L6-20P -> L6-30R

Lamar Owen lowen at pari.edu
Wed Mar 19 18:12:36 UTC 2014

[Whee.  This discussion is good for me, as I need to refresh my memory 
on the relevant code sections for some new data center 
clients.....thanks, Bill, you're a great help!]

On 03/19/2014 12:24 PM, William Herrin wrote:
> Yet an 18 awg PC power cable is perfectly safe when plugged in to a 
> 5-20R on a circuit with a 20 amp breaker. Get real man. 
The NFPA thinks so.  They also allow interoperability between a 20A 
T-slot receptacle and a 15A plug (so that a 2-15P can work in a T-slot 
2-20R, or a 5-15P can work in a 5-20R, etc).  Things are different above 
20A, at least in the NFPA's view.  NFPA 75 is interesting reading, 
especially in those sections where its committee and the NFPA 70 
committee seem to see things differently.

However, my SOP is to use no smaller than 16AWG for a 5-15P or 6-15P 
(with a 14AWG preference), and no smaller than 12AWG for 20A use, etc, 
unless protected by suitable overcurrent devices (for 18AWG, that's 7A, 
and for 16AWG that's 10A, so a power strip with a 10A breaker or a PDU 
with a individual 10A breakers is fine for use with 16AWG power cords).  
I do have an EE background and degree, and so I do tend to be very 
conservative in those things.  I have seen the results of pinched 18AWG 
zipcord in a 5-15R, and it's not pretty.

The 22AWG Christmas lights get away with it by having overcurrent 
protection in the plugs.

> You got two things right: The NEC (and related fire codes) don't apply 
> to supply cords of appliances in circumstances such as OP's PDU. The 
> modification cancels the UL certification. If you have an external 
> requirement to use only UL certified components then you can't make 
> any modifications no matter how obviously safe they are.By the way, 
> you either don't have that requirement or you're breaking it. Your 
> custom network cables are not UL certified.
Here's the bottom line, at least in my data centers:  if it could be 
considered questionable by the insurers (that's where UL got its start) 
then it's not likely to happen.  Modifying a piece of utilization 
equipment with a UL QPQY listing is likely to be considered questionable.

Now, network cable installation is covered by the NEC in article 800, 
which got some revisions in 2011, and the class 2 and class 3 cables 
used are also covered, in articles 725 (fiber is covered by article 770, 
and ITE rooms by article 645).  The major theme there is reduction in 
spread of products of combustion, and the UL DUZX listing reflects that 
purpose.  Yes, listed cables are required by code when part of the 
premises wiring, but putting a listed connector on listed cable is 
within the listing.

Further, 802.3af and even 802.3at are considered Class 2 power limited 
sources under article 725 of the NEC (that is, there's not enough 
available power to initiate combustion).

So, sure, I can still use custom network cabling and stay within using 
only listed items.

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