On 03/19/2014 09:51 AM, William Herrin wrote:
Nobody is talking about putting an L6-20R on a 30 amp circuit. OP was talking about putting an L6-30P on a 20 amp appliance: a PDU that has its own 20 amp breaker. Big difference.
If the PDU isn't listed for 30A then it's the essentially the same thing, safety-wise. Unless there is overcurrent protection at the source of the feed to the conductors of the flexible cord (240.21) that meets the ampacity of the conductors of said flexible cord, unless one of the exceptions of 240.5 apply, then it's a potentially unsafe condition (NEC doesn't directly apply to supply cords of appliances themselves; that's what the 'listing' is for from UL or similar; see http://ecmweb.com/code-basics/nec-rules-overcurrent-protection-equipment-and... for more info, and see UL's FAQ entry for modifications to listed equipment at www.ul.com/global/eng/pages/offerings/perspectives/regulator/faq/). Just replacing an L6-20P with an L6-30P on a 20A-listed PDU would be unsafe and (IMO) unwise, since the breaker in the input of the PDU does not protect the flexible cord's conductors from internal overcurrent faults. A 20A listed PDU should have 20A overcurrent protection to the connected receptacle, in addition to any overcurrent protection internal to the PDU. A cord with a 20A ampacity may overheat significantly if it faults internally in such a way as to cause more than 20A, but less than 30A (or whatever overcurrent protection is in the branch circuit), to flow; there are numerous ways cords can fault in this manner. You could easily get a situation where the cord is partially faulted internally but the PDU's breaker doesn't detect it because the fault shunts current ahead of that breaker; again, not a dead short but still an overcurrent fault. I've seen this type of fault before, where the cord itself was shunting a few amps prior to the PDU input breaker (in this particular case the cord was damaged by lightning, even though the equipment to which it was connected still had power). But the other condition, where a 20A breaker is feeding a 30A PDU, could result in dropping power to the PDU but is not unsafe. I know that I wouldn't approve (in the NEC-speak sense of that word) of the use of any of these adapters or similar kludges in my data centers, as the insurance liability issues are potentially much more costly than just buying the right PDU or running a branch circuit with the correct overcurrent protection in the first place. It also depends a bit on exactly how the PDU is listed. You can look up the listing's details in the UL White Book (download link: http://www.ul.com/global/documents/offerings/perspectives/regulators/2013_WB... ). But the final say rests with the authority having jurisdiction, AHJ in NEC-speak.