40A SCC max wire size 8awg?

[rack04]

Good morning. Quick question. I'm looking at purchasing a Rover 40amp MPPT solar charge controller based on Will's recommendation. Based on my research this solar charge controller should be fused with a 50amp breaker and 6awg is acceptable for 50amps but the solar charge controller will only accept a max of 8awg. Do I fuse with 40amp and use 8awg instead?

 

[Just John]

I used 8 gauge wire (that's what fits) and a 50 amp breaker. I've never had 10 gauge wire get even warm at 40 amps, so I don't have a problem fusing 8 gauge at 50 amps.

 

[MichaelK]

The spec I see for the 40A Rover Elite is 6 gauge? Is that what you have?

 

[Just John]

I'm surprised, I didn't know Renogy had more than one 40 amp MPPT SCC.

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This is the one I assumed (you know what that means) you had. I have the Rich Solar version of the same.
8 gauge is what it takes (max). The other that @MichaelK found does accept 6 gauge.

Either version, a 50 amp breaker on 8 gauge wire is just fine.

 

[rmaddy]

You don't size the wire to the breaker. You size the wire to the load and then size the breaker to the wire. Good quality copper 8AWG can handle 40A just fine assuming you keep the length under 30 feet. But the shorter the better to minimize voltage drop (10 feet for 3% drop, even shorter is better). Even 10AWG can handle 40A if it's short enough but the voltage drop will be too high for a SCC. You can use a 50A breaker because that 8AWG wire will actually handle over 50A. You don't want a 40A breaker because you will likely get nuisance trips if you regularly try to push 40A through the wire.

 

[Just John]

You don't size the wire to the breaker. You size the wire to the load and then size the breaker to the wire. Good quality copper 8AWG can handle 40A just fine assuming you keep the length under 30 feet. But the shorter the better to minimize voltage drop (10 feet for 3% drop, even shorter is better). Even 10AWG can handle 40A if it's short enough but the voltage drop will be too high for a SCC. You can use a 50A breaker because that 8AWG wire will actually handle over 50A. You don't want a 40A breaker because you will likely get nuisance trips if you regularly try to push 40A through the wire.

Yes, I push 40 amps through 10 gauge wire for days on end when doing a top balance, but it is also about 3 feet. Doesn't get warm at all.