Need help with wire size please.

[Gozz]

Hi guys.
I'm about to install a switch panel and I'm not sure which size wire to run to replace the old wires.
I'm thinking 2 or 3mm copper tinned wire which works out to about 9amp for the 2mm and 16mm for the 3mm.
Most of the wires run led lights, sounder, gps and one for the bilge pump.
Thanks for your help.

[scottar]

With marine wiring you are better off going for at least 3mm but personally I use 4mm for low current devices - gives you a bit better safety net to cope with vibration IMO. Also less voltage drop. Use something like a 6mm as the supply main for the panel with a suitable fuse close to your battery/battery switch. Heavier wire will also last longer should it happen to get wet.

[rayken1938]

what is the current draw of the bilge pump some of the larger ones draw around 10 amps.
cheers
ray

[Gozz]

Thanks guys.
Thanks Scott ill use at least 4mm, I was looking at the amp size over the mm size which is why I thought 2 to 3mm was enough.
The bilge pump I'll run seperate wires and one 6mm wire going into the isolater switch to feed the switch panel.
Does this sound right.
Thanks sgain.

[scottar]

That sounds right. 6mm positive feed via the isolator with a good waterproof fuse at the isolator, 6mm negative to a busbar or post near the panel, 4mm twin from these to all accessories using the right size fuses for the respective accessory at the panel if it has them incorporated or in a separate fuse block beside the panel if not (keeps them all in the one spot so you don't need to go hunting for in line fuses if there is a problem). All cables should be tinned. Ensure all wires are protected anywhere there is a potential for chafe - especially if the hull is aluminium. Any joins for bilge pumps need to be sealed with either glue filled heat shrink, self amalgamating tape or both and secured above any likely water level for longevity - don't just leave them lying in the bilge. It's a good idea to seal any other joins as well even if they are under the dash.

[outwide1]

I ran 4mm through out the build of Outwide.
I opted for 6mm on the heavier drawing items like the fridge and light bar.
I had a heap of battery size cable left so I used that to power up the main buzz bars feeding all the fuse boxes.
Mick.

[Gozz]

Thanks guys.
When ever I do a electrical join I put a heat shrink over the joint then I fill with silicon then I put the heat gun over it until the silicon starts to come out each end.
I've done this for years and so far so good.

[Fed]

Current carrying capacity tables can be pretty misleading for 12V, you are better off using voltage drops to work out your cable sizes.

[Gozz]

Thanks Fed.
I just remembered my mate is a electrical fitter.
Might have to bust his nuts. Haha