Battery fuse question

LeslieTroyer · Jan 11, 2019

If it’s within 7” of the battery technically no. I came off my house with two MRBF’s a 250 & 30. The 30 goes to a 24x7 fuse block for bilge pumps, vessel monitor...... the 250 went to a switch then a hot buss bar where I have 5 single MBRF’s for the items you describe plus the house CB panel. The hot buss bar can be switched to the start using the three switch as described my mainsail.

Les

dlochner · Jan 11, 2019

The fuse should be sized to protect the cable. The cable should be large enough to handle the maximum load. There are tables that give the values. If you are within 7 inches of the battery, it does not need to be fused, but the cable still needs to be large enough.

Maine Sail · Jan 11, 2019

Sefuller said:
I'd like to use a 3 position MRBF (Blue Sea 5194) with a common source direct from the battery. It will have fuses for the alternator, charger and ACR. Does the jumper to the MRBF block need to be fused, and if so, how do I determine the fuse size for this scenario?

The common source model 1 IN to 3 OUT is the 5196... The 5194 is 3 IN to 3 OUT.

I don't see you list a main fuse for the battery bank, just this charge bus, so yes, you would need an additional fuse before it. Over current protection is sized to protect the wire. So if you had a 2/0 105C jumper cable then a fuse of 300A would be fine. If this bank could ever be called up to start the motor the minimum fuse size should in 250A and up..

LeslieTroyer · Jan 13, 2019

Your boat your choice, but I like the security of fusing the battery.

Ron20324 · Jan 13, 2019

IIRC, the fuse should be within 7 inches of the battery to protect as much cable as possible.

LeslieTroyer · Jan 13, 2019

Ron20324 said:
IIRC, the fuse should be within 7 inches of the battery to protect as much cable as possible.

ABYC has exceptions for start battery. So manufacturers use that as an excuse not to spend the $$$.

Davidasailor26 · Jan 14, 2019

Sefuller said:
This brings up another question I am never sure of - when ABYC talks about protecting the cable does this eliminate the need for fusing at the battery, or merely extend the distance the fuse can be placed from the battery?

Protecting the cable means that the fuse should be between the power source and the cable, so that the current can't cause the cable to overheat. To protect the cable is exactly why you need the fuse at or near the battery.