Just in from Square D [RE-wrenches]

[sunwise at cheqnet.net]

wrote:

> An ungrounded system will have a double pole breaker opening both the
> positive and the negative, which will do a much better job of
> suppressing arcs.
>
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?

Speaking of such, and in response to a recent post, I always thought
there was two ratings for over-curent protection.  The first, usually
covered by "regular" breakers was "currrent limiting".  The second, more
DC/T-fuse/battery related, was "current interrupting".  It's a different
deal disconecting a short circuit vs. interrupting a 20 amp flow with a
15 amp breaker.  This is especially true when all these DC
freaks/solar-boz's have adequatetly sized the conductors.  Is there a
de-rating for this?

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?

I like the idea of protecting QO's with "T's".  That said, I always
figured Hienkugles didn't need the added interruption protection.  I
thought that these were truely DC rated and could preforn both the
limiting AND interrupting functions.  Thoughts?

Kurt Nelson





Kurt Nelson

- - - - - - -
To send a message:
 RE-wrenches at topica.com

The archive of previous messages: 
 http://www.topica.com/lists/RE-wrenches/

List rules & etiquette:
 http://www.mrsharkey.com/wrenches/etiquete.htm

To unsubscribe send a message to: 
 RE-wrenches-unsubscribe at topica.com

To check out the other RE-Wrench participants:
 www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine: 
 www.homepower.com

For info contact list moderator by email:
 michael.welch at homepower.com

____________________________________________________________
T O P I C A  -- Learn More. Surf Less. 
Newsletters, Tips and Discussions on Topics You Choose.
http://www.topica.com/partner/tag01