[Stephen Dixon]

You did a much better job of explaining this than I ever could.

Steve

[Allen Bookout]

I have been reading this thread with interest as I recently installed an Ingersoll Rand air compressor with an Emerson continous duty motor that is 5hp (22.5 fla listed) and I am not sure that it meets code from what I am seeing. IR recommended a 60 amp breaker, to handle the starting load, with #10 wire on its own circuit (no plug). 10 feet of wire from CB box to motor. From what I see here it seems as though #8 wire might be required or is that one wire size larger than code to remain conservative? Is #10 suitable since it is on its own circuit and such a short run? Is the 60 amp breaker out of line? It works fine so far but I would like to be covered legally.
Allen

[Luther Oswalt]

My 220V circuits are wired the same as Steve Wilson described his were. Not a problem ever nor any indications of one. I would think that a very high percentage of shops are. This is the first time I have seen reccomendation for a non-commercial shop wiring be wired with this heavy a amp circuit breaker. Are you folks sure that those ciruit breaker ared sized correct for a non-commercial application where twist type plugs are to be used?
Leo

[Rick Christopherson]

Cut the Crap!
When I first saw these replies I thought they were jokes, but it appears they are dead serious. What I've read in the last couple of pages (no names) is the most infuriating misinterpretation of information I have seen in a long time. This is a case of taking information from one area and applying it to another area, and it does not fit here!

The NEC goes into a lot more information about motors than the limited explanations above, and for something like a tablesaw, none of this massive overkill is required.

When you misquote the NEC like this, the urban myths will last for months on the internet, and that is why I am coming down so hard on this.

As was already stated, the 3 hp tools need 20 amp circuits and the 5 hp tools need 30 amp circuits.

[Allen Bookout]

So Rick, What you are saying is that a 5hp motor, even if it starts under load such as an air compressor, should be fine with a 30 amp breaker? I was told that a 30 amp breaker would trip every time that it started. I could go buy more breakers of various sizes and keep going up if it didn't work but if the 60 amp breaker that Ingersoll Rand recommended is safe I will just leave it alone. #10 wire and 60amp breaker, 5hp running and less than 10 feet of wire. Allen

[Rick Christopherson]

So Rick, What you are saying is that a 5hp motor, even if it starts under load such as an air compressor, should be fine with a 30 amp breaker?
My Curtis Toledo has been running on a 30 amp breaker for over 10 years without ever tripping, and I have even had it on a pretty short duty cycle with 3 DA sanders running simultaneously. It is the short duty cycles with repetative restarts under load that can pre-heat a circuit breaker (and the wiring) to the point that they will trip prematurely.

I don't know who at IR recommended a 60 amp breaker for this application, but they need a swift slap.

[Frank Chaffee]

I always thought that circuit breakers sized for running amperage would accommodate inrush current upon starting a motor. Higher amperage requirements than are usually experienced in a small shop need fancy stuff like “heaters” that we’d best have spec’d by an electrician.
True or not true?
Frank

[Allen Bookout]

I wish that I had not involved the Ingersoll Rand tech people as they were a big help to me in other areas and trying to help me on this issue. So please, just forget that I said that they recommended anything as I do not want to cause problems for anyone at that company.

Thank you for your response!!! Allen

[lou sansone]

Although I would not express the same sentiment as Rick has, something does not sound right with suggesting that that NEC would allow 8 guage conductors to be on the load side of a 70 amp breaker. I have worked for years as an electrician before becomming a Electrical Engineer and I have not come across this before.

lou

[Rob Russell]

Per the calculations in article 430, it could be absolutely appropriate to have a 70 amp inverse time circuit breaker protecting #8 THHN.

Use an example of a 5HP, 230v, single phase motor with a nameplate current rating of 24 amps and service factor of 1.25.

From 420.22(A), the conductors will be at least 125% of the FLA rating from the tables, 28 amps * 1.25=35 amps. #8 THHN is rated for 40 amps, using the 60 degree terminal column.

From 430.52(C)(1), the branch circuit short-circuit and ground-fault protection can be up to 250% of the FLA rating, 28 amps *250% = 70 amps.

So - indeed - we can have a 70 amp breaker providing short-circuit and ground-fault protection for said motor circuit.

We're not done yet.

We also need an overload. That would be sized per 430.32 at 125% of the nameplate current rating or 1.25 * 24 amps = 32 amp overload.

It's important to note that the above calculations are for continuous duty motors. It's also important to note that the above calculations are - most likely - not how I would wire the circuit for a 5 HP, 230V compressor in my shop.

I'd wire a circuit with #8 to help reduce voltage drop at startup and protect it with a 30 amp breaker. In this scenario the circuit breaker is serving 3 purposes - short-circuit protection, ground-fault protection and motor overload protection. If that tripped, I'd go to a 40 amp breaker but would also add a separate motor overload because I could now have a situation where the motor was continuously drawing 167% percent of it's nameplate rating and that's a potentially hazardous situation.

The NEC rules for motors are different than the rules for normal branch circuits. The rules for normal branch circuits are more conservative in terms of breaker sizing in relation to conductor gauge. That's because the circuit breaker serves more purposes in a normal branch circuit than in a dedicated motor circuit where the motors have separate overload protection. It's not just about protecting the circuit conductors, it's also about protecting the motor.

The simplest thing to do is stick with normal branch circuit sizing. If the 30 amp breaker works for your compressor, there's no reason to go larger. If you need to go to a larger breaker, you need to understand the rules that go along with increasing breaker size and motor overload protection is part of that.

Rob
Addy protocol: not a licensed electrician

[Barry O'Mahony]

Cut the Crap!


Well this should be interesting...

It would help if you were more specfic as to what exactly is "crap", what is "infuriating misinterpretation", and what is a "misquote".


As was already stated, the 3 hp tools need 20 amp circuits and the 5 hp tools need 30 amp circuits.

For a plug-and-cord connected tool, yes my post agreed with that. For a direct-wired circuit, the local AHJ may not agree that this is always the case.

I am reluctant to accept your opinions without justification; partly because I took a quick glance at your "Electricity in the Woodshop" page and spotted a few errors. For example, in your section 1.6.3:

A circuit breaker is not intended to protect the appliance, only the wire between the breaker and the outlet.There are numerous paragraphs in the NEC which contradict this statement; e.g.,, 240-5(B) & 422.11 are two.


National Electric Code mandates that ALL Hot wires going to a load must, not only have a circuit breaker, but ALL circuit breakers feeding that device must trip together. No it doesn't. Common trip is only required when multiwire branch circuits feed both line-to-line and line-to-neutral loads (210-4(C) Exception No. 2). Otherwise it is not a requirement.

[Barry O'Mahony]

Although I would not express the same sentiment as Rick has, something does not sound right with suggesting that that NEC would allow 8 guage conductors to be on the load side of a 70 amp breaker. I have worked for years as an electrician before becomming a Electrical Engineer and I have not come across this before.

lou

Lou,

Take a look at this thread on Mike Holt's NEC forum for additional example:

http://www.mikeholt.com/codeForum/viewtopic.php?t=24713

The modoerators on that forum are on the committee that write the NEC, so I'm inclined to take their word for it. ;)

Also, if you can look at a copy of the NEC Handbook, look at the explanatory text for 430-52. it has a few paragraphs just on this topic. I only have a hardcopy of the Handbook, so I can't easily paste the section here.

[lou sansone]

Lou,

Take a look at this thread on Mike Holt's NEC forum for additional example:

http://www.mikeholt.com/codeForum/viewtopic.php?t=24713

The moderators on that forum are on the committee that write the NEC, so I'm inclined to take their word for it. ;)

Also, if you can look at a copy of the NEC Handbook, look at the explanatory text for 430-52. it has a few paragraphs just on this topic. I only have a hardcopy of the Handbook, so I can't easily paste the section here.

Thanks for the link... There does seem to be a dispute about this same topic over there as well. The way I read the post that you linked to was that for short distances a motors OCPD located very close to the motor could be higher than the wiring code would allow, but the OCPD for the entire circuit was governed by the wiring tables and would represent a more traditional view that the OCPD should never allow for excessive loads to be sustained and thus risk fire. This was the moderators position as best as I can read it. But just for completeness, and now that you have gotten my attention I will make it a point to fully understand / and or correct / this issue.

regards
lou

[Rick Christopherson]

Barry, the issue I have with this is that these postings wrongly lead the casual reader to believe that they need huge circuits for the tools listed. Neither you nor the other poster answered the original person's question; you simply quoted code for nonapplicable situations. You both misapplied what the code will permit you to do, and presented it as though it is what the code requires you to do. Regardless whether you can backpeddle fast enough to claim you were only stated what was permissible, this is not how the information was presented.

In several places you used the word "requirements", which implies to the reader that it is information that they are mandated to follow. And the implication that "it would be a code violation" to put a 3 hp (e.g. Unisaw) motor on anything less than a 50 amp plug is the most nearsighted thing I have read in years. It doesn't matter that you prefaced this with "supposedly", you deliberately and knowingly left the impression it is a requirement.

You also didn't take into account the duty cycle of the machines listed. All of these machines have a very low duty cycle, and none of them are automatically controlled. Nowhere in your dissertation did you address the code variations with duty cycle for motors.

Your discussion on cord and plug connections leaves me stymied as to how you could even come up with this. Does this mean I need to go down to the shop and cut all the power cords off my routers? By the way, if you think a NEMA 14-60 is the biggest connector available, you definately need to get out in the real world a little more.

I don't pretent to be an expert on code and I know my limitations. However, you think you know the code more than you actually do, and that is far more dangerous.

As for my article, if those are the only pedantic errors you can come up with, it falls a little short of knocking holes in my credibility. That article has been on the Internet for over 10 years and read by hundreds of thousands of people, including quite a few electricians, inspectors, and engineers (I know because they email me). Do you honestly think that after 10 years you will be the first person to find a significant mistake in it? Surprisingly, when I type your name and electricity into Google, I get no applicable hits.

[Allen Bookout]

I am not really a part of this discussion, thank goodness, however I did get concerned about using a 60 amp breaker and #10 wire for my 5 running hp, 22.5 FLA, aircompressor motor so for anyone that is interested here is what I did. I replaced the 60 amp breaker with a 30 amp breaker (due to some information here) and ran the unit through five cycles of one minute running and 15 seconds off and it did not trip the breaker one time. I realize that the test may not be valid for a real world situation but it appears as though I may not have any trouble with it and I feel a lot better. Allen

[Rick Christopherson]

Actually Allen, you really are part of the discussion, but not in a bad way. You are one of the innocent victims seeking information, but getting misinformation in return, and that is why my ire was raised with these other postings. I was worried that you thought I was referring to you in my previous posting, so I am glad to know that you don’t think this.
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Actually, the reason why I wanted to respond to your message is to confirm your findings as being valid. Even though a duty cycle of 1-minute on and 15-seconds off is not real-world for a compressor, it is bordering on a worse-case situation for loading a circuit. For that reason, you can be assured that your 30-amp breaker and wiring will suffice during real-world usage.
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Your message is a positive contribution to this discussion.

[Allen Bookout]

For that reason, you can be assured that your 30-amp breaker and wiring will suffice during real-world usage.
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Thanks Rick! I am now comfortable with my situation.

I will continue to watch this thread for my own education but will keep my head low.

Thanks to all for bringing this subject to the forefront.

Allen