Breakers overheating [RE-wrenches]

William Miller wrmiller at slonet.org
Mon Nov 13 10:47:00 PST 2000


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
Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
email: wrmiller at slonet.org
License No. C-10-773985
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