12v wiring

Hymer544

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12v wiring

· Posted: 10.07.2019 · #1

Hi...what's wrong with using 7 score 2.5mm wire for 12v electrics....its flexible enough to travel through conduits and easily cable of handling any current loads required in camper...its 18p per meter compared to about 90p for multistrand equivalent,??

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Re: 12v wiring

· Posted: 10.07.2019 · #2

The type of cable used, especially in low voltage wiring like 12v is important... voltage drop and loss over a given length being the concerns.
Multi-strand high efficient cable will suffer much less loss than cable designed for other applications.... although the other will work, the circuit efficiency will be compromised.

The Rambler

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Re: 12v wiring

· Posted: 10.07.2019 · #3

Quote by Hymer544

Nothing necessarily. It depends on what kind of load you want to wire. The more strands or cores in a given diameter, the less current carrying capacity. Obviously stranded 25mm² carries less current than single core 25mm², but is much more flexible and easier to work with.

What is the spec. on your cable, i.e. current capacity, resistance per meter etc.? If you don’t know just confirm the dimensions again. Is it 2.5mm² per core, and 7 cores in total? And finally, what is the highest current you expect to supply in your setup? Remember, you can run very light quage wire to certain tiny loads like an led light, but you will want to run heavy guage for split charging etc.

Hymer544

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Re: 12v wiring

· Posted: 10.07.2019 · #4

Hi rambler. Split charging, inverter and B2B are all sorted with heavy duty wire. Im just looking at wiring to run through roof for 2 roof fans, LED spots and a few USB charging points. I already have three core 240 wire routed for the 240V and inverter 240V sockets. The largest draw will be 3.5 amps for a 40W compressor. Ive tried every cable supplier in my area and none of then have multistrand wire so Im tempted to strip standard three core domestic cable and use it or use the 7 strand 2.5mm wire that \i can get locally.

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Re: 12v wiring

· Posted: 10.07.2019 · #5

Quote by The Rambler

Quote by Hymer544

Jason, I think you’ll find stranded cable has a higher current carrying capacity than solid cable, especially multi stranded

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Re: 12v wiring

· Posted: 10.07.2019 · #6

Are you sure about that David? Are we talking about the same thing? The current capacity is proportional to the cross sectional area of the conductor(s). In stranded cable there is space between the strands therefore it contains less copper per unit area than a solid core, therefore less current. That’s true for DC anyway. In AC we get the skin effect at high frequencies where most of the current travels on the outer surface of the conductor.

Either way, in Hymer’s case I think the difference is immaterial between 7-core or multistranded, providing the current capacity is there.

Thorn123

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Re: 12v wiring

· Posted: 10.07.2019 · #7

Quote by Hymer544

You should never use domestic cabling for 12 volt DC .
12 volt DC can produce alot of heat under a load and domestic cable sheathing is not able to withstand the higher temperatures.
I use 2.5 mm2 cabling in work everyday at auto stuff and it's 28 strand and it amp capacity is 17.5 amps for the first metre run.
Obviously it's capacity drops by a percentage or two per metre afterwards.
But I am confused with you mentioning 7 strand 2.5 mm2.
Do you mean 7 core cabling as in trailer light cabling?
If so the heaviest version of such that I have seen is 6 core of 1mm2 and the 7th core of 2mm2,which is the earth.

Daffysparks

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Re: 12v wiring

· Posted: 10.07.2019 · #8

Quote by The Rambler

I can’t put my finger on it right now, but yeah. A multi stranded flex has a higher current carrying capacity than a solid. Possibly something to do with the amount of surface,as you suggested. 27 strands= a lot more surface than 1 solid. But in the regs. Our bible, definitely. Higher capacity on stranded than solid.

Hymer544

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Re: 12v wiring

· Posted: 11.07.2019 · #9

hi thorn, an electrical supply outlet gave me a sample of 7 strand copper wire 2.5mm2 today. Its flexibility was ok but not as flexi as 28 strand obviously 3 core flex. I really cant see how multistrand flex 2.5mm2 wires from domestic 3 core flex would not do the job....after all my highest current draw appliance would be a 40W compressor fridge at 3 Amps. I have 25meters of 3 core flex that I can strip out the brown and blue wires from and use them...Thats my query really.

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Re: 12v wiring

· Posted: 11.07.2019 · #10

I have to check with you hymer as I think there is some potential confusion with regards to multicore/ multi-strand terminology, which could explain myself and Daffy getting our ‘wires crossed’ ( sorry about that, couldn’t resist).

But is your cable, I’ll just say ‘7-way’ for the moment, like the first pic below or the second pic below? One is multicore, and can essentially carry 7 different power lines or signals as each core is insulated. The PVC insulation of each core will reduce the overall current capacity as heat cannot dissipate so quickly. The other is a single core made from 7 strands of copper.

I should point out that in the first pic, each of the 7 cores are themselves multistranded, but don’t let that confuse you, they could just as easily have been solid cores.

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Re: 12v wiring

· Posted: 11.07.2019 · #11

Don't be afraid to up-rate your cables.
More importantly, never forget to fit the appropriately sized/rated fuses and connections!

Here's a good read:
https://www.everythinghamradio…the-power/

12V wire selection

Hymer544

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Re: 12v wiring

· Posted: 11.07.2019 · #12

hi rambler. I referred to 7 strand, as in 7 copper strands. Not 7 cores as in trailer cable. I am pretty sure that I will use 28 strand brown and blue from standard 3 core flex due to:

1 its capability to handle my current draw and powers
2 availability of 3 core flex
3 flexibility and easy of routing
4 cost

I remain to be convinced that 28 strand red/black 12v wire is absolutely necessary and any better than 28 strand domestic 2.5mm2 wire. If I could get it that locally and didnt have to pay silly shipping costs from UK I would use the so called '12V' wire. I am of course willing to bow the better knowledge than mine and if I am missing something obvious and foolish?

Daffysparks

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Re: 12v wiring

· Posted: 11.07.2019 · #13

If your largest draw is 3.5 amps and you are using 2.5 mm cable, as long as the cable run isn’t enormous, I can’t see any problem with using standard flex.

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Re: 12v wiring

· Posted: 11.07.2019 · #14

I’m with you Hymer. Are you going to strip it from the flex and if so how? Stanley knife? Been there, done it. It’s a right pain. And tricky to avoid nipping the brown or the blue

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Re: 12v wiring

· Posted: 11.07.2019 · #15

Fair play lads, I now feel like an experienced electrician after all that explanation.
I still think that I will leave it to the experts.

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Re: 12v wiring

· Posted: 11.07.2019 · #16

Quote by The Rambler

I’m with you Hymer. Are you going to strip it from the flex and if so how? Stanley knife? Been there, done it. It’s a right pain. And tricky to avoid nipping the brown or the blue

If you split about 150 mm with a knife, then one of these should work
1: catch all three strands in one hand, outer sheath in the other, and pull apart at approximately 45° angle.
2: if No.1 doesn’t work. Start the same, then hold one core in one hand and outer sheath in the other and pull approximately 150-200 mm free. Observe which core is now nearest your split and pull that one the same. Then core 3, and repeat. A bit of a pain, but will strip out with no damage... unless your built like Mr Universe

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Re: 12v wiring

· Posted: 11.07.2019 · #17

Very true Daffy!

Thorn123

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Re: 12v wiring

· Posted: 11.07.2019 · #18

I have been thinking about this topic and came to a different opinion.
Since its internal wiring and away from the usual auto environment, domestic flex will work.
However I won't strip out the outer sheath or remove the earth cable.
The outer sheath will help to prevent abrasion while not removing the earth cable, leaves you with future options of adding more lights etc.

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Re: 12v wiring

· Posted: 11.07.2019 · #19

I think you’re right Thorn. A lot of the usual rules about heavy guage battery and alternator auto wiring under the bonnet goes out the window on the habituation side the in campers.

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Re: 12v wiring

· Posted: 11.07.2019 · #20

I've a roll of rusty barbed wire, could I use this and cover it with tape

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Re: 12v wiring

· Posted: 11.07.2019 · #21

Quote by eirebus

I've a roll of rusty barbed wire, could I use this and cover it with tape

That really depends on what you’re into eirebus

. No judgment here. Each to their own, as they say

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Re: 12v wiring

· Posted: 12.07.2019 · #22

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on 12v wiring

· Posted: 12.07.2019 · #23

The simplicity of it all, a few coat hangers and a bit if auld garden hose to stop it shorting out.

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Re: 12v wiring

· Posted: 23.07.2019 · #24

Late to the show but if your total draw is 3.5a you might be OK with the thinner coated (plastic coating around the wire) 2.5mm2 cable. That said if your running the 40w compressor, LEDs and a couple of USB ports charging phones at 2.1a each you could be up to nearly 10a total. In that case I'd order 12v wire online or pop into Halfords and get their 17a or 28a cables (as expensive as they are). No harm in getting the thickest cable you can to avoid voltage drop. Eg. France last week in your old Knaus Traveller I couldn't power a cooler box off one of the 12v sockets. Too much of a voltage drop and the cooler box thought the batteries were low.

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