Electrics First Fix

[Leighjcj]

Evening all,

Just after a little advice/input as I'm just in the throws of getting the wiring etc. in place.

So it will be leisure battery to fuse box, then to switch panel on to load that I need a little help with.

Fuse box is 12way so room to split loads if that's recommended.

Roof lights and tailgate lights are sorted.

1) I'll be installing 3 x twin USB sockets (twin 2.1a), so 4.2a per socket and maximum total of 12.6a on the circuit. For this am I right in thinking 1.5mm2 cable with a 15a fuse?

2) I'll be installing 2 x 12v sockets and has based a worst case of 10a per socket (tyre inflator for example) so 20a on this circuit. Would 2.5mm2 cable with a 25a fuse be right?

3) From leisure battery to fuse box.. I've worked out that maximum load (everything on and being used) is around 35a, so would a 10mm2 cable with a 40a midi fuse be the best option?

I've read through tons of posts and threads. the guides on here have been invaluable. I just want to make sure I don't miss anything and get my calculations wrong.

There will be (at some point) a fridge and water pump to add but these will be on their on cables/inline fuses.

Cheers

 

[The Bear78]

Have a look at the chart in post #17 of this thread. it details amp ratings by cable cross section (if you haven't seen it before).
10mm is probably excessive for a 40 amp fused circuit but at least it will be future proof.
As you know it should be load-fuse-cable in terms of rating ie. 10 amp load, 15 amp fuse and 21 amp cable (1.5 mm) or whatever the next highest is in each case.
Don't forget voltage drop either as this will increase the load.

 

[Leighjcj]

Thanks @The Bear78, yes I know that thread well

Yes the 10mm was really to cover future additions really. No harm I thought. (Plus I've got some spare haha)

Yep the cable loads are factored in to the cable selections so should be covered however I might need to do a bit more reading up on the voltage drop though to make sure.

Cheers

 

[The Bear78]

Yep. It's a good read!
Voltage drop is unlikely to be a large amount but you will run into situations where the extra few milliamps will just tip you into the next fuse and/or cable size.

 

[Leighjcj]

I’ll have to get the calculator out again now to be sure

 

[Grim Reaper]

There's a handy calculator on the bottom of this page..

Cable Size Calculator - Cable sizing and selection | 12 Volt Planet

Cable Size Calculator - Read our guide to selecting cable of the correct type and size for your automotive, marine or leisure wiring application. Auto and Marine Electrical Components from 12 Volt Planet

www.12voltplanet.co.uk

The lower you can get the voltage drop the better, the only limits are how much you want to spend and how much room you have for the cables.

 

[Leighjcj]

There's a handy calculator on the bottom of this page..

Cable Size Calculator - Cable sizing and selection | 12 Volt Planet

Cable Size Calculator - Read our guide to selecting cable of the correct type and size for your automotive, marine or leisure wiring application. Auto and Marine Electrical Components from 12 Volt Planet

www.12voltplanet.co.uk

The lower you can get the voltage drop the better, the only limits are how much you want to spend and how much room you have for the cables.

Thanks mate

 

[Grim Reaper]

I bought 2 reels of 24/0.2mm 18AWG/0.75mm2 wire from CPC https://cpc.farnell.com/concordia-t...-24-0-20mm-black/dp/CB19907?st=equipment wire which I used for pretty much all of the low current items in my van (LED lighting / USB chargers) up to 6A.
For anything above that (Diesel Heater comes to mind) I used 26/30AWG 16AWG 1.3mm2 https://cpc.farnell.com/alpha-wire/6716-bk005/wire-eco-16awg-black-30-5m/dp/CB16574
For Starter to DC/DC charger and Leisure battery and Inverter interconnects I used Twinflex 16mm2 6AWG https://www.altecautomotive.co.uk/t...bles-bonded-together-in-a-figure-8-4118-p.asp via SB50A Andersen connectors where appropriate for disconnects and suitably rated midi fuses https://www.ebay.co.uk/itm/18340711...il&pgrp=main:email&e=op&mchn=em&s=ci&mail=sys
The fuse box https://www.ebay.co.uk/itm/11259142...il&pgrp=main:email&e=op&mchn=em&s=ci&mail=sys is fed via a battery cut off switch https://www.ebay.co.uk/itm/100A-BAT...354868?hash=item54945caeb4:g:T-EAAOSwNJxfK53r so everything can be isolated in one go.
I made a hydra cable up from 10 short lengths of the 16AWG wire from a ring terminal to Lucar connectors to feed the fuse box terminals.
Buy or borrow a set of hydraulic crimpers for the big terminals https://www.ebay.co.uk/itm/10-Ton-9...222886&hash=item4b8b3b7b13:g:WM8AAOSwwqpgCANZ and I found blank ring terminals were the best thing because I could use them on whatever I needed them on. I can't remember where I got them from but I used almost a whole packet (20ish)

 

[Leighjcj]

Thanks @Grim Reaper this is a great bit of info