30 amp plug on 20 amp device

[peter]

A question has come up on another forum. It seems this guy wants to run a band saw and a dust collector on one 220 volt circuit. In his own words: "A dust collector at 12A & a new band saw that is on the way. It will require 10A. Would it be ok to combine those into one 30A two pole breaker with the outlets in series, or am I pushing it?"
It has already been pointed out that he cannot install a 20 amp receptacle on a 30 amp circuit. The question is whether it is legal to attach a 30 amp plug on a 20 amp device?
410-56(i) seems halfway relevant with a reference to "current rating than that for which the device is intended" but the paragraph seems directed at recptacles and not plugs.
~Peter

 

[iwire]

Re: 30 amp plug on 20 amp device

No, neither of these devices if equipped with 15 or 20 amp plugs on them are designed to be protected with a 30 amp overcurrent device.

 

[hurk27]

Re: 30 amp plug on 20 amp device

Bob
If the motor for the band saw has a overload built into the motor that would protect the motor and the wire feeding it from over load and the same with the dust collector then the 30 amp breaker, receptacle and plug would only have to be protected for fault current wouldn't it? 430.52. I still think it would be a UL listing issue to cut off a manufacture installed cord end and install a different plug but I don't think the NEC address's this or does it?

 

[iwire]

Re: 30 amp plug on 20 amp device

Wayne I agree with you if these units are designed for hard wiring.

My answer is based on the units arriving as a UL listed units with 15 or 20 amp plugs on them.

If they have these plugs on them, IMO feeding them with a 30 amp OCP would be the same as ignoring the max OCP rating on a HVAC unit.

 

[pierre]

Re: 30 amp plug on 20 amp device

Try 210.21(B)(2) and (B)(3) ... 210.24 is a summary table of this.

Also take a look at the NEMA ratings of the various receptacles - you can find them online

Pierre

[ May 18, 2004, 09:29 PM: Message edited by: pierre ]

 

[websparky]

Re: 30 amp plug on 20 amp device

I don't think the appliance is equiped with the proper sized conductors for 30A.
Take a look at Table 400.5(A)

 

[apauling]

Re: 30 amp plug on 20 amp device

I think the best and safest way to accomplish this would be to run a 220/30 amp line(10-3 if romex) to small 4/8 panel and have seperate full size breakers for each 220/20 or 220/15 outlet.

paul

 

[stew]

Re: 30 amp plug on 20 amp device

I would like to use 30 amp plugs on 20 amp circuits also but 210.24 wont allow it. This im my case comes up in a boat storage yard. 90% of the boats with a shore power connection use 30 amp plugs. Athough the circuit supplying them is in a lot of cases 20 amps with a 20 amp breaker and the current in the circuit is never usually more than a heater at 8 amps and maybe a charger at 5 0r 6 it is still not code to change out the receptacle to allow the convenience plugging in the standard 30 amp plug. So we use a UL listed 20 to 30 amp adapter which is listed and approved for this application . Even tho we now have the same thing as if we changed out the receptacle we now meet code. I dont like this arraingement because we end up with another cord and plug connectio0n to loosen up in service and give trouble. The adapters with a 30 amp female and a 20 amp male are available at any good marine store.Perhaps this mite helpin your case.

 

[hurk27]

Re: 30 amp plug on 20 amp device

Now look at 430.32(C)&(D)

for a motor or motor-operated appliance that is attached to the branch circuit through an
(INSERT) attachment plug and receptacle, the overload device shall be an integral part of the motor or of the appliance. The rating of the (INSERT) attachment plug and receptacle shall determine the rating of the circuit to which the motor may be connected , as provided in Article 210.

I think this is a little vague and should have (manufacture installed) Where (INSERT) Is

By Pierre: Try 210.21(B)(2) and (B)(3) ... 210.24 is a summary table of this.

I don't find anything in these two articles that say this is a violation. All it is saying is if you have a 30 amp circuit any receptacle on it has to be rated 30 amps and total connected load of two or more devices can not exceed 24 amps or 80% of the circuit rating. which Peter has said would only total 22 amps.

As far as 400.5 table(A)Column B+ Yes if the cord is not a HS type then a #12 would only be allowed for 25 amps if it is HS then it allows for 30 amps.


Bob I was thinking that since these units are 220 volts almost all the ones I have seen are design to be hard wired and or can be converted to 120 volts by rewiring the motor. Just like air compressors that you buy for your garage. They even have the instruction's on rewiring them in the instruction book.

And if what Peter said:

Would it be ok to combine those into one 30A two pole breaker with the outlets in series

Wasn't just a typo and he meant parallel. Or did he mean that he was going to try to run two 120 volt tools in series on 240 volts?
as the band saw would have about 140 volts on it. until the blade got stuck in the work then the dust collector would most likely get the whole 240 volt minus the resistance of the band saw.

[ May 19, 2004, 01:24 AM: Message edited by: hurk27 ]

 

[peter]

Re: 30 amp plug on 20 amp device

Hurk,
That was a direct quotation. He said "series" but probably meant "parrallel".
~Peter

 

[hurk27]

Re: 30 amp plug on 20 amp device

Peter, I hope so

[ May 20, 2004, 01:16 AM: Message edited by: hurk27 ]

 

[bthielen]

Re: 30 amp plug on 20 amp device

It has already been pointed out that he cannot install a 20 amp receptacle on a 30 amp circuit. The question is whether it is legal to attach a 30 amp plug on a 20 amp device?

I'm curious, not strange, just curious. If it is not allowed to place a 20A recpt. on a 30A circuit why is it allowed to use 15A recpt on a 20A sm. appl. circuit? I believe it is okay to use a 20A recpt. on a 30A circuit since the supplied load would not exceed the circuit or the receptacle's rating. In a ground fault situation both receptacles would see current in excess of their respective ratings.

Obviously, one cannot use a 30A recpt. on a 20A circuit as the 30A load would exceed the circuit rating.

Please clarify. Am I missing something?

Bob

 

[websparky]

Re: 30 amp plug on 20 amp device

Hi Bob,

Please look at Table 210.21(B)(2).

 

[bthielen]

Re: 30 amp plug on 20 amp device

Tanx,

I blew right past that one.

Bob