Battery cable size?

[VicS]

I have gone with 25mm, reason being it is the minimum on the BSS, i should of checked there first, but i still had to know the question. With 25mm and 10 amp draw, VD is 0.25% so well in with 3% max.


Thanks all for the help, as always appreciated

As pvb implies master switch to domestic panel is not on that list but while you are using 25mm for the high current items that are you might as well use it for that too. Hopefully it will fit the terminals.

You dont say what engine you have. You might need heavier than 25mmm for that

 

[pvb]

You dont say what engine you have. You might need heavier than 25mmm for that

I doubt it, he has an outboard (see post 6).

 

[VicS]

I doubt it, he has an outboard (see post 6).

Ta. Missed that. Own battery too!

 

[waynes world]

That's only for high-current cables, eg starter, bow thruster, windlass, inverter.

As pvb implies master switch to domestic panel is not on that list but while you are using 25mm for the high current items that are you might as well use it for that too. Hopefully it will fit the terminals.

You dont say what engine you have. You might need heavier than 25mmm for that

Just to check, i can use the 25mm from batteries to master switch then from master switch to the fuse/consumer boards 6mm or even 3mm as these are very short, .5m and VD is less than 1% with the 3mm so less than half for 6mm cable.

Am i working this wrong as i put in 20amp draw ( .33% VD ) which is more than double what will be drawn when all fittings and on.

 

[pvb]

Just to check, i can use the 25mm from batteries to master switch then from master switch to the fuse/consumer boards 6mm or even 3mm as these are very short, .5m and VD is less than 1% with the 3mm so less than half for 6mm cable.

Yes, you can do that. But remember to put a fuse close to the battery.

 

[VicS]

Just to check, i can use the 25mm from batteries to master switch then from master switch to the fuse/consumer boards 6mm or even 3mm as these are very short, .5m and VD is less than 1% with the 3mm so less than half for 6mm cable.

Am i working this wrong as i put in 20amp draw ( .33% VD ) which is more than double what will be drawn when all fittings and on.

As pvb says you can do that but I would use the same size for battery positive to isolator, isolator to distribution panel and distribution panel to battery negative. There is no sense in making just one short section lighter.

25mm appears to be necessary for the BSS but that clearly expects the engine starter circuit to be wired through the same isolator to the same battery bank as the domestics. If it were not for this 25mm would be far greater than necessary .... 6mm would be adequate and allow you 20 amps before exceeding a 1.5 % voltage drop


I would however site the isolator switch as close to the battery as is reasonable rather than close to the distribution panel.

Also you should incorporate a fuse ( 20 amps would be OK based on what you say ) as close to the battery positive as possible

 

[savageseadog]

For 1.5m of cable there is no point messing around with calculations, just use 16mm cable and you'll be well covered for now and the future. Fitting smaller cable will only save pence.

Good advice. The bigger the better, don't P about.