Can a fuse be used to protect another fuse? (Class T Fuse Question)

[iClick]

I'd like to install a Class T fuse into my yet to be built 12v 310A power station. The reason for the choosing a Class T fuse is to protect against a catastrophic direct short where there could be in excess of 10k Amps (happy to be corrected here)

Now given that Class T fuses aren't cheap ($80 AUD) would it be feasible to install a higher rated Class T fuse than is needed by my cables and then properly rated ANL or MRBF fuses that I would hope would blow before the 'last resort' Class T fuse.

In my case, I have 64mm SQ 00B&S cable connecting a 2000W inverter to a 310Ah battery.

Would it be akin to wearing two condoms If I used a 250A ANL fuses to protect the cable and then have a 350A Class T fuse between the battery cut off switch acting as the direct short fail safe?

 

[LakeHouse]

For 12V systems, MRBF's have a 10k Amp interrupt current, I think.

But aside from that, I'm trying to come up with reasons why this is a bad idea but I'm coming up with nothing.

• Short? Protected by the Class T. Check.
• Overload (short or medium term)? Protected by the ANL (or MRBF). Check.

I'm happy to be corrected by others on this one, but this seems to be an ok plan?

 

[mikefitz]

there could be in excess of 10k Amps

With a 12v system and some resistance between the cells battery terminals, is unlikely to exceed 10k amps thus a MRBF 'master' fuse should be OK. If a ClassT or similar HRC fuse is used with a lower cost fuse downstream, this is OK provided the cable has a suitable current rating.

 

[iClick]

I'm happy to be corrected by others on this one, but this seems to be an ok plan?

this is OK provided the cable has a suitable current rating.

I appreciate your feedback and for the vote of confidence. I'm still pretty green at this but I want to make sure that everything is done with safety in mind.

I think I'll design the system to have a copper busbar from the battery terminal to the Class T fuse holder then battery disconnect switch followed by ANL fuses at the busbar.

 

[Brett V]

Put the Class-T as close as possible to the positive of your battery. I have Class-T fuses connected to the positive with about 12 inches of cable and then use 100 amp circuit breakers for the actual loads. See the pictures in my signature.