Simple (I Hope) 240V AC Electrical Code Question

[Chris Friesen]

Obviously with a plug and outlet you have two additional sub-breaker components to worry about; and there is the chance you will just forget about it and plug a welder in there. I tried a 30 amp breaker and found it worked just fine. Grizzly's recommended 40a was unnecessary; so I didn't have to make a choice.

Actually, a welder will likely have its own overcurrent protection (and is covered under 430) and so will be fine. The danger is plugging in something like an electric heater that is developing a problem and drawing more current than it's rated to handle. In that case the heater would be relying on the breaker for overcurrent protection, but the breaker would be sized to provide only electrical short protection.

[Julie Moriarty]

I am an electrician. I've wired everything from houses to 60 story office buildings, from fan motors to 2000 HP cooling towers, from toy stores to particle accelerators. And I've done a lot of electrical design work for construction ready drawings that have been built and passed inspection countless times. This is a pretty easy problem.

You have a machine with a NEMA 6-20P cord end and a NEMA 6-30R receptacle. Change your NEMA 6-30R receptacle to a NEMA 6-20R receptacle and enjoy your machine.

Yes Andy, it's a simple question and that has a simple solution.

[Rick Christopherson]

You have a machine with a NEMA 6-20P cord end and a NEMA 6-30R receptacle. Change your NEMA 6-30R receptacle to a NEMA 6-20R receptacle and enjoy your machine.

Yes Andy, it's a simple question and that has a simple solution.

No Julie, it is not that simple. You cannot put a 20-amp receptacle on a 30-amp circuit. And for 30-amp circuits, it doesn't matter whether it is a single receptacle or multiple receptacles. This is covered in the NEC quotes below:

Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or where larger than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.

Receptacle Ratings for Various Size Circuits

Circuit Rating (Amperes)	Receptacle Rating (Amperes)
15	Not over 15
20	15 or 20
30	30
40	40 or 50
50	50

[Julie Moriarty]

Rick, we're not talking about that receptacle being used as a general power source by who-knows-who for whatever purpose. It's going to operate a single machine in the OP's house. In this particular situation, there is nothing wrong or unsafe with just changing out the receptacle. No need to make the OP jump through hoops or do work he may not know how to do safely just to satisfy a code that is designed to cover a multitude of situations.

[Rick Christopherson]

Julie, if you look at my first posting in this thread, I indicated that if the OP and I were chatting over the backyard fence, my advise to him would be different than what I can present here. I wouldn't hesitate to do something like this in my own shop, but I am not a typical home owner.

But more importantly, the OP specifically asked what was code compliant. In that regard he is limited to reducing the breaker to 20 amps with a new receptacle, or replacing the cord cap on the tool. Which of those two options is best depends on how much he is willing to spend. I have an opinion on how I would proceed, but I have deliberately refrained from giving it here in this thread.

Question: Can I remove the 6-30R receptacle and replace it with a 6-20R receptacle and still have the circuit be code compliant, or must I remove the molded in plug and replace it with a 6-30 plug? My preference is to leave the cord alone.

Edit: P.S.: I have looked through article 430, specifically 430.42(C), and you still cannot put a 20-amp receptacle on a 30-amp circuit even under article 430.

[Rollie Meyers]

Julie, if you look at my first posting in this thread, I indicated that if the OP and I were chatting over the backyard fence, my advise to him would be different than what I can present here. I wouldn't hesitate to do something like this in my own shop, but I am not a typical home owner.

But more importantly, the OP specifically asked what was code compliant. In that regard he is limited to reducing the breaker to 20 amps with a new receptacle, or replacing the cord cap on the tool. Which of those two options is best depends on how much he is willing to spend. I have an opinion on how I would proceed, but I have deliberately refrained from giving it here in this thread.



Edit: P.S.: I have looked through article 430, specifically 430.42(C), and you still cannot put a 20-amp receptacle on a 30-amp circuit even under article 430.

I agree, plus NEC table.210.24 would limit a 20A receptacle to 20A overcurrent protection.

[Jim Neeley]

Edit: P.S.: I have looked through article 430, specifically 430.42(C), and you still cannot put a 20-amp receptacle on a 30-amp circuit even under article 430.

Rick,

Sec 430.42 is entitled "Motors on General-Purpose Branch Circuits" and 430.42(c) refers to "Cord and Plug Connected - Motors on General-Purpose Branch Circuits".

If this is set up as a general purpose branch circuit, I would agree. If it is set up to be dedicated to this motor service, that does not apply.

+1, Julie.

That said, I do understand the concern others have stated that some future owner of the home may consider it a GP circuit. This is the reason why I have labeled the receptacle and intend to swap the breaker before I sell the house. I figure the label will catch the eye of an inspector, should something happen to me prior to its sale. Nevertheless, it is not expressly stated in code that this must be done.

Additionally, being a one man "shop" and not in a public place, the probability of my wife (who is aware of this) or my dog (the other resident of the home) plugging a 240V 20A device into that receptacle is... Let's just say it's less than my getting run over by a bus on the way home tonight.

Jim

[Rick Christopherson]

Rick,

Sec 430.42 is entitled "Motors on General-Purpose Branch Circuits" and 430.42(c) refers to "Cord and Plug Connected - Motors on General-Purpose Branch Circuits".

If this is set up as a general purpose branch circuit, I would agree. If it is set up to be dedicated to this motor service, that does not apply.

Jim, I wasn't claiming 430.42 applied. I brought it up as an aside because previously in this thread people were claiming section 430 was an exception to 210.21.

As you just pointed out, 430.42(C) does not apply, and therefore, it cannot be an exception to 210.21. So unless you can find an applicable exception to 210.21, then 210.21(B) is binding and you cannot put a 20-amp receptacle on a 30-amp circuit.

The OP didn't ask how you would do it or I would do it, or anyone else would do it. He asked how it can be done while still being code compliant.

[Julie Moriarty]

If adhering to the code is of primary concern, the first thing I advise is to call the inspector. If you don't want to involve the inspector, know the municipal code. Many municipalities amend the NEC and some have completely rewritten it. Walk into those places and start reciting the NEC and you'll be laughed out of the building. In my career I found it a rarity when a municipality followed the NEC verbatim.

If there will be an inspection and there's even the slightest doubt about interpretation, call the inspector first. It never ceased to amaze me the ways some inspectors interpreted their code. Some even made up on the fly. I could write a book.

If fire safety is your primary concern, call the fire inspector. His or her word usually overrides that of the building inspector anyway.

In this kind of case you have another factor that I think would of major concern to anyone purchasing a brand new machine - manufacturer's warranty. Whenever I was asked to alter the electrical components of a new product, I would first warn the owner about possibly voiding the warranty. I've done installations where I had to hard-wire the machine in to meet code or the requirements of the customer. All were notified about warranty issues before I began the work. I never even changed an unmolded cord end, that could be easily changed back, without discussing warranty issues with the owner.

What makes no sense to me here is why Laguna would provide a 20A-rated cord end and then require the protecting breaker to be 30A. I've done installations where the manufacturer requires conductors to be rated higher than the breaker, that's not unusual. In those cases the concern was usually voltage drop because in industrial or commercial applications the installing contractor sometimes tends to push the limits or simply ignores voltage drop issues and many electrically powered products don't like lowered voltages feeding them. The tend to have a shorter life.

Andy, If you call Laguna and you're lucky enough to speak to the person who wrote the instructions, I'd love to hear the logic behind requiring a breaker over twice the amperage of the motor's FLA. I doubt the start-up load spikes that high. But maybe there was some concern about voltage drop or maybe it was just an error that hasn't been caught. Whatever the case, my concern would be making sure whatever you do wouldn't void the warranty.

[Phil Thien]

What makes no sense to me here is why Laguna would provide a 20A-rated cord end and then require the protecting breaker to be 30A.

My best guess is that part of the manual is a cut and paste from another machine manual that does need 30A.

Or it is entirely possible that, as someone pointed out above, the slow startup of the cast iron *may* trip a breaker, and they just don't want the calls about it.

But I've been amazed at the amount of cutting and pasting that goes on in manuals for computer gear.

[Wade Lippman]

Andy, If you call Laguna and you're lucky enough to speak to the person who wrote the instructions, I'd love to hear the logic behind requiring a breaker over twice the amperage of the motor's FLA. I doubt the start-up load spikes that high. But maybe there was some concern about voltage drop or maybe it was just an error that hasn't been caught. Whatever the case, my concern would be making sure whatever you do wouldn't void the warranty.

Not all breakers are created equal. I had two 20a circuits; one for my cyclone and one for tools. The cyclone kept tripping the breaker, despite the fact it was well under the trip curve. I swapped breakers and all was well.
Somebody installed it with 20a breaker, as common sense dictates. He kept tripping the breaker and calling up Laguna and screaming at them about their lousy equipment. Laguna figured they could avoid problems like that by specifying a 30a breaker. I will give you 10-1 odds it was something very similar to that.

[Steve Milito]

The warranty issues for replacing the power cord or the plug are essentially nonexistent if you do it correctly. The only possible reason they would not honor the warranty is if you damage the motor by wiring it incorrectly and ask them to replace it under the warranty.

[Chris Friesen]

As you just pointed out, 430.42(C) does not apply, and therefore, it cannot be an exception to 210.21. So unless you can find an applicable exception to 210.21, then 210.21(B) is binding and you cannot put a 20-amp receptacle on a 30-amp circuit.

I think the missing piece of the puzzle is that it's not actually a 30-amp circuit. The conductors (and hence receptacle) are sized based on the motor, then the breaker is sized separately.

In this case it's actually a 20-amp circuit (so the 20-amp receptacle is allowed) but under 430.52(C)(1) the breaker could conceivably be up to ~70A.

If you think about it, this makes sense. The overcurrent protection on the motor will prevent long-term overcurrent. The breaker will protect against short circuits. The 20-amp receptacle can certainly handle far more than the rated value for short amounts of time without overheating.

That said, to reduce confusion (witness the length of this thread) it's simplest to just treat it as a general purpose circuit.

[Wade Lippman]

I think the missing piece of the puzzle is that it's not actually a 30-amp circuit. The conductors (and hence receptacle) are sized based on the motor, then the breaker is sized separately.

So you are saying that with the motor plugged in it is not a 30a circuit and is code compliant with a 20a outlet, but when you unplug the motor it becomes a 30a circuit and doesn't meet code because the motor is no longer taken into account? (I realize you didn't actually say the second part, but it has to follow)
I can't see an inspector allowing that.

Hopefully he has cut the plug off by now, as I suggested 66 posts ago.

[Rick Christopherson]

So you are saying that with the motor plugged in it is not a 30a circuit and is code compliant with a 20a outlet, but when you unplug the motor it becomes a 30a circuit and doesn't meet code because the motor is no longer taken into account? (I realize you didn't actually say the second part, but it has to follow)

I would have said the same thing, but you worded it better than me.