[RE-wrenches] DC circuit breakers in parallel

[Exeltech]

William and all,

Our larger UL-certified inverter systems at Exeltech are routinely
built with multiple individual breakers with the handles pinned
together to create a higher-amperage device.  To William's point,
and by way of example, it's common for us to have three 100-amp
breakers ganged together with hardware designed for that purpose
(typically a knurled pin and an outer sleeve) to create [in effect]
a 300 amp breaker.

It takes special hardware to ensure absolutely free movement of
the breaker handles and avoid interference with the mechanical
aspects during a "trip" action that may otherwise prevent the
breaker from opening properly during an actual over-current
event.

While there are *some* breakers that are internally ganged, all
such units I've ever seen have a double-wide body, but just one
handle.  If there are breakers with more than two that are thus
internally ganged .. I've not seen them. (Not saying they don't
exist, just that I personally haven't seen any.)

For the past 12 years, I've been in charge of the UL program at
Exeltech.  As long as the breakers we use are NRTL "Recognized",
with ratings that are appropriate for the circuit voltage and
current, our equipment is accepted and certified by UL (and the
other NRTLs).  This includes breaker "stacks" we essentially
create from individual breakers in parallel.  We have literally
hundreds of models of inverters built this way, all UL Listed.

As a point of personal comment, anyone ganging multiple breakers
together in this manner should also utilize the connection concept
commonly used for multiple parallel batteries -- make connections
at the opposite diagonal corners to help ensure equal current flow
in all of the breakers.

Also ...for anyone not familiar with "NRTL", it means "Nationally
Recognized Testing Laboratory", such as UL, Intertek, CSA, etc..


Larry's application was mobile, so in the end, the NEC didn't
apply in his situation, but I credit him for asking as part of
his due-diligence to help ensure best practices were employed
in his project.

This has been a very interesting thread where the NEC *would* be
a consideration.


Regards to all,



Dan Lepinski
Senior Engineer
(41 years in the RE industry and it's still fun)


--- On Wed, 2/27/13, William Miller <william at millersolar.com> wrote:

> From: William Miller <william at millersolar.com>
> Subject: Re: [RE-wrenches] DC circuit breakers in parallel
> To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
> Date: Wednesday, February 27, 2013, 11:56 PM
> Larry:
> 
> I was tempted to advise against this.  I see a similar
> concept with people trying to parallel PV feeds and then
> putting two charge controllers at the destination.  Not
> good.
> 
> However, I see many 200 amp main breakers that are 4
> 100 amp breakers ganged, with two for each phase.  I
> can not presume to know about the requirements of
> internal ganging.
> 
> William Miller
> 
> 
> 
> > At 08:06 AM 2/27/2013, you wrote:
> > Hello Wrenches,
> >
> > I am installing a Classic 150 controller in an RV with
> > potential 95 amps output at 12 volts. The customer has a
> > Midnite DIN box and wants me to use it for the controller
> > output. I am out of 150VDC breakers but I have two 60 amp
> > breakers. Is it safe and reliable to use the 2 breakers in
> > parallel for this purpose? I can pin the two handles together.
> > There will be other circuit protection at the battery.
> >
> >Thank you,
> >
> >Larry Crutcher
> >Starlight Solar Power Systems