Just in from Square D [RE-wrenches]

[Allan Sindelar, Positive Energy, Inc.]

If I cogitate (that's one a them five-dollar words like "paucity") on this,
it appears that we can't take advantage of the option of using 2-pole QO
breakers and load centers to allow higher-voltage DC operation, because of
the fundamental NEC requirement that one conductor (in our case the DC
negative) remain grounded. Unless I'm missing something, the circumstances
under which the 125 VDC rating is achieved don't work in the standard
"bond-the-negative-at-one-point-and-break-the-positive" approach that has
become the NEC-compliant standard, so the issue is moot.

I have never heard anything to suggest that breakers could not be sized
below conductor ampacity for DC. If it's true, we're in big trouble, because
sizing for voltage drop nearly always upsizes wire relative to sizing for
ampacity.

Can anyone elucidate (whups, jest slipped out)?

Allan @ Pos E
> Yup, I will admit that I am not well versed in this area of the code,
> but I do remember that at specific voltages, (low Voltage) DC systems
> could go ungrounded, but you had to provide current interrupt/disconnect
> (or was it current limiting?) on both the Pos and Neg.  Wonder if it
> would meet code to use a standard QO box, and bring the Pos in on one
> breaker leg and the Neg. in on the other breaker buss, then just use two
> poles?

> I once had a Square D guy tell me that a 15 amp QO breaker sould NOT be
> used on a circuit supplied with a 12 gauge wire.  He said it was just as
> bad as using a 20 amp breaker on a circuit supplied by a 14 gauge
> wire.   The large conductor changes a bunch of stuff that makes the
> breaker break when it should?   We're often lowing resistance as far as
> possible.  Cool?


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