What size power cord for 220v 5 hp 1ph motor?

[Don Buck]

What would be recommended for a power cord to power a 5 hp, single phase 220v planer drawing 25 amps full load? Wiring hook-up requires 2 hot lines and a ground. Delta manual states the circuit should be "no less than #12 wire protected by a 20 amp time lag fuse". I wired the circuit with #6 with a 50 amp breaker to handle the surge.

I can't seem to find a power cord at my BORG heavier than #10 2+g. If I'm not mistaken, isn't #10 rated for 30 amp circuits? The power cord will attach the circuit via a 50 amp 230v plug and the cord will be about 8' in length.

What are others using/recommending?

Don

[Kirk Poore]

The breaker protects the line up to the outlet. The #10 wire should be fine, since its 30 amp capacity is larger than your 25 FLA motor. A machine that big should have a starter or other overload protection on it to stop it if for some reason it pulls more than 25 amps for an extended period of time.

Kirk

[dave toney]

#10 wire is just fine.
The wire going to the outlet from the breaker is probably #10 and is likely to be run longer than the cord will be.
Also, 220 volts "divides" the amps between the 2 110 volts hot wires, 12.5 amps per wire.

Dave

[mreza Salav]

#10 wire is just fine.

Also, 220 volts "divides" the amps between the 2 110 volts hot wires, 12.5 amps per wire.

Dave

that is simply NOT correct. There is no such thing as dividing of amp's between legs. When it says 25 amps it is 25 amps.

[Clint Olver]

I have a similar planer (20" 5Hp), and it is on #10. In fact, everything that is 220V in my shop is on #10.

C

[Joe Angrisani]

....Also, 220 volts "divides" the amps between the 2 110 volts hot wires, 12.5 amps per wire....

Yeah...wow. This is wrong and kinda scary. You might want to check the cords you've put on your machinery, Dave.

[Doug Palmer]

National Electrical Code (NEC) requires a that the cable size for a motor be 125% of the rated full load amps of the motor. The NEC also specifies that if you are not specifically given the FLA then you use the chart provided in the code book. A single phase 5 hp motor operating at 230volt is rated at 28 FLA in the chart. If your documentation indicates 25 amps, you may use that value instead of the chart value. 25 x 1.25 = 31.5 amps. Your cable size should be sufficient to handle 31.5 amps. A #10 gauge wire is rated for 35 amps and is the recommended cable size for your motor. You are wise to have a 50 amp circuit, as a smaller circuit could give you nuisance trips.

You should not use a #12 wire if the motor is truely a 5 hp. Of course a lot of the motors we see on power tools are said to be bigger than they truely are. Most of the asian made motors are rated at peak horsepower, not continuous hp. If the FLA is 25 amps, you are dealing with a true 5 hp motor.

Use the #10 and you will be safe and meet the appropriate NEC and NFPA (National Fire Protection Association) requirements.

FYI, I am a Licensed Master Electrician and Electrical Engineer with 28 years experience.

[Don Buck]

Thanks Doug and others, I feel safe to go ahead and use the #10 wire.

Don

[Steve Schoene]

Actually, I think the manufacturer's instructions, if they are as the o.p. indicated in the first post, trump the Code in most cases, meaning he could have, had he desired use a 20 amp circuit in the walls. Manufacturer's instructions would be similar to having a specific situation engineered. But there is absolutely nothing wrong with using a more conservative approach. I wouldn't recommend using the 20 amp circult since most all other 5 hp. motors would require a 30 amp circuit on no. 10 wire.

But, going to number 6 wire is serious overkill with virtually no benefit I would think unless there were major factors that would call for derating the wiring, such as bundling or exceedingly long runs, neither of which were hinted at. The makers of the code, and the manufacturer's instruction both are fully aware of start up surges and those are already factored into the specification of necessary circuit ampacity.

[Doug Palmer]

Manufactures instruction never trump the NEC unless it is more stringent or satisfy a specific NEC qualification. That is the whole purpose of the NEC, to keep companies or individuals from unsafe installation.

[John McClanahan]

Your cable size should be sufficient to handle 31.5 amps. A #10 gauge wire is rated for 35 amps and is the recommended cable size for your motor. You are wise to have a 50 amp circuit, as a smaller circuit could give you nuisance trips.

Doug, Can you explain this in better detail? These types of questions are asked frequently. You wouldn't use 14 gauge wire with a 30 amp breaker. Does it require motor overload protection at the motor?

I'm not calling you out on this! I would just like to more on NEC requirements for feeding and protecting motors, like found on shop equipment, from someone with your knowledge and experience.


John

[dave toney]

Yeah...wow. This is wrong and kinda scary. You might want to check the cords you've put on your machinery, Dave.

I stand corrected!
I guess I was thinking about the difference in amps on dual voltage motors, in which the amps do drop by half when voltage is doubled.
Most of my machines are three phase and don't have cords.
Sorry for any confusion.
Dave

[Doug Palmer]

Actually, you bring up a very good point. Yes there should be motor protection if we are going to use a #10 guage wire on a 50 amp circuit. I do not have my code book in front of me, but will review it. There are some provisions for lighter cables for loads that are not permanently attached. I do not think we are required to have motor overload protection in this case, but will need to review the specific code for this application. For example, you can plug #16 gauge lamp into a 20 amp circuit, but you must run #12 wire to the receptacle. I do not want to say positively until I review the specific code. We do need a #10 wire for the motor, the question remains since we are in a 50 amp receptacle do we need to look at sizing for 50 amps? I am fairly sure the answer is no, but will find the specific code to be sure. The motors nominal load will be well below the size of the #10, so the only potential problem is a short in the motor. Typically a short will result in an instantaneous surge in current that will still trip the 50 amp breaker. If the motor pulled high (but not short circuit level) amps for an extended time, it is expect that the motor will burn up, causing either a short or open circuit because the motor is the weak link not the wire. Thereby, not being a significant fire risk. In fact code recommends a 60 amp circuit breaker for a 5 hp 230v motor, but with overload protection.

Nice question, I will review and provide code reference to be clear. In fact, if the motor has built in protection at a lower current level, the #12 wire might actually be approvable. This should be identified in the documentation.

[Doug Palmer]

Dave,

I have reviewed the NEC and section 430.42(C) discusses Cord-and-Plug Connected motor loads on General-Purpose Branch Circuit, which is what we are dealing with.

The code states that "Where a motor is connected to a branch circuit by means of an attachment plug and receptacle and individual overload protectionis ommitted ..... shall not exceed 15 amps at 125 volts or 250 volts. Where individual overload protection is required ..... the overload device shall be an integral part of the motor or of the appliance."


Bottom line is yes, in this case the motor should have overload protection. As I recall most (if not all) of the larger table saws have a thermal overload built into the motor. There is a small reset button on the back end of the motor. I know mine does. If the system is home made with a motor without a thermal trip unit, an overload will need to be added integral to the motor circuit. For example, I built my own cyclone dust collector and have the 5 hp motor starting through a motor starter which contains the overload protection.

I hope that helps.

Please note that the 2011 NEC code book is almost 900 pages of small print on 8 1/2" x 11" paper. I will be happy to look up any code for a specific application, but it is near impossible to know all code off the top of my head.

[Jason Roehl]

Doug, that says "...shall not exceed 15 amps at 125 volts or 250 volts". We're talking about a 5HP, 250V motor pulling 25 FLA. And, is Section 430 applicable to a home shop, or an industrial facility? Is the OP's locale even using the 2011 NEC as their electrical code?

This happens all too often here, where people come, quote "code", make it sound like the OP is doing something dangerously unsafe, when the reality is that the code quoted doesn't even remotely apply because it's for industrial setups. Don't get me wrong, I'm not recommending he use a homemade lamp cord extension cord, but he was debating whether to use something heavier than 10-AWG for an 8' power cord. I regularly use a 100' 10-AWG/SJ 240V extension cord for a 7.5HP 12" belt sander for wood floors. I've tripped 30A breakers before using it, too, but the cord has never even felt warm.

10-AWG should be PLENTY of cord for such a short run. If you're really concerned, go to an electrical supply house and ask for SJ cord and the appropriate twist-lock connectors.

[Doug Palmer]

Doug, that says "...shall not exceed 15 amps at 125 volts or 250 volts". We're talking about a 5HP, 250V motor pulling 25 FLA. And, is Section 430 applicable to a home shop, or an industrial facility? Is the OP's locale even using the 2011 NEC as their electrical code?

This happens all too often here, where people come, quote "code", make it sound like the OP is doing something dangerously unsafe, when the reality is that the code quoted doesn't even remotely apply because it's for industrial setups. Don't get me wrong, I'm not recommending he use a homemade lamp cord extension cord, but he was debating whether to use something heavier than 10-AWG for an 8' power cord. I regularly use a 100' 10-AWG/SJ 240V extension cord for a 7.5HP 12" belt sander for wood floors. I've tripped 30A breakers before using it, too, but the cord has never even felt warm.

10-AWG should be PLENTY of cord for such a short run. If you're really concerned, go to an electrical supply house and ask for SJ cord and the appropriate twist-lock connectors.
The code is for either residential or industrial. The exact point is that since the motor pulls more than 15 amps, it is required to have overload protection integral to the motor. Of course a #10 guage wire wouldn't feel warm on a 30 amp circuit. It is rated for 35 amps as stated in an earlier post. Further it is the recommended cable size as stated in an earlier post. It is not a simple guess or a number grabbed out of the air. It really doesn't matter if your area is governed by the 2011 NEC or not, you would be foolish to ignore the code. It is written to provide a safe installation and it is sanctioned by the NFPA. There are many things that you can do that are not safe and get by with it multiple times. That does not make it a wise choice to ignore them. I didn't write the code. You are free to make your own choices,, maybe you are smarter than those that did.

[Chris Friesen]

Doug, that says "...shall not exceed 15 amps at 125 volts or 250 volts". We're talking about a 5HP, 250V motor pulling 25 FLA. And, is Section 430 applicable to a home shop, or an industrial facility?

Read his full quote. The 15A bit applies where individual overload protection is omitted. Anything above 15A requires individual overload protection, ie. on the tool itself. This could be right on the motor, or could be built into the mag switch.

Whether section 430 applies is an interesting question. I'm up in Canada so things are a bit different, but the code is pretty similar. On the Canadian woodworking forum an electrician happened to be taking a course and spoke with the instructor about it. The instructor's take was that a receptable in a typical homeowner shop doesn't become a motor circuit just because a motor is plugged into it. Rather, it's considered a general-purpose circuit. If the machine is hardwired to the wall then it becomes a motor circuit and section 430 would apply.

[Steve Schoene]

I think that you can be quite confident when a US based manufacturer writes an instruction manual it's engineers, consultants and lawyers have made darn sure that those instructions meet the applicable code requirement. The liablitity potential would be too large for them not to take serious pains to be correct for their specific circumstance. And, knowing the product, they can make the effort to fully review the situation to correctly determine which are the relevant code requirements.

[Doug Palmer]

Read his full quote. The 15A bit applies where individual overload protection is omitted. Anything above 15A requires individual overload protection, ie. on the tool itself. This could be right on the motor, or could be built into the mag switch.

Whether section 430 applies is an interesting question. I'm up in Canada so things are a bit different, but the code is pretty similar. On the Canadian woodworking forum an electrician happened to be taking a course and spoke with the instructor about it. The instructor's take was that a receptable in a typical homeowner shop doesn't become a motor circuit just because a motor is plugged into it. Rather, it's considered a general-purpose circuit. If the machine is hardwired to the wall then it becomes a motor circuit and section 430 would apply.
Yeah, Chris, we have had that argument many times in the past. That is why the NEC now includes subsection 430.42(C), which is entitled "Motors on General-Purpose Branch Circuits - Plug and Cord Connected", which was added in 2008.

[Kent A Bathurst]

....FYI, I am a Licensed Master Electrician and Electrical Engineer with 28 years experience.

Doug:

1] welcome to the Creek
2] thanks for a dispassionate, clear analysis, response, and subsequent clarifications
3] you may not quite realize what you just opened yourself up for........thanks again :D

[Jason Burt]

I stand corrected!
I guess I was thinking about the difference in amps on dual voltage motors, in which the amps do drop by half when voltage is doubled.
Most of my machines are three phase and don't have cords.
Sorry for any confusion.
Dave

Or maybe you were thinking that the total line length is double what people typically think?

[Robert Engel]

National Electrical Code (NEC) requires a that the cable size for a motor be 125% of the rated full load amps of the motor. The NEC also specifies that if you are not specifically given the FLA then you use the chart provided in the code book. A single phase 5 hp motor operating at 230volt is rated at 28 FLA in the chart. If your documentation indicates 25 amps, you may use that value instead of the chart value. 25 x 1.25 = 31.5 amps. Your cable size should be sufficient to handle 31.5 amps. A #10 gauge wire is rated for 35 amps and is the recommended cable size for your motor. You are wise to have a 50 amp circuit, as a smaller circuit could give you nuisance trips.

You should not use a #12 wire if the motor is truely a 5 hp. Of course a lot of the motors we see on power tools are said to be bigger than they truely are. Most of the asian made motors are rated at peak horsepower, not continuous hp. If the FLA is 25 amps, you are dealing with a true 5 hp motor.

Use the #10 and you will be safe and meet the appropriate NEC and NFPA (National Fire Protection Association) requirements.

FYI, I am a Licensed Master Electrician and Electrical Engineer with 28 years experience.This is correct Take it to the bank!

Yeah, Kent he needs to be ready for some PM's.......

I had a licensed electrician run #12 wire to my 5HP compressor on a 30A breaker. I questioned it right from the start.
Well, after intermittent (not heavy) use the capacitor went.
When I replaced the capacitor I re-ran #10.

On a machine that big you're not moving it around instead of a plug you can wire it straight to the switch or use a cutoff box if you want.
Or you can make up your own cord with #10 wire and a 30 A twist lock plug.

[Rollie Meyers]

#10 wire is just fine.
The wire going to the outlet from the breaker is probably #10 and is likely to be run longer than the cord will be.
Also, 220 volts "divides" the amps between the 2 110 volts hot wires, 12.5 amps per wire.

Dave

110 and 220V no longer exist as a supply voltages, unless your in the part of the world that uses 50 Hertz and then it's line and neutral, 110V is used on UK building sites, stepped down from 240V, each leg is 55V. 25A at 240V is still 25A, not 12.5A per leg.


24A is the max for a 30A circuit, to maintain 80% of circuit capacity.

[Shawn Walsh]

Would wire size need to be adjusted if running a 5hp 220v motor on 208v single phase? I have 208v three phase service and have a couple 5hp single phase machines to hook up. Thanks for the thorough answers so far.

[Art Mann]

Manufactures instruction never trump the NEC unless it is more stringent or satisfy a specific NEC qualification. That is the whole purpose of the NEC, to keep companies or individuals from unsafe installation.

The NEC isn't a legally binding document. It is a guideline put out by the NFPA, which is a private organization. It is up to local governments as to whether to use it and which version to apply. The more important standards to apply in this case is UL or CSA standards.

[Chris Padilla]

Folks, this thread dates back to 2011. Just an FYI.

[Mike Heidrick]

Would wire size need to be adjusted if running a 5hp 220v motor on 208v single phase? I have 208v three phase service and have a couple 5hp single phase machines to hook up. Thanks for the thorough answers so far.

240v 3ph motors operate at about 1/2 the fla as 240v 1ph motors. Check your motor plate on your 5hp 1ph and size the wire accordingly.