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Maximum wire size for DC Circuit Breaker in a PV Combiner Box


New Member
Oct 12, 2022
I'm finding it quite difficult to nail down wire size specification for DC Circuit Breakers. I'm most interested in the type we see in PV Combiner Boxes on Amazon as well as I've sent queries to several vendors. Anyone on here with hands on experience?

I'm running AWG 4 wire 50 feet x 2 from my charge controller to a future 12V PV panel install. All my gear is 12V and that is not going to change.

So can anyone tell me if AWG 4 wire will fit into a typical DC Circuit breaker? I've seen youtube videos where it was mentioned they were using AWG 4
wire but I'm having doubts.

This all affects which combiner box I use because, if I need to add a small bus bar to change wire size, the box will need the room.
Midnite makes breakers that can handle up to 2 gauge wire.
Midnite makes breakers that can handle up to 2 gauge wire.
Thank you.

I also just found out that WATTS247 use a Jiuce JCB3-63 which has in its .
Terminal size top/bottom for cable25mm2 / 18-4 AWG
I am using AWG 6 in my WATTS247 combiner. You can likely squeeze in AWG 4 but it will be a "fun" time.
Do you think the fuse size in the combiner box is ok? 15A? Or can you swap that out for 20A? I have a 4-2 from Watts247 but I wondered if I am only using half of the box, can I use 20A fuses for the two strings instead of the 15A? It stays under the 63A... I would take the other 2 15A fuses out and not use them. My strings should really have an 18A fuse by the math.

diy solar

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