Main fuse size?

[bigwow]

Just rewiring battery circuits after good advice from here, and fortune spent with Merlin. Forgot to ask about the size of the house bank main fuse, I didn’t have one before. The house bank is 340amp, so what size fuse would be in order?
Thanks
John

 

[VicS]

The house bank has a capacity of 340 ampere hours, is what you mean. That is simply a measure of how much electrical energy it can store ... like you measure the size of a water tank in gallons. It could probably deliver well in excess of 1000 amps, 2000 maybe, if shorted out!


Your fuse must be a size that is less than the safe current capacity of any otherwise unfused wiring that it supplies ... battery capacity is irrelevant.

In other words if a fault occurs the fuse must blow rather than any of the wiring heating up.

So to begin with then what is the size in mm² or AWG of the wiring from the battery to the control panel.

What also is the maximum current you are likely to draw at any one time. That is with all the lights on, the radar running, the microwave in use, the ice maker running, SWMBO using her hair dryer etc etc etc.

 

[bigwow]

The house bank has a capacity of 340ampere hours, is what you mean. That is merely a measure of how much electrical energy it can store ... like you measure the size of a water tank in gallons.


Your fuse must be a size that is less than the safe current capacity of any otherwise unfused wiring that it supplies ... battery size is irrelevant.

In other words if a fault occurs the fuse must blow rather than any of the wiring heating up.

So to begin with then what is the size in mm² or AWG of the wiring from the battery to the control panel

Oh dear nothing is easy with electrickery, I’ll have to go down to the boat and see if it’s on it. The panel came from Taplin already wired up several years ago, don’t suppose there is a usual size for a 20 breaker panel is there?

I was thinking about putting this fuse in the 35mm wire between the battery and the switch block I got from Merlin

 

[VicS]

The maximum safe current carrying capacity for 35mm² or 2 AWG cable would be best taken as about 95 amps. (Although with free air circulation around it, it could take double that)

The fuse should therefore be no greater than 95 amps.

However your maximum use is hopefully well below that and there is not a lot of point in exceeding that by more than a reasonable margin.

If you are buying from Merlin Powerstore one of the Maxi fuse holders and one of the maxi fuses would fit the bill except that it only takes 4 AWG max cable size! bu**er.

You may have to consder a "Mega" fuse holder and a 100 amp fuse but you may find a smaller fuse to fit elsewhere.

Sorry lunch is ready!

 

[bigwow]

Thanks for that info, I was thinking about the ANL fuse holder from the CPC catalogue and they do a 100A fuse to fit it, so this might fit the bill.
John

 

[VicS]

I did not manage to find it in the CPC catalogue but that sort of thing will be fine.

I did find Maplin do the same covered BEP Marine one that Merlin Powerstore do.

You should be able to fit smaller fuse than 100 amps. 80 and 50 are available. If 50 covers your needs then fit a 50.