Cable thickness

[bertiebasset]

Hi, Been increasing my house bank today from single 120 Ah to 2 88 Ahr. The batteries in my Sarum 28 (Aluminium 28') are in the Port cockpit locker. It was 1 house and 1 engine starter in one long box with top level with top of fuel tank. Now have 2 88's in the box and putting the engine in a smaller box on level above above fuel tank (or possibly on top of house bank). Also fitting NASA battery monitor so lots of cables about. The positives from house bank go to position 1 on main make/break switch, the earth going through the 100amp NASA shunt to the earth of starter battery. The starter battery live is smallish red going to position 2 on make/break switch and large (and i mean probably 15 - 20mm thickness) black cable which goes into engine bay. This I assume is to starter but now at home and been thinking ?? How thick does the starter cable need to be ?? It is giving me huge problems just getting it to sit in the new box. I have purchase 2 x 18" cables which are quite flexible and am wondering if they would be man enough to replace. Engine is BUKH 20.
Hoping someone can help
Robert

 

[VicS]

I would expect the negative wire from starter battery to engine and the positive wires from starter battery to isolator switch and onto the engine to be the same size.

Id expect them to be at least 35mm², or AWG 1

I note that the wiring diagram in the manual for the Bukh DV10 and DV 24 engines shows the battery cables as 50mm²

perhaps you should look at the wiring diagram in the manual for your engine.**

**I now have ... 50mm²

 

[William_H]

Heavy wiring

I notice you have trouble just sitting the wire in the box. Like stainless steel wire electrical cable can be a few strands of heavy copper or many strands of fine copper. The one with few strands can not easily be bent and is really made for land type work ie factories where there is not much movement or need to bend tightly. The multi strand stuff is much better for vehicles and boats and far more easily bent if more expensive. good luck olewill

 

[bertiebasset]

Thanks for the replies, I will be back to the boat on Monday/tuesday and will measure them properly.
Vic, Yes you are correct, the starter has one wire to the isolater switch but not sure what the cable is from there to the starter, only thought about it on way back yesterday but will check. There is definately 2 wires from pos side of battery, one red which goes to make/break switch on pos 2 and the other runs into the engine bay, this one black and very very thick. When I get the chance will probably have a re-wire but at the moment just getting my head around all this spaghetti, only had the boat 9 months and sorting out as time permits.
Robert