Breakers overheating [RE-wrenches]

[Drake Chamberlin, Quicksilver Electrical]

I had a breaker mysteriously burn up on a generator circuit.  A 4.5 KW gen set
burned up a 60 amp breaker.  No satisfactory explanation ever surfaced.

William Miller wrote:

> Friends:
>
> I have a project I've sub-contracted and the sub-contractor is having a
> problem I can't explain.  The system is an off grid PV with 2 SW4024
> inverters and a 16kVA Onan backup.  The generator is new and is fed via a
> load center into the inverters.  Three circuit breakers in two load centers
> have burned up in this generator circuit.  The first was a 125 A GE load
> center with a 60 amp feeder into the inverters.  The second two breakers
> were 60 A Square D QO breakers in a 70 amp QO load center.  The inverters
> were set for 50 A on Line in 2 and the charging circuit at 30 A.
>
> I wasn't on site to witness this.  My only guess is that the 60 A breakers
> in a 70 A panel were too close to design limits to handle 50 A continuous?
> This does not seem possible considering the following:  Since the charger
> is set for 30 A, the client would need to draw 20 A on either leg for the
> inverter(s) to create a 50 A draw.  The battery charging circuit may draw
> 30 amps at first, but this should taper off relatively soon.  Therefore, it
> seems unlikely the system is ever drawing 50 A, at least not for any period
> of time.  Why then are circuit breakers burning up?
>
> I may suggest a 125 A panel.  Any other ideas?
>
> Thanks,
>
> William Miller
>
> __________________________________________________________________
> William Miller
> SLO Communications: Communications and Power Systems Consulting
> Chief Engineer, KCBX: NPR and PRI for San Luis Obispo and Santa Barbara
> PO Box 50, Santa Margarita, CA 93453
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> email: wrmiller at slonet.org
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For info contact list moderator by email:
 michael.welch at homepower.com

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