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Fuse size between battery bank and distribution panel


Adam1991

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Hi all, we’re planning our connections to the batteries from our dc positive control panel and negative bus bar on the boat.
 

We’re looking for some advice on a few elements: 
 

What size fuse should we have in line between the 400ah battery bank and the control panel? 200amp?
 

Where should this fuse be in the positive cable run should it be at the point where the cables connect to the batteries or nearer the dc control panel internally? 
 

Where should we ultimately connect up the dc cable feeding the bus bar and control panel? Should they be directly connected on to the batteries or connected on to the isolation switches in the engine bay? 
 

Thanks and sorry for so many question in one post ! 

Edited by Adam Mc Gowan
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1. Fuses protect the cable so what sized cable are you using?

 

2. Fuses should go as close to the source of electricity as practical but not in or adjacent to the batteries.

 

3. The master switch except the fees for any item the BSS allows to bypass the switch such as battery chargers and car radio memory fees. However, those supplies must also be fused.

Edited by Tony Brooks
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Hi Tony, thanks for your response. 
 

The battery cable will be 25mm sq. 

 

Am I right in thinking you only need a fuse on the positive run?

 

And from what you’ve mentioned above, a fuse in line on the first meter or so of leaving the batteries would be ok?

 

thanks! 

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3 hours ago, Adam Mc Gowan said:

Hi Tony, thanks for your response. 
 

The battery cable will be 25mm sq. 

 

Am I right in thinking you only need a fuse on the positive run?

 

And from what you’ve mentioned above, a fuse in line on the first meter or so of leaving the batteries would be ok?

 

thanks! 

 

Yes, only fuse the positive run.

 

12V Planet give 25 sq mm CCSA as rated at 170 amp so fuse at that or better still a tad less. However, that is for modern insulation (thin wall), older cable that you might pick up as a bargain may be rated at less than that.

 

As David says, as close to the battery box as practical. The longer the run between battery and fuse the greater the danger that the  unprotected length of cable might short out and catch fire.

 

Then fuse the individual circuits at the 12V distribution board, again at or below the cable's current rating.

 

If you have an inverter of more than a very few 100 Watts wire that on its own circuit with its own fuse.

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Thanks Tony, that’s very clear and helpful advice. We have an inverter already rigged up and now working on connecting up the distribution panel so this is very helpful. 
 

I’ve just ordered a 125amp fuse and holder so hopefully that does the job. 
 

thanks,

Adam 

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