Battery isolation switch.

[Uncle Bob]

Hi, I have decided to install isolation switches on my multiple battery house bank. Each battery has a 100 amp fuse, the question is should the switch go between the battery and fuse or between the fuse and the positive bus bar?
Cheers, Bob.

[sailormed]

The fuse is there to protect the battery from overcurrent. So if anything goes wrong inside the isolation switch the battery still needs to be protected.
So fuse between battery and switch.

[two-rocks]

Fuses protect the wire, not the battery.
The fuse rating is based on the wire cross sectional area.
Different countries have different guidelines as to where or how close to the battery, or even how much you can exceed the wire rating to handle inrush.

[Frankly]

Fuses are included to protect all the components of the electrical system (including the battery(s)). As close to the battery terminals as practical is usually best.


Frankly

[smac999]

Originally Posted by sailormed

The fuse is there to protect the battery from overcurrent. So if anything goes wrong inside the isolation switch the battery still needs to be protected.
So fuse between battery and switch.

Please explain how a switch wound fail in any way that would requiring fusing.


You can do it either way. Having the switch first makes it safer to replace the fuse.

If you can use mrbf fuses it makes it really easy to install though and then the fuse goes first.

Keep in mind cable length rules to fuses.

[YANDINA]

The switch and fuse can be in any order. Having the switch first would allow you to change a fuse without any voltage or current involved which is important for high voltage systems but not significant on low voltage battery systems.

WARNING:
When using a Trollbridge 24, either both positive leads or neither positive lead should be fused, never just one. The problem with a single fuse is the batteries are connected in parallel by the Trollbridge 24 when idle and if the fuse on the starting side blows there is no fuse to limit current from the second battery. Now when you go to start the motor, the heavy starting current has to flow from the un-fused battery, through the Trollbridge and to the starter motor. This will blow the internal safety fuse in the Trollbridge or smoke the insulation on the cables depending on how much current is flowing.