30A receptacle with 20A circuit breaker

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You could put a 50 amp recept. on a 20 amp circuit. Min. wire size for the lugs in the recept. may be an issue however. Have no idea why you would want to either, but I'm sure it exists somewhere.
 
stickboy1375 said:
Its a good idea because no harm can come of it... :)
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As long as the breaker trips before the wire overheats. Apparently the NEC has a lot more faith in circuit breakers always working properly than I do.

So if it is safe for one receptacle, why wouldn't it be safe for 2 receptacles?
 
cpiper said:
I thought #12 copper MC would have a rating of 25A also, so someone explain to me why Southwire Armorlite Type MC cable only is rated 20A. See link.

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet66
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I don't have a code book near me at home right now, but somewhere in article 240 it states the maximum overcurrent protective device ratings for small wire. #14 has a max of 15A OCP, #12 has a max 20A OCP, and #10 has a max 30A OCP. If derating applies you can still start from the 90 deg C column in the tables and apply the temperature and bundling derating factors, but you still have those maximums for #14 thru #10 wire. Your first clue that some other ampacity limit applies is that in the tables in the link you posted, the ampacities are the same for the 60 deg, 75 deg, and 90 deg columns.
 
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Most centrifuges that require a 6-30R are 20 amps continuous load. Unless
it's a table-top I too would question it. I wouldn't worry about the breaker
I would be concerned with the conductors.
 
stickboy1375 said:
Why? The OCD protects the conductors, who cares what amperage rating the receptacle is? (as long as its a single receptacle)
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I'm not really concerend about the receptical. I'm concerned about the
equipment actually as I think about it. I know these machines quite well.
The NEC is a safety manual. I work in Labs everyday and I started thinking.
Lets say I designed this and I wired it per the NEC. Is it compliant yes,is it
safe yes. Now as a design it is terrible. Your a researcher in a lab and you
have deadlines to meet protocals to follow. You place your product in this
centrifudge for 5 hours at a predetermined RPM at a certain temp so that the
FDA will accept your test results. Now the breaker trips two hours in the
process, over and over again. Are the conductors protected,yes, Is this a
compliant install yes,does it function, no. I have to stop thinking
the bare minium safety compliance is all I have to meet in order to feel
I did a good job. This post has taught me that the NEC is important
to human , property safety,but propper design along with NEC compliance
is how things should be done. The NEC is not the be all end all. If it
were why would we need engineers or designers? Ok yes I'm on a
NEC forum, so let me have it, I'm old and can take it.:smile:
 
OK, so what do you guy's think about 210.23 (1st paragraph)? In my opinion, this is intended to prohibit a 30 amp receptacle on a 20 amp circuit.

I also think 210.23 (A)(1) also prohibits this.

Steve
 
steve66 said:
OK, so what do you guy's think about 210.23 (1st paragraph)? In my opinion, this is intended to prohibit a 30 amp receptacle on a 20 amp circuit.
I also think 210.23 (A)(1) also prohibits this.
Steve
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I don't see it that way.
210.21(B)(1) says "A single receptacle installed on a individual branch circuit shall have a amperage rating not less than that of the branch circuit"

That pretty much sums it up for a single receptacle on a individual circuit.

As far as 210.23(A)(1), you may be correct.
If that centrifuge has a current rating of more than 16A and is not fixed in place, it would require a #10 branch circuit.
I started to say that it would require a 30A circuit, but you could use a #10 wire and a 25A breaker.:smile:

Just my opinion
steve
 
steve66 said:
OK, so what do you guy's think about 210.23 (1st paragraph)? In my opinion, this is intended to prohibit a 30 amp receptacle on a 20 amp circuit.

I also think 210.23 (A)(1) also prohibits this.

Steve
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210.21(B)(1) is pretty explicit. As Hillbilly posted the wording spells it out rather clearly "not less than".

210.23 is for two or more receptacles not a single receptacle.
 
The last half of the paragraph is for 2 or more receptacles. But I was refering to the first half:

"In no case shall the load exceed the branch-circuit ampere rating. An individual branch circuit shall be permitted to supply any load for which it is rated."

To me, it also seems like 210.11, 210.20(A) and 220.18 all say you can't put a 30A receptacle on a 20A circuit.

Steve
 
steve66 said:
"In no case shall the load exceed the branch-circuit ampere rating. An individual branch circuit shall be permitted to supply any load for which it is rated."
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A receptacle is not a 'load'.


Think of it in larger terms, lets say I have a cord and plug piece of machinery that requires 65 amps non-continuous. The closest usable plug and receptacle to 65 amps would be 100 amps. Would you say I must supply that receptacle with 100 amp conductors and OCP?

IMO no I do not.
 
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