Breakers overheating [RE-wrenches]

[Don Loweburg, Offline]

In a message dated 11/13/2000 10:47:36 AM Pacific Standard Time, 
wrmiller at slonet.org writes:

<<  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?
  >>


Bill I have several systems with 15 kw gensets with dual inverters. Have not 
had this problem. Since you subed this out- there may be something you don't 
know or your sub does not see. I would go on site and go over everthing. This 
is not a general problem.

One thing just popped to mind. If for some reason there were a large power 
factor this would result in large out of phase currents that might explain 
the heating and failure of the breakers. Again I suggest this will require 
your onsite attention.

Best, Don

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