Failed breaker

[dapdan]

Midnite and all,

I would wish any input or theories for a failed breaker I just removed from a client setup. This is the set up

24v system with the following installed:

2000w pv
Xantres C60 cc
20A and 63A MNDC breakers
Mini disconnect Midnite panel
600Ah battery bank

System is not used at night(only up to about 8pm) as it is a business. Business operates from 10am to 8pm. Daytime loads can be high and sustained. Loads consume between 8-10kwh during operation. My client does alot of computer work during working hours so day time loads are high and constant. System has been runnig flawless for nearly two years(april 2012 installed date).

He called me on the weekend complaining that inverter was shutting down and one of the breakers was constantly tripping. I went yesterday and inspected it to find one of the breaker was scorched with the input clamp fused to the wire and some of the wire installation was burn off.

Any ideas what may have caused this guys. I had 3#20A, 1# 30A and 1#63A breaker installed in the MNDC disconnect book to handle array and controller to battery. The array breakers are fine it was the controller output breaker that seems to have failed. I will attach pictures of the installation.

Cheers...
Damani

[dapdan]

Here are some pics.

[dapdan]

Here are some more pics.

[Halfcrazy]

The green worries me that tells me there is moisture involved? It looks to me like the connection went high resistance (Maybe do to some corrosion) and then went into thermal run away?

[dapdan]

Ryan,

I am replacing the thnn building wire with some 4awg welding wire. I did look around to see if there were any signs of water leaks from the roof and there wasn't. The ceiling was painted white and it was clean without any signs of water leaks. I am unsure about the humidity, but there is quite enough ventilation with a 2ft square window and a 32" door that is always open once the business is operational. Wouldn't the mositure affect the other 4 breakers as well. The other breakers shows no sign of moisture as I had removed one of them and inspected the input and output wires.

Cheers...
Damani

[TomW]

Maybe it is pre install contamination of the cable in storage?

I find that I never have corrosion problems (inside or out) when I use No-Ox grease on the connections. I would suggest a tube of it and liberal use to prevent this. Seems to be good insurance for a bit of time and very little cost. It allows dissimilar metals to be used together like aluminum to copper, also.

Just a thought.

Tom

[dapdan]

Tom,

Thanks. I have some battery terminal protector and I will use some on the new wire install. Be aware that this same wire was installed for nearly two years. It is a good idea to use some protective coating it can't hurt.

Cheers...
Damani

[Halfcrazy]

Yes I agree the fact it is that single wire is kind of odd. But the green does show it has at one time been exposed to moisture. It could very well be pre install as Tom pointed out and caused just enough tarnish to make it high resistance

Ryan

[dbcollen]

The corrosion is likely from the burnt PVC insulation. When PVC burns it liberates Chlorine, which is corrosive to copper.

[zoneblue]

Those breakers are extremely reliable and as others have said this looks like a classic case of screw retorque required after comissioning. Its easy to forget , done it myself. Copper is maleable and just loosens after some time especially at the beginning.