12v cable size

Swampsnake

Forum Member
Hi all. I'm wondering what size cable I should use. I've been watching you tube videos and the preferance seems to be 2.5mm H07RN-F 2 core, which I've ordered. But this cable is 10mm thick in total and seems way overboard and according to the seller is for 230/240v. Is this the correct cable or have I bought the wrong stuff? Any help appreciated.
 

Squiffy

Forum Member
It really depends on what 12volt systems you intend to power up. Cable sizes can vary by which circuit your wiring
I.e. wether it's current heavy like battery feed or current light like LED lights. You would have to give much more information than just 12v cable size required. Phil
 

Swampsnake

Forum Member
Thanks Phil and Mark. My plans are for 4 12v lights, one which is a strip of LED's which forms part of the skylight, and three others, 1 over the kitchen area, 1 over the dining area and one over the bed. I don't have them yet but they will be the most energy efficient I can get. 2 12v USB sockets and 1 12v power socket. apart from a battery moniter cable, thats it. I'll be having a compressor fridge which i know will need a more substantial cable. The thing which has surprised me is the overall thickness of the cable i've bought for the above, which is 10mm. It may have something to do with voltage drop but i know nothing about electrics and I wont be wiring anything myself. I was just putting the cable in place so I can crack on with the build.
 

Merl

Forum Member
Cable guage is dependent according to the current it's going to carry (so you need to establish that first, if you only know the wattage then divide that figure by 12 to give you the current in amps.)it's total length and whether it runs through insulation. 12volt planet has a decent calculator to help with this.
It's normal to run separate circuits to the various loads so possibly 3 circuits for the above but certainly run a dedicated run to the fridge.
LED lights use very little so the cable guage requirements will be thin, slightly larger for the USBs and larger still for the fridge.
For some reason lots of low voltage cable seems to have thicker insulation than a lot of mains rated cable resulting in an overall size that seems unnecessary thick! You can use high (mains) voltage cable for 12V supplies if you want but you introduce the possibility of confusion later down the line if you use brown and blue for the 12V side, personally I'd stick to brown/blue for mains wiring and red/black for 12V. Either way ALL cables should be multi stranded (flex) you shouldn't use solid core.
Make a drawing of where they run and keep it safe ( you will almost certainly refer back to it sometime in the future) and protect the cables from chafing against the metal body around corners or through holes.
 

Squiffy

Forum Member
What Merl says is good advice, though I have to say on several builds I've used mains flex split out of the casing using blue for neg and brown for pos 12v mainly because I had reels of it available f.o.c. But as stated I've had to tag the wires both ends to state what it's for.
One other thing is regardless of current and wire size a fuse of correct rating should be placed close to the power source in each feed wire, as led may not take much current but if the LED feed wire short cct's then that wire suddenly heats up with every amp your battery can supply hence a red hot wire till it burns out. Phil
 

Swampsnake

Forum Member
Thanks Merl & Squiffy and sorry for the late reply. I've looked at the 12v planet calculator and it seems the cable i've bought is more than enough for my 12v needs, excluding the fridge. I'll just have to get some wider diameter conduit. Each item will be wired individually and i'll defo make sure fuses are fitted.
 

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