Hello everyone.

20 March was a bad day for me as we almost had a fire started in the house. I installed my solar setup about 3months ago. It worked fine until yesterday my wife started smelling plastic burning.

She rushed to the inverters and found smoke coming from the PV Combiner Box. Immediately she switched off everything until I got home from work.

After investigating, I found the Surge Protectors, plastic covers melted.

I rushed to town and bought a new Solar Wise Metal Case PV Combiner Box. Much steadier and really of decent quality.

I just can't imagine what would have happen if nobody was home.

Any suggestions why this could have happened?

First pic is the melted plastic box and the other 2 the new box.

Edited March 22, 20251 yr by Lourens1975
Changed topic

If the old box looked like the new box, I would guess that current was flowing through the connector between the surge arrestors. Do you have a photo before the fire?

What were the fuses rated for and what current flowed on the PV cable?

3 hours ago, Lourens1975 said:

Any suggestions why this could have happened?

Make sure all wire connection terminals are well tightened. Loose terminals with high current can heath up and the effect is worse with DC than with AC.

Also take in account that common circuit breakers are designed for AC. Their capability to break DC is limited to lower voltage. A not extinguished arc in a tripped breaker can put fire to the PV Combiner Box.

Good evening

I have double checked the new box for loose connections. Old box was definitely DC breakers, same with new one. 40A each. Unfortunately, no photos of old one.

Current was about 12.5A from each string and 325V.

Edited March 22, 20251 yr by Lourens1975

You can consider bypassing the SPD and fuses.

2 hours ago, Lourens1975 said:

Good evening

I have double checked the new box for loose connections. Old box was definitely DC breakers, same with new one. 40A each. Unfortunately, no photos of old one.

Current was about 12.5A from each string and 325V.

Only time I've seen this was when the fly by night sparky used AC breakers. As others have mentioned, loose connections could've also caused it.

DC arcs incredibly easily and heats up pretty quick. What I do to try prevent loose connections, is after a couple of days of the system running, I go back and check all connections again. I've seen it on both AC and DC sides before, where connections that were previously tight, are now extremely loose.

22 hours ago, Lourens1975 said:

Hello everyone.

20 March was a bad day for me as we almost had a fire started in the house. I installed my solar setup about 3months ago. It worked fine until yesterday my wife started smelling plastic burning.

She rushed to the inverters and found smoke coming from the PV Combiner Box. Immediately she switched off everything until I got home from work.

After investigating, I found the Surge Protectors, plastic covers melted.

I rushed to town and bought a new Solar Wise Metal Case PV Combiner Box. Much steadier and really of decent quality.

I just can't imagine what would have happen if nobody was home.

Any suggestions why this could have happened?

First pic is the melted plastic box and the other 2 the new box.

There will be speculation as to where the semi fire started and to the actual cause of the incident.

1. Arc occured due to loose connection or short cutcuit( possible)

2. What else????

   First of all combiner protection curcuit needs to be designed for solar array specific parameters. Combiner boxes off the shelve do not cater for this nor are the components used of best quality. It is all about keeping the cost as low as possible.

   Spd's are a critical component as it carries both pos and neg in one enclosure and therefore needs to be of good quality and EN 50539-11 certified. If the spd does not display this standard i will not use it.

   Furthermore what is the purpose of using a 40A curcuit breaker in a curcuit that as you mention is around 13A( Isc of string).

Below comparison between good quality spd( that has EN certification) and the non compliant counterpart.

Price comparison R~200 to Noark R ~800

Edited March 23, 20251 yr by TaliaB
Added pricing details on SPD's

11 hours ago, Bl4d3 said:

loose connections could've also caused it.

Here the physics behind the problem: Pure copper has the bad habit to flow away under pressure with time. Aluminium even worse. This effect is extreme with those terminals where the bolt directly squeezes the wire. There the surface pressure is extremely high. They require re-tightening after a while. The copper will have flown into positions where it can less flow away and presents a better surface to the bolt. Terminals with indirect clamping are much better as they present a larger surface to the wire. When ever I have to open the DB or inverters I re-tighten all terminals.

Hi Everyone

Thanks for all the good advise. It's been 4 days after I installed the new combiner box. Have been checking the temp with my thermal gun as wel. All wires and breakers ice cold and I've been running my whole house off the solar except for the gas stove.

I will wait a few more days and then re tighten everything again.

Be sure to scan the screws or bottom of the wire. This will show temperature rise more than the plastic breaker housing.

2 hours ago, Lourens1975 said:

I will wait a few more days and then re tighten everything again.

My advice is do a regular check not just after a short period. Due to the high current on the battery cables it is a quick check to do say every 3 months.

There is a lot of expansion and contraction that can cause loose connections.

As @frivan mentioned I have seen up to 80 deg C even on the PVC around the load terminals in the bottom portion on the DC MCB on a battery circuit. Terminals were tight.