[RE-wrenches] Independent vs common trip breakers

[August Goers]

William,

Good points. Keep in mind that both of these breakers have handle ties
(both are two pole), it's just that one can trip independently and the
other forces both to trip. What is the correct solution for 240 V solar
inverters? It seems like common trip is the best way to go but I've not
been able to find any direct reference to this in a brief internet search.

 I'm a CA certified general electrician but the test didn't go into this
kind of detail.

-August

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of William
Miller
Sent: Tuesday, September 25, 2012 4:03 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Independent vs common trip breakers

August:

It's all about safety:  If one has a 230V circuit and you are incorrectly
using non-handle-tied breakers, when an overcurrent event occurs on only
one phase, only one breaker trips.  The circuit stops working but the
appliance is still energized with the other phase of AC.  A repair person
may inadvertently assume the circuit is off based on the non-operational
status of the appliance and, during repair, come in contact with
conductors or equipment energized by the breaker that is still on.

In a correct installation (handle-tied) an overcurrent on one phase
de-energizes both phases.

A similar scenario applies in situations with a "multi-wire branch
circuit," aka a shared neutral.  It is less likely that a dangerous
situation will occur because one circuit will still work.  Opening the
neutral can result in over-voltaging one circuit (been there, bought that
replacement cash register).  I am not a house electrician, but I think
dishwasher / garbage disposal multi-wire circuits require handle ties.
Anyone else want to clarify this point?

This is a subtle but important point.  This is an example of knowledge
that a non-licensed or under-experienced electrician may not posses, hence
the desirability of requiring meaningful licensure.

Sincerely,

William Miller



At 03:06 PM 9/25/2012, you wrote:
>Hi Wrenches,
>
>Do any of you know the reason why we might use an independent trip
>versus a common trip two pole breaker for a solar inverter? My
>understanding is that the independent trip will only trip the
>individual line effected by the overcurrent condition compared to the
>common trip which will trip both poles. Both are tied together by a
>handle tie and both lines must be flipped on at the same time. Cutler
>hammer is a good example of a company who makes both types.
>
>It seems like supply houses sell both types willy nilly.
>
>Best,
>
>August
>_______________________________________________
>List sponsored by Home Power magazine
>
>List Address: RE-wrenches at lists.re-wrenches.org
>
>Options & settings:
>http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
>List-Archive:
>http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
>List rules & etiquette:
>www.re-wrenches.org/etiquette.htm
>
>Check out participant bios:
>www.members.re-wrenches.org
>
>
>Internal Virus Database is out of date.
>Checked by AVG - www.avg.com
>Version: 8.5.455 / Virus Database: 271.1.1/5272 - Release Date:
>09/16/12
>18:34:00

Miller Solar
Voice :805-438-5600
email: william at millersolar.com
http://millersolar.com
License No. C-10-773985

_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive:
http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org