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diy solar

Circuit protection on SCC battery side?

MKB

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Joined
Dec 27, 2020
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I'm working on putting together my DIY solar energy station. I have all the major parts and the remaining cables are coming.

The one remaining question I have is circuit protection (fuse/breaker/etc) on the battery side of the SCC. In Will's designs (e.g., https://www.mobile-solarpower.com/the-classic-400-watt-rvs-vans-buses.html) he uses a circuit breaker or a fuse block on the positive line between the battery and SCC.

What is the purpose of the circuit protection here? Is it just to protect the wires in the event of massive over-current (e.g., short on the SCC side)? And does it matter what type? Do you need something fast acting (like an ANL fuse), or would a much cheaper MAXI or MIDI fuse or circuit breaker suffice?
 
The fuse is there to protect the wires from current from the battery. Consequently the fuse should be on the battery end of the wire going to the SCC.

The general consensus seems to be that there should be a 'main' class T fuse off the battery and then fuses on branch circuits after that. What is not yet clear is what the AIC (Amp Interrupt Capability) rating of the branch circuits need to be. Most folks seem to be using the lower AIC rated fuses for the branch circuits and best I can tell it is working for everyone..... but I have yet to see a good engineering explanation of how to calculate the AIC needed for the branch circuits.....

 
Thank you for the reply. I've got a MRBF terminal fuse (BlueSea 5185, 150A) that's intended to be the main battery OCPD. This is for a 12V (actually more like 14V since the battery is LifePo4) system with 1000W inverter so the current should normally be below 100A. The battery BMS says it can handle 200A for 30 seconds, but I don't intend to test that. Main battery wire is AWG 2 (oversized from the AWG 4 minimum according to the tables for 100A load).

For the SCC I think I will go for something simple to service (replace) and not worry so much about AIC. I am also thinking about sizing it "down" slightly. The SCC is rated for 50A max, but I might get a 50A fuse since I don't have enough solar to hit the 50A limit of the SCC currently. With an easy-to-replace fuse I could change that to 60A in the future if I buy more panels.
 
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