Panels in Parallel and Protection

[Bala]

So like many I self installed off grid then joined the forum.

My understanding for a long time was that 3 panels in parallel and no protection between them could cause a problem if one panel went bad.

I had just not done anything about it for various excuses!

Today I got lucky as I was at home and outside. I know the smell of burning electrics.

Took me a little while to look up but I found where the smell was coming from.

So a lesson for all, once you know something needs to be done, dont put it off.

[Mike90250]

Dang ! Bummer about that, but glad it went no further.

[Bala]

It was good that I was home and the weather was fine. Not a lot of chance of house fire as its all steel, but if all the stars aligned it could have got very ugly.

As it is I have one other set of panels the same. I have disconnected one of the three for now.

[littleharbor]

What is the item near the bottom of the junction box with wire connected to it? It looks like a circuit breaker found in RV's. I had to replace one in my 5th wheel once. I've been in a lot of solar panel junction boxes and haven't seen something like this in them.

[Bala]

Yes its a circuit breaker. It was 11 years ago when I fitted them, I didn't remember they were in there. Not really doing anything but a connection point for the cables.

I realised, I have pulled the internals from the breaker and used the posts to terminate the cables of the three panels.

There is Neg connected to one side and Pos to the other.

[NorthRick]

Can someone explain why that is dangerous and the proper way to mitigate it?

[littleharbor]

Solar panels are current limited. They wont put out any more current than they are rated at. The components of a panel can withstand double the rated current. Once you get over the current output of 2 panels/strings in parallel you are in the danger zone. A short circuit in 3 or more panels/strings produces enough current to cause this kind of damage, or worse, thus any more than 2 panels/strings in parallel need to be individually fused. Remember a series string will only put out the current of the lowest amperage panel Thus all panels in series should have the same amperage rating.

[Wy_White_Wolf]

Can someone explain why that is dangerous and the proper way to mitigate it?

You mitigate it by putting a circuit breaker or fusible link in each panel circuit when you have 3 or more parallel panels.

WWW