Breaker for Bridge Switch?

[dave777]

Starter circuits are a possible exception to the fuse/breaker rule.

But what about when the starter bank is bridged to the house bank?

Do you fuse / breaker the bridge?

I'm wondering if bridging is not a necessary or usefull option to begin with.
I'm wondering if an A,B, Both, Off switch can be modified to remove the Both setting.

[smac999]

the house line leaving the switch should be fused... if that is your question.


there is many different types of switches... the blue sea on / off / combine dual cct ones are now the most I use.

[dave777]

Originally Posted by smac999

the house line leaving the switch should be fused... if that is your question.


there is many different types of switches... the blue sea on / off / combine dual cct ones are now the most I use.

This is a starter circuit. The engine uses the starter batter on A, or the House bank on B, and OFF is an item. The switch also has "Both" which would in effect also function as a bridging circuit.

Perhaps this is not a good method to bridge banks, even though this common battery switch does so.

If the line to the house bank is fused/breakered, then when connected to house bank for starting the potential large rush of starting current is likely to blow the fuse/breaker. If to compentsate for this, the fuse/breaker is set too high, it defeats the safety purpose.

If no fuse is used, then when Both is selected, there is potentially a huge rush of current if one bank is too low, or shorted.

Should "Both" be disabled on the switch, or avoided except in extreme circumstances.

I could rig a dedicated bridge switch with a fuse/breaker. Is this the better approach? What value for this fuse/breaker?

[smac999]

like I said fuse the house panel feed line between the switch and panel... close to the switch.

[undercutter]

Originally Posted by dave777

Starter circuits are a possible exception to the fuse/breaker rule.

But what about when the starter bank is bridged to the house bank?

Do you fuse / breaker the bridge?

I'm wondering if bridging is not a necessary or usefull option to begin with.
I'm wondering if an A,B, Both, Off switch can be modified to remove the Both setting.

I always thought these types of switches were for 2 loads. eg main engine and generator start circuits but I can see how they could be wired as you indicate. Ours is with 2 loads and the parallel switch is a straight open closed contact switch which is not fused from the house bank.

If I were to install a fuse for this bridge I would think it would have to correspond directly to the amperage requirements of the starter motor. Your starter battery bank should also be sized for this amperage requirement and should give you some idea. We have an 1100 cca battery (8D) for our engine circuit. I would imagine that anything less than a 550 amp fuse wouldn't last long so I am not sure what good it would do.

Our bow thruster is potentially a 600 amp draw. It is protected by a 375 amp slow blow fuse. Yes we have blown this fuse.