30A receptacle with 20A circuit breaker

Status
Not open for further replies.
C

cpiper

Member
I observed an existing installation with 30A 208V receptacles with 3/12 MC cable spliced to #10 THHN wire that runs back to the panel that lands on a 20A/2P breaker. A centrifuge is plugged into the receptacle and the nameplate data lists its ampacity at 20A. While this doesn't seem like a good design, is it Code compliant? Is there anywhere in the Code that says you can't have a 20A circuit connected to a 30A receptacle? Also, I believe the 20A circuit breaker would need to be 100% rated. Opinions?
 
Because the receptacle is rated 30A, do you think #10's should be used back to the panel? I'm concerned that someone in the future will not realize that the 30A receptacle is limited by a 20A branch circuit.
 
cpiper said:
Because the receptacle is rated 30A, do you think #10's should be used back to the panel? I'm concerned that someone in the future will not realize that the 30A receptacle is limited by a 20A branch circuit.
Click to expand...


It's not required. What someone may or may not do there in the future isn't a concern of the NEC.
 
Well, the 3/12 MC cable is rated only 20A (per Southwire and Okonite). You could plug something into the 30A receptacle that exceeds the rating the wire. That would be hazardous, right?
 
I have to disagree. I don't think a 30 A receptacle is allowed on a 20 amp circuit per 210.21B2.

Steve
 
cpiper said:
Well, the 3/12 MC cable is rated only 20A (per Southwire and Okonite). You could plug something into the 30A receptacle that exceeds the rating the wire. That would be hazardous, right?
Click to expand...


12 AWG copper MC has a rating of 25 amps at 60 C or 75 C. But the fact is there is a 20 amp breaker protecting it.

As far as the future no one should be up sizing breakers without having investigated the circuit the breaker supplies. :smile:
 
Make that 210.21(B)(3). (B)(2) is for two or more circuits.

After all a 20A breaker will probably hold 30 amps for a long time.

Steve
 
Recepacles.

After looking at the OP again, I'm not sure I'm disagreeing.

I intended to say a 30 A receptacle would not be permitted on a 20A circuit.

But now I think Infinity was saying he doesn't see a problem with the existing 20A receptacle and the spliced #10 wire. That does sound OK.
 
steve66 said:
Recepacles.

After looking at the OP again, I'm not sure I'm disagreeing.

I intended to say a 30 A receptacle would not be permitted on a 20A circuit.

But now I think Infinity was saying he doesn't see a problem with the existing 20A receptacle and the spliced #10 wire. That does sound OK.
Click to expand...


A 30 amp single receptacle is permitted on a 20 amp circuit.
 
infinity said:
A 30 amp single receptacle is permitted on a 20 amp circuit.
Click to expand...


B3 also says for two or more receptacles, doesn't it.

Just when you think you understand something....

Doesn't sound like a good idea, but your right, the code does seem to permit it.

Steve
 
Status
Not open for further replies.
Top