Re: L6-20P -> L6-30R

[Lamar Owen <lowen () pari edu>]

On 03/18/2014 09:39 PM, William Herrin wrote:
> Meh. It depends. Plug that 30 amp power strip into a 20 amp circuit. 
> Try to use more than 20 amps and the main breaker trips. No problem. 
> Plug that 20 amp power strip into a 30 amp circuit. Try to use more 
> than 20 amps and the strip's breaker trips. No problem. Get a short 
> before the strip breaker and the main breaker trips before the wires 
> can heat. There just aren't a whole lot of failure modes here that 
> result in fire short of one or the other breaker failing. And that 
> results in fire regardless of the amperage mismatch.

The amount of misinformation in this thread is astonishing.

> This, by the way, is why you're allowed to plug that 22 gauge 
> Christmas light wire into a 15 amp receptacle even though it can't 
> handle 15 amps: the 3 amp fuse will blow if there's a short. Just 
> don't plug in anything with lower-rated wire that doesn't have its own 
> breaker or fuse. Regards, Bill Herrin 

Note that in those cases the fuse is in the plug; anywhere else wouldn't 
be ok.  As small as 18AWG may be used for fixture wire on a 20A circuit, 
per 240.5(B)(2)(1).

2011 NEC article 210.23(A) permits 15A receptacles on 20A branch 
circuits; 30A branch circuits must use 30A receptacles.  If the OP's 30A 
branch circuit has an L6-20R on it then this would be a violation; see 
NEC Table 210.24 for a summary of the code.

406.8 is the article requiring that cord caps (plugs) are not supposed 
to be interchangeable.

Now, article 240.5 is the relevant article in the NEC.  This can get a 
bit tricky to apply; if the PDU in question is *listed* for connection 
to a 30A circuit then that's OK (240.5(B)(1)); the individual fixture 
wires within the PDU for a 30A PDU can be as small as 14AWG as long as 
they're protected (240.5(B)(2)(4)), but field assembled extension cord 
sets for a 30A circuit would need 10AWG conductors, as they aren't 
covered by the exception in 240.5(B)(4) and thus fall under 240.5(A).  
It's definitely allowed to connect a 30A PDU with 10AWG conductors to a 
30A branch circuit; anything else could be OK, depending upon the local 
authority having jurisdiction and its interpretation of the 240.5 
exceptions, which aren't the clearest section of the NEC, IMO.  And 
article 645, dealing with ITE rooms, only requires that cords be listed 
for use with IT equipment and be less than 4.5m in length.

IMO, and my degree is in EE, it is possible to have a fault condition in 
a 12AWG cord that won't trip a 30A breaker but could cause a fire and be 
prior to the input breaker in the PDU.

The OP appears to be doing the right thing and getting a 30A PDU.