Need 3 phase Assistance

[Matt Hutchinson]

As I am doing research into wiring 3 phase circuits, I keep coming up short. I mean, things are still a little hazy, and I would love help nailing down the details.

1.) Assuming I am using 10 gauge wire, do I need 3 conductors and a ground, or do I also need a neutral? For some reason I seem to be getting mixed messages in this department. (Or I am just misunderstanding.)

2.) What's the least expensive way to get power to the four 3 phase tools. Meaning, how do I connect four loads to the one power source with the least expense? Do I need a 3 phase load center, or do i just run all the tools into one junction box and feed it directly from the converter?

3.) Do you have any pictures of your 3 phase wiring/circuits?

Thanks for any help you can give!

Hutch

[Travis Porter]

I am not an electrician, so you get what you pay for.

1. 3 conductors and a ground. That is the way all my 3 phase tools are laid out.

2. I daisy chained the outlets just like you would do for single phase outlets. I want a 3 phase load center, just haven't found one cheap enough for my budget.

3. Sorry, no pics. I come out of a phase converter and go to twist lock 3 phase receptacles. The receptacles and plugs gave me sticker shock!

[Matt Hutchinson]

Yeah, same here. I went to price out the plugs and just about had a fit. Did you use twist lock plugs? I was told there wasn't any other kind available for this type of setup, and that means about $60 per tool just for the stinkin' twist locks!! Did you find any bargains?

Ok, so what you are saying makes a lot of sense. I think I am in a similar situation, not being able to find an affordable load center and all. So I think I will proceed to plan the receptacles in series, like you said.

Cool Stuff! Thank you!

Hutch

BTW, did you run the circuit yourself?

[Rob Russell]

When I was looking for 3-phase stuff, I found Ebay to be a good place. Just be patient and you can pick up great deals on plugs/receptacles. You can also find a good load center cheap.

For my equipment (Felder), I needed 3 hots + ground, but also a neutral because there are some 120v control circuits in the machinery control panels. That's not going to be normal.

It's wise to put a load center between your machinery and the phase convertor. That way you can size the circuits to the machines.

[Rick Christopherson]

First, the easy answer. Not only do you not need the neutral, but because this is coming from a phase converter, you CANNOT use the neutral under any circumstances. Regardless how the motor is wound internally (delta versus wye) you NEVER connect the neutral to a motor!!!!! (And that holds true regardless whether it is true 3-phase or generated 3-phase, but it becomes absolute when dealing with generated 3-phase.)

Secondly, 3-phase power uses a lot less amperage per horsepower than single phase, so it is not very likely that you need #10 wire. #10 wire is for 30 amps, and at 3-phase, 30 amps gives you 11 to 12 horsepower!!! Anything less than 5.5 horsepower at 3-phase can be run with #14 wire, and #12 wire will give you up to 7.5 horsepower.

If you are powering several tools from the same converter, then it is probably in your best interest to use a small 3-phase load center. I think you could do this with raw terminal blocks, but it is not the best solution. Oh, as I see Travis pointed out, daisy chaining outlets is fine too.

I prefer the load center because you would bring in the two house phases separately, and only the generated leg comes from the converter. There are a lot of ways of doing this, but this is the most straightforward.

[Rick Christopherson]

For my equipment (Felder), I needed 3 hots + ground, but also a neutral because there are some 120v control circuits in the machinery control panels. That's not going to be normal.This is a special case because those control circuits are single-phase, not 3-phase. It should be pointed out that when you do this, you are actually taking the original single-phase house power to accomplish this task, and it is independent from the phase converter (even if you think it is going through the converter, it is not).

[Matt Hutchinson]

Aaaahhhh, I love the information age.....

So the largest tool I have is an old 5 hp, but it's 440V at this point. I am going to take it to a motor shop to re-lead it (for 230V), and if that doesn't work, I will have to have it rewound. So, without running out to the shop to check its amperage, I may need 10 gauge for that one tool....maybe. But great to know that I may only need 12. Any way to shave off a few dollars here and there is helpful.

And the clarification of the neutral helps a lot too.

The more info the better. Thanks so much!

Hutch

[Bruce Page]

Matt, do you have 3 phase coming into the box? If not, are you planning on using a converter e.g. static, rotary, vfd?

[Rick Christopherson]

So the largest tool I have is an old 5 hp, but it's 440V at this point. I am going to take it to a motor shop to re-lead it (for 230V), and if that doesn't work, I will have to have it rewound. So, without running out to the shop to check its amperage, I may need 10 gauge for that one tool....maybe. At 440 volts, a 5 hp motor only draws 7 amps. It is a common misconception that the higher the voltage, the larger the wire needs to be. This is not correct. The size of the wire is only dependent on the amperage. If this is your biggest motor, then all of your wiring can be 14 gauge.

However, don't confuse this with the requirements on the line-side of the phase converter. Your phase converter supply wire needs to be larger than the output wire.

[Matt Hutchinson]

Actually, I am still planning on using 10 gauge wire into the converter. But what I meant about the 5 hp motor was that switching to 230V would double the amps, but if it's 7 amps to begin with, then it's irrelevant anyway. :rolleyes:

Bruce, I am going to be using a 10 hp rotary converter. (I chose to go much larger than I need right now cuz it wasn't much more expensive, and I may want to run multiple tools at once down the road.)

Hutch

[Thomas Syrotchen]

Matt,
I'm not sure if I understand your response below about the 7 Amp or not. If you use a higher voltage on a motor then the current will be reduced. Most industrial stuff is run on 460V because it requires less current and hence a smaller conductor. There are other reasons before I'm quickly corrected, but it certainly one advantage of using the higher voltage. If you rewire a motor for 230V you will double the current draw for the motor and hence require a larger conductor. The nameplate on the motor should show two numbers for Full load Amperage (FLA) one for 460 and one for 230 if its a dual voltage motor. When sizing a conductor, you should read the FLA from the Nameplate, motors will vary on current draw based on a few factors not all 5HP motors will draw the same current and I come up with 8 amps at a minimum for a 5HP motor at 460V with no losses. 10 amp I believe would be a more realistic ball park figure when you account for the efficiency and power factor. If you wire it for 230V your looking at 20 amp ball park figure. Conductors should also be sized at 125% of FLA at minimum. I personally use 150%, it rarely is much of an increase in cost.

Depending on what your trying to accomplish with a "load center" there may be more economical ways of accomplishing the task. If your are simply looking to protect branch circuits, fuse blocks are normally the most economical way to go. If you looking remove power from a device and provide circuit protection, then fused disconnects or a fuse block and a local disconnect may again prove to be more economical. If your looking to distribute power in one box and provide circuit protection, then I'd look for a prebuilt box on E-bay.
My two cents on sticker shock, remember that your buying items that are built for industrial type uses that are usually built for a more demanding environment. I hate the prices too, but I haven't had to replace anything I've bought for home as well.

A few things you may want to keep in mind as far as running multiple tools at once.
Check with the manufacturer, but some size their converters using 746W/HP of power output based on the idler motor size with no loss. Since motors in the real world have loss, they use more power than 746W/HP. A 10 HP rotary converter may not handle two 5HP motors running. Now factor in that at start up a motor can draw up to 150% of it FLA and one can quickly overload a phase converter. It all depends on how the manufacturer list their size. Since marketing has a say, my bet is that 10HP converter may not have a lot of capacity left on it once you factor in starting that 5HP motor.

[Rollie Meyers]

Motors are quite different then normal branch circuits which means the ampacity can be used as listed in table 310.16 if conditions are met per art. 430 of the NEC. BTW, this means 14 AWG is rated for 20 amps, 12 AWG is 25 A., read it carefully to apply the rules.

Article 430---Motors,Motor Circuits,and Controllers.

[Matt Hutchinson]

LOL! Tom, I guess I didn't really explain what I was saying clearly. I actually was trying to say what you just said. That is, if I were to take a 460V motor and convert it to 230V I would double the draw. That's why I said I didn't know if I would still need 10 gauge for that one tool, but I see now that 10 still seems a bit oversized.

As for the converter, I don't know all the details. It was built by a guy in New York under the business name WNY Supply. A number of fellas on a machinist forum said it was a good converter for the money, so I thought I'd give it a try. Running multiple tools on it is probably okay, because I only have one 5 hp machine, and the rest are 3 hp or less. But running multiple tools is not something that would happen often. Only if I had someone helping me with a project.

In an ideal world, I would have the machines breaker protected on their own circuit. But putting them on one circuit will get me started I think. Could you elaborate about the fuse blocks? Do you have a link to a pic?

Thanks everyone!

Hutch

[Thomas Syrotchen]

Matt,
If you go to WNY's website, they have a sizing chart. If I read it correctly, based on their sizing chart you would be limited to 7.5HP of total load on a 10HP converter to allow the starting of your 5HP load. In other words your 3HP load running and then trying to start your 5HP load may exceed the capacity of the converter. Likely your 5HP load will start, but at the same time your causing damage to the windings on the idler motor and ultimately shortening its life. Based on your 5HP 3HP I'd probably look at a 15HP unit. WNY though should be able to help you determine if you really need a 15HP unit. Obviously the other option is to run one machine at a time, or never start the 5HP unit with another machine running.

A fuse block image.
http://images.grainger.com/B282_27/images/products/small/SMALL-4XF45.JPG

You could probably do fuse blocks for under $30 a machine, and maybe half that on ebay.

As Rollie pointed out, motor circuits have their own section of the NEC and for good reason as they place a much more complex load on a circuit than your average 60W light bulb. Correctly sizing conductor isn't as simple as saying I need 10 AWG or 12 AWG. I'd echo Rollie's comment, spend some time reading the NEC.

[Matt Hutchinson]

Okay, thanks for the heads-up (and all the other info)! :)

Sorry, please bear with me.

So, the fuse blocks protect the motors. If I chose to ran 10 gauge with a 30 amp breaker, the circuit would be way more than I need for most of the machines, but the fuse blocks at the individual machines would protect the motors while the 30A breaker protects the wire? (Just trying to make sure I comprehend the concepts.)

Hutch

[Scott T Smith]

Matt, are there any plant closings near you? I recently saved thousands of dollars on some industrial 3-phase panels by purchasing them from a closed textile plant and removing them myself. Plus, I was able to get the breakers that I wanted.

In my previous shop, I came out of the phase converter and fed an inexpensive 3-phase load center, and then hard-wired the equipment to that load center, using the appropriate breakers for each piece of equipment.

[Thomas Syrotchen]

Matt,
No problem it can be confusing. You would come off the phase converter and hit a fuse block for each machine. On the other side of the fuse block you would wire each individual machine. Wire size should exceed the current requirement for any motor. Therefore the fuses should be sized for the motor on the circuit which would in turn protect both the conductor and the motor. Its the advantage of using fuses for each branch circuit, you can protect both the motor and the conductor. If you feed all machines off of a single fuse block, your likely only protecting the output side of the phase convertor at best which may already be protected by the manufacturer.
Think of it as a water header feeding different areas of the house each with its own shutoff valve that will shutoff water flow when a leak springs.
Regarding using a single 30A breaker you will protect the output of the phase coverter and perhaps the conductor depending on its size.

[Matt Hutchinson]

Ok, that's what I thought. Good deal. I may actually be gettin' this stuff figured out. Woohoo!

Thanks again!

Hutch

P.S. I am sure I will think of some more questions. I will post a wiring diagram just as a confirmation step, cuz I don't want to overlook anything.

P.P.S Scott, I don't know of any plant closings, but there is a surplus industrial warehouse which has a lot of this kinda stuff. I definitely will have to go take a look and see what's available. Who know, maybe I will get lucky!

[Rollie Meyers]

Ok, that's what I thought. Good deal. I may actually be gettin' this stuff figured out. Woohoo!

Thanks again!

Hutch

P.S. I am sure I will think of some more questions. I will post a wiring diagram just as a confirmation step, cuz I don't want to overlook anything.

P.P.S Scott, I don't know of any plant closings, but there is a surplus industrial warehouse which has a lot of this kinda stuff. I definitely will have to go take a look and see what's available. Who know, maybe I will get lucky!

A used 3Ø loadcenter or panelboard would be a good way to distribute your output, just make sure you don't get a obsolete panel even if it's full of breakers, the cost of obsolete circuit breakers will make most folks choke.

Zinsco/Sylvania, Federal Pacific Electric (FPE) are besides being the most reviled names in the electrical industry are very costly to buy replacements for. I-T-E Pushmatic was avail in 3Ø but quite rare, Cutler-Hammer CHB is also obsolete but the later C-H PB panelboards accept CHB bolt-on and the still manufactured type CH plug-in breakers, the list can go on for a bit.

[Thomas Syrotchen]

Good point Rollie, on the other side, Allen Bradley products are generally easy to come buy and very common in industrial settings. While pricey new and likely a little more costly used, they have a huge distribution network that makes them easy to replace. Just keep in mind you won't find them at a local home center, but a distributor should be easy to find.

[Rollie Meyers]

Good point Rollie, on the other side, Allen Bradley products are generally easy to come buy and very common in industrial settings. While pricey new and likely a little more costly used, they have a huge distribution network that makes them easy to replace. Just keep in mind you won't find them at a local home center, but a distributor should be easy to find.


Allen-Bradley does not build circuit breakers or panels they used I-T-E, GE, and Westinghouse/Cutler-Hammer breakers for their equipment.

[Thomas Syrotchen]

Rollie,
I wouldn't know if they manufacture their own equipment or not. However, they offer several lines of breakers most Din rail mounted designed for Motor Control Centers, UL listed and perferct for this application. Since we are talking about purchasing a panel from a plant shutdown, purchasing a prebuilt MCC with Allen Bradley breakers in it would be something I would certainly recommend. We use a lot of AB equipment for the very reason you mentioned availability. If a plant is closing, your likely to find din rail mounted stuff like this
http://www.ab.com/industrialcontrols/products/control_circuit_and_load_protection/circuit_breakers/1489.html
or this
http://www.ab.com/industrialcontrols/products/iec_motor_control/.

Their 140M would be perfect for for protection of branch motor circuits the second link.
I assume you were refering to just a standard subpanel and dropping it in the wall, which in that case I believe you are correct AB doesn't offer anything but Allen Bradley does offer an extensive line when it comes to motor protection and branch circuit protection.
Since the phase coverter is already going to have an enclosure that will likely have to be surface mounted, if it were me, I'd look to pick up an enclosure with disconnect, molded case breaker, and distribution block in the can and run the output of the phase converter right into the enclosure. The advantage is if you decide to move, the panel comes off the wall and away you go. Drop a Subpanel in the wall, now its part of the structure and the buyer may argue that your removing wiring.

Tom

[Matt Hutchinson]

Interesting thought. I hadn't even thought about the "removing wiring" issue. Even so, can't a person still surface mount just about any box?

Hutch

[Thomas Syrotchen]

Matt,
You can buy them either way, the flush mount type have oversized covers to hide gaps between the panel and drywall. You can surface mount either but a flushmount on top of the drywall looks funny. However, you are much more likely to find 3 phase panels that don't have oversized covers.
I think the confusion on my statement on Allen Bradley is I assumed a generic panel, and at one point a loadcenter and panelboard was mentioned which is likely what Rollie was refering too. Typically, a Motor Control Center (MCC) on the industrial side will hit a fusable disconnect, then a distribution block, Circuit protection, Starting device, overload and then out to a motor. Loadcenters are normally used as feeders to the MCC however, using a loadcenter or panelboard will work just fine as well. There are some difference in sizing breakers depending on which way you go.

[Rollie Meyers]

DIN rail breakers are listed as supplementary overcurrent protection, they are not for general purpose use, use a loadcenter or hang a gutter & mount safety switches off it, a Motor Control Center (MCC) is a nice idea if you can snag one cheap but will use more real estate over a panel, + if one ever needed a different bucket for a MCC, be prepared to pay plenty of dough for one.

[Matt Hutchinson]

Ok, so is this the kind of box and breaker I need? Also, am I correct in thinking that if I get a switch like this:
http://grizzly.com/products/Magnetic-Switch-3-Phase-220V-Only-3-HP/G4673
that I would no longer have to worry about fuses to protect the motors?

Thanks

Hutch

[Rod Sheridan]

Hi Matt, fuses aren't for motor overload protection, just short circuit protection.

A motor will require a starter with a thermal overload relay (either a magnetic or manual starter).

I can't open the link you sent, however if it's a mag starter with the required current range, you simply set it at the nameplate current for your motor and it will provide overload protection.

Regards, Rod.

[Thomas Syrotchen]

Matt,
The device you sent has both a contactor and overload relay in it as well, it will not provide short circuit protection and I would still recommend the use of a breaker or fuse in the circuit.
In a motor circuit their are two types of protection, short circuit protection and overload protection. Overload protection is exactly what it sounds like, it prevents you from loading up a motor for two long a period. In essence, if the current through a motor exceeds 105% for a period of time in the seconds the device will trip like a breaker. That period of time is long enough such that the motor can pull enough current to startup and get up to speed. Hence the requirement for the current draw to be over a period of time. Using just overload protection can be dangerous if you had a short to ground, a the circuit could pull several times the rated current for several seconds exceeding the conductor rating and doing damage as well. So, a fuse or breaker is installed to limit the current in the event of a short circuit. Both methods are required to help protect equipment and the circuit.
As I explained in my previous post, the standard method for wiring a motor circuit is to first hit a short circuit protection device either a breaker or fuse block, then a contactor and finally an overload device that will open the contactor in the event the overload device is tripped. I would suspect a 5HP machine may already have an overload device in the circuit.
If you'll notice in the link you provided at the top of the contactor its labeled L1, L2, L3 this is where your line power is applied. On the bottom its labeled T1, T2, T3 which is where the leads for the overload relay are connected. On the overload relay you see in an adjustment to limit the current to the motor. On the bottom of the overload relay you see another set of T1, T2, and T3 which is where you would connect the motor. If you take a look at your machines, if you find overloads in them then you would not need to add that switch with an overload, just short circuit protection. You may want to call the manufacturer and find out as well. A reset button is another indication that the device has some form of circuit protection again, check with the manfuacturer to determine the exact form of protection its providing.

[Thomas Syrotchen]

Here is an overload relay by itself

http://www.ab.com/industrialcontrols/products/iec_motor_control/overload_relays/E1_plus.html

[Matt Hutchinson]

Alright, I suppose I should have done a better job of wording the question.

If I use a breaker box like the one pictured (powered by the RPC), with a breaker sized according to the gauge wire run to the motor (or smaller, but not smaller than the load amperage), then run to the machine through turn-lock plugs (all of them have starters, but I'm not sure about thermal overload), then into a mag switch, will that cover all the bases?

Hutch

P.S. The machines I am powering are a 5hp 14" RAS, a 1/2 hp jointer, and a 3 hp Unisaw. (All Rockwell)

[Rollie Meyers]

Ok, so is this the kind of box and breaker I need? Also, am I correct in thinking that if I get a switch like this:
http://grizzly.com/products/Magnetic-Switch-3-Phase-220V-Only-3-HP/G4673
that I would no longer have to worry about fuses to protect the motors?

Thanks

Hutch

That SQ D QO panel would be a good choice, the one pictured is a older one made before SQ D went to building junk panels, the circuit breaker pictured is a Westinghouse* & it will not fit the panel pictured, that mag starter shown in your link is one to avoid, as is anything from that purveyor of cheap Chinese throwaway junk.

* Eaton bought the Westinghouse electrical line & merged it into their Cutler-Hammer unit.

[Matt Hutchinson]

Yeah, the compatability issue could prove interesting, but if that particular panel appears good then I will see if can scare up usable breakers.

As for the cheap chinese mag switch, do you know where I look to get a different make? I have been doing searches, and have not been having good luck.

Hutch

[Thomas Syrotchen]

I'd echo Rollie's comments on grizzly starter, I wouldn't use it either. First thing I did when I bought my tablesaw a few years back was replace one of those type starters with an E-Bay purchased AB starter. I think I paid $20 plus shipping for it. Did the same thing with my planer as I just want my stuff to work all the time.

As far as the solution goes, it sounds like you have the concept down, feed the starter from your breaker panel. Its a breaker panel or fuses, both is redundant. I only suggested fuses as a less expensive option to a breaker. As far as overloads go, if all the equipment has starters, then there's a fair chance they may have overloads already wired in and sized by the manufacturer. If you want to open up the starters and take a picture of the contactor we might see the overload as well and can help you identify it.

Tom

[Rollie Meyers]

Yeah, the compatability issue could prove interesting, but if that particular panel appears good then I will see if can scare up usable breakers.

As for the cheap chinese mag switch, do you know where I look to get a different make? I have been doing searches, and have not been having good luck.

Hutch

SQ D QO breakers have been around a long time, so should be EZ to get them if you search eBay try QO315, QO320, QO330, avoid QOB as they are bolt-on & not compatible w/ the panel you pictured.

If you look for starters, look for SQ D, Allen-Bradley or Siemens/ Furnas ESP 100 which is a good choice due the fact that ESP 100's have adjustable overload relays & no need to buy heater coils one just needs to be aware of the adjustment range of the O/L relay & that the FLA of your motor fits within that range, SQ D calls their O/L relays of the same type Motor Logic & Allen-Bradley also has the same. While I am at it Cutler-Hammer Freedom series starters use heater packs & are current production items, Cutler-Hammer Citation series (my personal favorite) is obsolete & parts can be dear, list price for heaters is $80.00 ea when you can buy others for $12.00 ea, which is not a problem for me as have a stash of starters & parts for them.:) On a last note a Westinghouse (now Cutler-Hammer) A200 is current production also so is also a option, I would stay away from obsolete gear as parts can be hard to get & if one does find them they can be expensive.

[Thomas Syrotchen]

Matt,
Square D, Allen Bradley and Siemens all have excellent websites where you can search for part #'s etc. If you use E-Bay their sites will help you figure out what a part # really is if that is all that is listed. As far as sources, there are a number of websites that source industrial parts, surplus, new and used. A quick google search for PLC parts will get you a couple of sites. If you would rather buy new locally, that may get tricky depending on your local contacts as AB and Siemens are likely wholesale distributors. Allen Bradley will likely have a single distributor in the area. Square D can likely be found at most electrical distributors and I belive Grainger may carry them as well.

[Matt Hutchinson]

Again, the information y'all have provided is very helpful. As for the starters, I am not sure that I will need any, but a few good contactors appears to be in order from what you have said.

There are a couple sources here locally where I might be able to walk in and look at surplus parts, etc... Right now I am out of town, and my digital camera cable has gone missing, but I will try to get a picture of the starters to you guys. After a quick look on OWWM I think they probably have thermal overload.

As for the mag switch I gave a link for, I really like the thought of have protection against a machine kicking back on in case of a power outage. Do machine starters usually include this type of feature?

Thanks!

Hutch

[Thomas Syrotchen]

Matt,
They aren't doing any rocket science with the contactor, all they do is use the Normally Open aux contact on the starter to hold it in. It is simple to do if you have an aux contact and wire it correctly. Essentially, you use a momentary device to power the contactor. Then take the coil power, pass it through a normally closed set of contacts for a shutoff switch and the normally open set of aux contacts on the contactor. The momentary on switch will power the contactor initially, then the aux contacts close and maintain power to the contactor until power is removed or the shutoff switch is pressed which breaks the maintiained power on the coil.

[Matt Hutchinson]

So if I understand you correctly, you are saying that in the event of a power outage the saw would not jump back on (this is built into the starter)? So I might as well save a few bucks and use the switches that are already in place, right? Thanks.

Hutch

P.S. I can get the QO320 breakers easily right now. Should I plan on running a circuit for each machine, or just one for all of them? I would think a 20A breaker would easily handle multiple machines running at once. Is there really any big advantage to running each on its own circuit, or is that a silly way to spend my limited resources?

[Thomas Syrotchen]

Matt,
If you are running them at 220V, I come up with approx 35A for a 10HP phase converter. 20A at 220 would barely handle a 5HP motor and likely trip on startup.

As far as the starter on your equipment goes and not restarting, that depends on how its wired, its easy to wire that way if the contactor has a normally open set of aux contacts, that would depend though on how the manufacturer wired the contactor, as it can be wired to return power to the equipment after a power loss as well.

As far as one breaker feeding all motors I would check with your local inspector to see if that would meet code. The reason for a breaker is to limit current to a motor and circuit to prevent damage. If you size the breaker at 35A to handle everything, your virtually providing no real protection to the smaller motors. A 1/2 HP motor should be protected at approx 3A. Running a single breaker would allow 10 times that current to hit the motor. If I had to choose between installing one breaker for all the equipment or waiting until I had a little more cash to buy breakers, I'd wait until I could buy breakers for each piece of equipment.

[Matt Hutchinson]

Oh, see, on the single phase sub-box that will power the converter I will have a 50-60A breaker. I meant the 3 phase breaker box from which individual machine circuits will be run. If I need a 30A for the 5 hp that's fine, cuz those are available as well.

Here's the long range plan for what 3 phase motors I KNOW I will need to power. What breaker size should I use?

3 hp - Tablesaw
1/2 hp Jointer, (probably upgraded to 1.0 HP in the future)
5 hp Radial Arm Saw
3 hp Lathe

Hutch

[Alan Bienlein]

Oh, see, on the single phase sub-box that will power the converter I will have a 50-60A breaker. I meant the 3 phase breaker box from which individual machine circuits will be run. If I need a 30A for the 5 hp that's fine, cuz those are available as well.

Here's the long range plan for what 3 phase motors I KNOW I will need to power. What breaker size should I use?

3 hp - Tablesaw
1/2 hp Jointer, (probably upgraded to 1.0 HP in the future)
5 hp Radial Arm Saw
3 hp Lathe

Hutch

Remember Matt that the breaker doesn't protect the motor it protects the wiring. The motors should have some type of current limiting device to protect the motor. Some have it built in like when you see the red button on them that you press to reset if it trips. Look at the nameplate rating to get the amps to size your wire and size the breaker to protect the wire.

[Matt Hutchinson]

Well, that's what I assumed, but I like to double check on stuff like this. :rolleyes: Also, I just didnt' know how much I needed to consider startup amperage in circuit sizing.

And part of the issue is what I have available. Since I don't have many smaller amperage circuit breakers available, can I oversize the breaker if the motor has thermal overload protection, or is it absolutely necessary to keep them sized close to each other? (I know using oversized wire doesn't really come into play, cuz it's the breakers/fuses that are important. But with thermal overload protection I am unsure of what I can/should/shouldn't try to get away with.)

Hutch

[Thomas Syrotchen]

Matt,
There are tables in the NEC that have suggested values as well as most manufacturers publish information on what values to use. If you don't have access to that info, I'd start by sizing by breaker at 150% FLA (FLA is on the motor nameplate). If you use 150% though, you need to ensure that everything in the circuit is rated for that current load which will include the manufactures starter. If anything is rated below 150% then use that value as your breaker size.

For example, FLA for my 5HP is 22.5A, and I find the label on my contactor that says it has an inrush current rated for 25A. 150% of my FLA is 33.75A but I should choose the 25A value to protect the contactor. Hopefully the equipment manufacturer wouldn't put you in a situation like that and the contactor would be rated to handle a current load above that level. Most contactors will likely be rated above that level, but I would still check. Now lets say that the contactor is rated at 45A inrush current. I'm still limited by the 10 Guage conductor at 30A. So I would choose 30A.

There was a reference to the NEC code section earlier on how to select sizes etc. There are a lot of rules around this, and it would certainly be of value to read that section.

[Alan Bienlein]

Well, that's what I assumed, but I like to double check on stuff like this. :rolleyes: Also, I just didnt' know how much I needed to consider startup amperage in circuit sizing.

And part of the issue is what I have available. Since I don't have many smaller amperage circuit breakers available, can I over size the wire and breaker if the motor has thermal overload protection, or is it absolutely necessary to keep them sized close to each other? (Again, a confirmation of what I think I already know but want to double check.)

Hutch

You usually increase wire size if the length of the run dictates it because of voltage drop. Increasing the wire size when its not needed just cost you more money. Just make sure to size the breaker to protect the size of the wiring your using.

If it were me I would buy what I need breaker wise and try too stick with the nameplate ratings. Sometimes you can get to large of a breaker for a circuit and what would trip a correctly sized breaker might not trip the larger breaker which could become a hazard.

[Matt Hutchinson]

Yeah, I will now take to time to read the NEC info. Prior to this I don't think understood enough of the terminology to be able to make it through that kind of information. I will check it out now.

Hutch

[Rollie Meyers]

Matt,
There are tables in the NEC that have suggested values as well as most manufacturers publish information on what values to use. If you don't have access to that info, I'd start by sizing by breaker at 150% FLA (FLA is on the motor nameplate). If you use 150% though, you need to ensure that everything in the circuit is rated for that current load which will include the manufactures starter. If anything is rated below 150% then use that value as your breaker size.

For example, FLA for my 5HP is 22.5A, and I find the label on my contactor that says it has an inrush current rated for 25A. 150% of my FLA is 33.75A but I should choose the 25A value to protect the contactor. Hopefully the equipment manufacturer wouldn't put you in a situation like that and the contactor would be rated to handle a current load above that level. Most contactors will likely be rated above that level, but I would still check. Now lets say that the contactor is rated at 45A inrush current. I'm still limited by the 10 Guage conductor at 30A. So I would choose 30A.

There was a reference to the NEC code section earlier on how to select sizes etc. There are a lot of rules around this, and it would certainly be of value to read that section.

Circuit breakers & fuses for motors are sized at 175% to 800% or more depending on the type of circuit breaker/fuse & motor, a motor starter or O/L protector provides overload protection & the fuse or circuit breaker provides short circuit protection, for this reason you could have 12 AWG on a 50A circuit breaker.(Normal rules limiting 12 AWG to 20A do not apply to motors).

For example a 5 hp single phase motor w/ a FLA of 22A, permission is given to use table 310-16 which lists 12 AWG in the 75° column at 25 amperes, table 430-152 lists single phase motors using a inverse time circuit breaker @ 250% of full load current 22A X 250% = 55A, next standard circuit breaker is 60A, upsizing to the next standard size is allowed up to 800A. Size conductor to the minimum, fuse or circuit breaker to the max, & your code compliant.

[Rick Christopherson]

Here's the long range plan for what 3 phase motors I KNOW I will need to power. What breaker size should I use?

3 hp - Tablesaw
1/2 hp Jointer, (probably upgraded to 1.0 HP in the future)
5 hp Radial Arm Saw
3 hp Lathe

HutchI think you might be getting some misleading information because several people are citing amperages for single phase motors. Because these are 3-phase motors, they will all draw less than 15 amps. The 5 hp RAS will have approximately 14 amps FLA, and technically should be on a 20 amp circuit, but since it is unlikely to ever fully load this motor, it could operate from a 15 amp circuit. All of the remaining motors will be well below 15 amps.

[Rick Christopherson]

For example a 5 hp single phase motor w/ a FLA of 22A, permission is given to use table 310-16 which lists 12 AWG in the 75° column at 25 amperes, table 430-152 lists single phase motors using a inverse time circuit breaker @ 250% of full load current 22A X 250% = 55A, next standard circuit breaker is 60A, upsizing to the next standard size is allowed up to 800A. Size conductor to the minimum, fuse or circuit breaker to the max, & your code compliant.Rollie, this is dangerous information to be presenting on a forum like this. First off, there is no Table 430.152 in any of the code versions I have (2008 and 2005 for certain, and I am pretty sure it is not in my 1998 either), so I can not be certain how this information relates to motors, but I suspect you are refering to a similar table 430.72. However, that table applies to control wiring for a motor, so its reference here is inappropriate.

Article 430.6 specifically states that supply conductors for motors follow the tables referenced in 310.15

[Rollie Meyers]

Rollie, this is dangerous information to be presenting on a forum like this. First off, there is no Table 430.152 in any of the code versions I have (2008 and 2005 for certain, and I am pretty sure it is not in my 1998 either), so I can not be certain how this information relates to motors, but I suspect you are refering to a similar table 430.72. However, that table applies to control wiring for a motor, so its reference here is inappropriate.

Article 430.6 specifically states that supply conductors for motors follow the tables referenced in 310.15

430.52 is the table 1 digit that did not belong.

[Rick Christopherson]

430.52 is the table 1 digit that did not belong.This table and its preceding section dictate the overcurrent protection for the circuit, but do not dictate the conductor size.
....... for this reason you could have 12 AWG on a 50A circuit breaker.(Normal rules limiting 12 AWG to 20A do not apply to motors).No, this section does not permit using overcurrent devices that exceed the ampacity of the conductor. It is simply indicating that you can oversize the circuit to allow for high in-rush current. You still must comply with the data in table 310.16
NEC 430.6 Ampacity and Motor Rating Determination.
The size of conductors supplying equipment covered by Article 430 shall be selected from the allowable ampacity tables in accordance with 310.15(B) or shall be calculated in accordance with 310.15(C). Where flexible cord is used, the size of the conductor shall be selected in accordance with 400.5. The required ampacity and motor ratings shall be determined as specified in 430.6(A), (B), and (C).So No, you cannot put 50 amp breakers on #12 wire.

[Rollie Meyers]

This table and its preceding section dictate the overcurrent protection for the circuit, but do not dictate the conductor size.No, this section does not permit using overcurrent devices that exceed the ampacity of the conductor. It is simply indicating that you can oversize the circuit to allow for high in-rush current. You still must comply with the data in table 310.16So No, you cannot put 50 amp breakers on #12 wire.

If the motor has O/L protection, the fuse or circuit breaker is for short circuit protection so it can be "oversized" for a motor load but you must size the wire for the load, as long as the wire can handle the FLA there is nothing wrong with that method, being conservitive is OK too as a 5 HP 3Ø motor will do fine on a 20A 240V circuit if it is not a hard starting load.

[Rick Christopherson]

If the motor has O/L protection, the fuse or circuit breaker is for short circuit protection so it can be "oversized" for a motor load but you must size the wire for the load.....You have said this several times, but you have not provided the citation that permits you to override 430.6 quoted above. These do not fit the requirements to be classified as tap conductors. If I am wrong, would you please provide the citation that permits you to size a conductor lower than its upstream OCPD.

[Thomas Syrotchen]

A little clarification to remove some confusion the example I provided was not intended to represent actual numbers, simply an idea of the process of how to determine size. Rick is correct in stating that 22.5A would not be typical of a 3 phase 5HP motor, it was intended as such to show mulitiple items may limit the size of overload protection, I had to have a large number to exceed the 30A threshold, in retrospect, probably confusing and I should have clarified up front.

To ensure I don't mislead anyone either based on early statements, to be compliant with the NEC, conductor sizing should be based on the tables from the NEC at 125% minimum and not on the Nameplate FLA. Overloads should be sized based on the nameplate FLA and sized at 115% - 125%. Normally the overload will be sized at 115%, unless the motor has a temp rise of 40C or a service factor of greater than 1.15 allowing the overload to be sized at 125%.

Rick, thanks for the reminder, really providing rule of thumb info can be misleading and get people in trouble.

I do believe Rollie is actually correct on oversizing the breaker as the overload must be sized at 115% to 125% effectively limiting the current and allowing the short circuit protection to be oversized. Mike Holt supports that statement http://www.mikeholt.com/mojonewsarchive/EC-HTML/HTML/Motor_Calculations_-_Part_1~20030303.htm The link below I believe supports that statement as well, as I believe some of the suggested Short Circuit Protection sizes exceed conductor rating.

Matt,
Here is a great cheat sheet for you
http://www.bussmann.com/library/docs/spd02/SPDSection12.pdf