How do I stay safe installing my solar if I didnt buy a battery cutoff, or isolator/breakers and general safety advice for installing/uninstalling?

[Gueyog8a7]

Yes, since the battery supports up to 100A continuous, need at least 125A fuse to support that. 150A fuse is fine.
Make sure your wire have ampacity 150A.

The branch circuits are protected to 40A with their own fuses.

Well the wire is 170a as discussed in OP.

 

[Hedges]

Vendor called it 170A? What gauge or cross section? What insulation temperature rating, or type?
If a vendor rates wire based on current not technical specifications, that may be assuming intermittent use.

 

[mikefitz]

Where should they go? Right after the mrbf on the battery end?

As near as practical, the distance won't matter too much if you are using 170 amp cable, as the MRBF fuse protects this cable.

so the mrbf fuse at 150a is fine

You may as well use it if you have purchaced a 150 amp fuse. It's intended to deal with unusally high fault currents, so since you are using 170 amp cable, a fuse 100 to 150 amps is OK. With your modest requirements and limited charging the typical maximum current will be a few 10s of amps. Sorry about the conflicting advice. The battery BMS limit at 100 amps is a factor. Mostly when calculating fuses you estimate the maximum current flow and use a fuse 125 to 150 % higher.

make use of the fuse holders I had already bought rather than buying midi fuses and holderscable is 25mm2

Yes no problem. Only advised midi since they are easily available 30 amps to 150 amps.

Well the wire is 170a

Comments on the cable. I guess it's automotive cable from 12v Planet. ( UK supplier), cable 25 mm2 rated to 70 degC , manufacturer AMC. This 170 amp is the maximum, at higher ambient temperatures or in looms/ conduite you de rate the cable. In your application there is no worry as it only has to carry fault current until the 150 MRBF , mounted on the battery post, protects. With the very small cable run between the MRBF and the 40 amp link fuses the risk of over rating the cable is almost non existant.

Mike

 

[Gueyog8a7]

As near as practical, the distance won't matter too much if you are using 170 amp cable, as the MRBF fuse protects this cable.

You may as well use it if you have purchaced a 150 amp fuse. It's intended to deal with unusally high fault currents, so since you are using 170 amp cable, a fuse 100 to 150 amps is OK. With your modest requirements and limited charging the typical maximum current will be a few 10s of amps. Sorry about the conflicting advice. The battery BMS limit at 100 amps is a factor. Mostly when calculating fuses you estimate the maximum current flow and use a fuse 125 to 150 % higher.

Yes no problem. Only advised midi since they are easily available 30 amps to 150 amps.

Comments on the cable. I guess it's automotive cable from 12v Planet. ( UK supplier), cable 25 mm2 rated to 70 degC , manufacturer AMC. This 170 amp is the maximum, at higher ambient temperatures or in looms/ conduite you de rate the cable. In your application there is no worry as it only has to carry fault current until the 150 MRBF , mounted on the battery post, protects. With the very small cable run between the MRBF and the 40 amp link fuses the risk of over rating the cable is almost non existant.

Mike

Ok. I was also thinking that since I have bought the 40a fuses for the individual wires off the main terminal the 100a or 150a is redundant isnt it since it will only be acting as short circuit protection and the lower 40a fuses will act as protection in the other instances discusses? Is that right?

 

[Hedges]

Ok. I was also thinking that since I have bought the 40a fuses for the individual wires off the main terminal the 100a or 150a is redundant isnt it since it will only be acting as short circuit protection and the lower 40a fuses will act as protection in the other instances discusses? Is that right?

I bought an mrbf fuse of 150a based on this advice.

Yesterday I bought a variety pack of fuses, and got 2x megafuses rated at 40a.

The 150A fuse is the only protection for shorts before where the 40A fuses are located.

MRBF has 2.5x the AIC rating of Mega.

If there is a dead short after the 40A fuse, 40A fuse might pull an arc, given the fault current available from lithium battery, and not protect against wires starting a fire. MRBF would then blow, interrupting the arc. That's not "redundant."

It is good if there are covers over the fuses. The Mega could blast its contents during failure.
Ideally there would be coordination of time to blow, so for such a fault, the higher AIC rated fuse blows faster, before the lower rated fuse creates and arc-blast. That sort of design and ratings is a thing in bigger installations, for instance safety switches able to carry fault currents long enough for upstream OCP to clear.

This isn't entirely being pedantic when dealing with little battery systems. One guy here managed to blast a link between lithium cells without blowing his class-T fuse (link apparently poorly connected.) So having things covered is good.