# Will 1 sq mm cable be man enough?



## Glandwr (Jun 12, 2006)

Hi while re-bedding a window in the van I discovered loose but insulated 12v and 230v terminals under the false floor of a cupboard (factory fitted I suspect for a TV). 

I want to fit an extra double 12v socket next to the passenger seat and this lead will let me do it. It will be used mainly for charging laptop, MP3, sat nav, and the phone when it is acting as a hotspot for tethering.

I’ll put a 10amp inline fuse, as I don’t want to have to find the other fuse if something goes wrong.

My question is will a twin 1sq mm cable (which I have) be sufficient for the run (approx. 1.5 mtres) or should I go bigger. 

Many thanks Dick


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## olley (May 1, 2005)

1mm and 1.5mm cable is normally only used in lighting circuits, and is usually protected by a 6amp fuse, I would use 2.5mm.

Ian


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## GEMMY (Jun 19, 2006)

2.5 mm is for a house ring main, 3kw + 

tony


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## Glandwr (Jun 12, 2006)

Thanks Olley those are the norm for fixed domestic wiring as Tony says. But I’ve got a 25mtr extension lead fused at 13amp that is CE stamped and is rated at 2,400 watts at 230v that is 1 sq mm. Now I know that 10amps at 12v will need more. But on the other hand the things that I am thinking of using will no way draw anything like that even in all together. The fuse is there in case of momentary short circuit.

Trouble is these cigar lighter chargers don’t seem to have much info.

Anyone know what phone + mp3 + laptop would draw all on together?

Dick


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## rosalan (Aug 24, 2009)

If its any help, the power drawn should show on your laptop transformer, my Netbook requires 1.2 Amps and I guess that the other two items are negligible, so let us say 2 amps to be safe. A 2.5 cable should be safe to use.
As for your using a lighter weight extension, this may be ok with loads of cool air around it but as stated 2.5 should keep cooler and so safer.
Is this not why we should always unroll the whole cable when on hook-up?
Alan


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## listerdiesel (Aug 3, 2012)

1mm would be OK with a smaller fuse, 5A would be OK and would cover all of your devices.

If you want to use a 10A fuse, then go up to 1.5.

2.5 if the run is over a couple of metres.

I used 1mm twin for most of the lighting & control stuff in the trailer, but fused accordingly. When I get a minute (!) I'm going to take the twin out an rewire with 1mm or 1.5mm singles, depending on what is at hand or I can pick up cheaply. 

Nicest 1mm stranded is Def Stan 61/12 Type 3 which has an extra thick sheath and is what we use at the factory.

Peter


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## CliveMott (Mar 10, 2008)

For the loads you mention 1 sq mm should be fine. A 10A fuse would protect the wiring. Just remember that your orange hookup lead is 1.5 sq mm and carry's up to 16 amps. 

But use a 6A fuse if you like as your loads are all quite small.

What is important to remember in 12 volt circuits is the cable VOLTAGE DROP under load. Losing 2 volts when the supply is 240 volts is insignificant. Losing 2 volts when you only have 12 to start with is very significant.

Take care.
Use a professional if you are not sure.

C.


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## selstrom (May 23, 2005)

Chart here says 1.5 mm;

http://midsummerenergy.co.uk/solar-panel-information/SolarPanelWiringDiagrams/CablesAndFuses


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## CliveMott (Mar 10, 2008)

Yes it does and that is just one chart designed for low voltage solar panel wiring. It is not incorrect.

Lots of other parameters come into play and the most important with 12 volt systems being volt drop. 
But the cable rating also changes when there are a number of conductors together in a sheath, or in a conduit, the type of insulation, the thermal stress on the other conductors etc.

But the posting said two cores and your hookup lead is actually 3 cores in a sheath although 1 core does not actually carry current unless under a fault condition.

Nothing is as simple as it first appears!!

Your hookup lead is a good example of this although hookups longer than 25M should be 2.5 sq mm, not two 25M leads plugged together! Volt drop again

C.


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