Author Topic: Combiner box arcing  (Read 718 times)

0 Members and 1 Guest are viewing this topic.

bigrockcandymountain

  • Newbie
  • *
  • Posts: 31
  • Country: ca
Combiner box arcing
« on: February 13, 2017, 07:27:20 PM »
Hello all,

Today I was working on my solar system adding some conduit and cleaning up the temporary install stuff and had just got everything back together and had the power back on to the combiner.  It made a decent arc out of the bus bar that ties the breakers together and tripped one breaker.  I was putting the plastic cover back on at the time so jostling the breakers around a bit.  I still don't think it should have done this.  I checked everything and all the screws were tight.  It also tripped the arc fault on the classic so it's nice to know that works. 

Any thoughts would be appreciated. 

The strings are wired 3 modules in series for about 110vdc open circuit

4 strings of 250w 3 off modules.  750w per string.

15a breakers. 

It likely had most of 15a and close to 60a on the bus side since it was full sun.   

I jostled it around intentionally a bit afterward and a different string showed some small arcing. 

I'm thinking the bus is too hard to make a good connection with the clamps on the breakers since they are designed for stranded wire. 




OperaHouse

  • Hero Member
  • *****
  • Posts: 1000
  • Country: us
Re: Combiner box arcing
« Reply #1 on: February 13, 2017, 08:43:50 PM »
Around 100V is not much to start an arc from a clearance issue.  A stray strand of wire that causes a short and evaporates will sustain an arc with a DC voltage of that magnitude.

joestue

  • Hero Member
  • *****
  • Posts: 1354
Re: Combiner box arcing
« Reply #2 on: February 13, 2017, 08:44:56 PM »
Did the breakers come with a torque spec for the terminals?

bigrockcandymountain

  • Newbie
  • *
  • Posts: 31
  • Country: ca
Re: Combiner box arcing
« Reply #3 on: February 14, 2017, 06:36:11 AM »
I'll check on the torque specs today.  They are midnite breakers and a midnite combiner box/bus bar so everything should be made to go together. 

It's a good reminder how happy DC is to sustain an arc. 

bigrockcandymountain

  • Newbie
  • *
  • Posts: 31
  • Country: ca
Re: Combiner box arcing
« Reply #4 on: February 14, 2017, 06:39:25 PM »
New moral to this story.  Don't put things together like this in a hurry. 

There were two breakers hooked up properly and two that the clamps were torqued correctly but with the finger of the combiner plate bus in the wrong spot so not in the clamp at all. 

These have been working fine for the last year.  I put it together in a rush when my generator quit and I needed the system up and running for construction.  All that was making the connection between the breaker and the bus was it sitting loose against the clamp. 

All is well now.  I went through the whole system and checked connections and torque. 


dbcollen

  • Sr. Member
  • ****
  • Posts: 353
Re: Combiner box arcing
« Reply #5 on: February 16, 2017, 08:33:50 AM »
That's why when I am assembling a combiner with a comb-bus I always assemble it out of the box and then snap all the assembled breakers onto the din rail as a single unit.