# 12 volt cable



## 96405 (Sep 29, 2005)

hi all
anyone know a good 12 volt cable supplier? i need to buy it buy the roll not per metre.
cheers in advance


----------



## 96414 (Oct 1, 2005)

Hi

For heavy duty use look up your local welding supplier. for the thinner stuff use an electrical wholesaler.

Beware of getting stuff thats too thin for the job, voltage drop is a nigtmare in 12v circuits, avoid auto electricians and supplies like the plague.


----------



## olley (May 1, 2005)

My local City electrical, sell single 4mm multistrand, which i used to wire up my macerator. I got my 40mm from a firm that repairs injectors, starters and the like, (they are also auto electricians sorry temp)

Olley


----------



## 96414 (Oct 1, 2005)

heh Olly

Auto electricians are OK as suppliers, as long as you the buyer know what you need, for some reason they believe 30Amp cable is actually good for 30 Amps regardless of length.


----------



## stuffed2 (May 9, 2005)

try vehicle wiring products
www.vehicle-wiring-products.co.uk


----------



## 96414 (Oct 1, 2005)

Hi Stuffed

good link, this page http://www.vehicle-wiring-products.co.uk/VWPweb2000/cables/cables.html#gen534 shows why I dont like automotive electricians or their suppliers, note that they claim an ampage for each thickness of wire, this is bad news because of voltage drop. cable thickness needs caculating based on length and ampage that will be used on then can the correct guage of wire be selected.


----------



## 88966 (May 11, 2005)

Hi George,

You are partly correct but the current quoted on cables is the maximum current carrying capacity of that cable (irrespective of length or anything else).

However other factors come into play when actually deciding what cable to use, length which as you rightly say will effect voltage drop, whether the cable is being run in a conduit or trunking and whether that is in air or underground. How many cables are bunched. The type of insulation. There is quite a long list. 

Probably most important in the case of wiring vehicles is to ensure that you are using a multistrand (flexible) cable and if you keep well within its rated capacity you probably will not have to worry too much about length or temperature rise.


----------



## 96414 (Oct 1, 2005)

Hi BillD

Using auto rated cable ampage as a guide is a big no no with regard to voltage drop.

http://www.vehicle-wiring-products.co.uk/VWPweb2000/cables/cables.html#gen534

Lets take the wire *ref 14*

Now it claims rating of 8.75 max, OK you can run that through it, but it will get very warm and waste loads of power.

1mm Cable should really be used for 5 amps max over a max distance of 3 Metres, thats to keep drop under 3% and thats as a minimum

The other problem with auto cable is that the measurement includes the insulation, when you deduct the insulation thickness it would be less then 5 amps (prob not by much on thinwall insulation)


----------



## 88966 (May 11, 2005)

Hi George,

I am not sure what you mean by the dimension includes the insulation ?

The dimension quoted, e.g. 1 mm squared, is the cross sectional area of the conductors - insulation does not come into it.

As I have already explained a lot of other factors do come into play when deciding the actual size of the cable to use. However, to repeat, if you stay WELL with the current carrying capacity of the cable you are unlikely to have problems in wiring a vehicle - the distances are not normally that great. 

Flexibility is most important due to vibrations and the bending and twisting incurred in vehicle wiring.


----------



## 96414 (Oct 1, 2005)

Hi Billd

*I am not sure what you mean by the dimension includes the insulation*

Automotive cable dimensions include the insulation, lets say they are selling 5 mm cable 1 mm can be for the insulation, but you never know unless you check, note they also sometimes say thinwall and oftenm include strands and number of strands


----------



## 88966 (May 11, 2005)

Hi George,

The dimension quoted is, for example 5 mm (squared), not 5 mm.

The site you referred me to quotes:

"General notes on cables.
All cables are made up of a number of strands. Generally these strands are 0.30mm diameter. In our list for each cable we also give the cross sectional area in sq mm, and the continuous carrying capacity in amps. The breakdown of the cable specification 28/0.30mm, 2mm2, 25amps. is as follows:
28 strands of 0.30mm diameter, 2mm2 cross sectional area, 25amps continuous current carrying capacity.

The following equation may prove useful to work out a cable size required. Watts/Volts=Amps."

Insulation does not come into the dimension. It is misleading to some to put incorrect information on here.


----------



## 96414 (Oct 1, 2005)

Hi BillD

Just checked the reference book

Autocable and I quote " autocable is quoted in mm Sq cross section commonly used 4mm cable is actually only 1.8 sq mm of copper the rest is the insulation, unfortunately there is no common comparison between makes"

The other major point here Bill is that yes it may carry the ampage stated but its meaningless with regard to voltage drop, this can only be worked out by using the proper chart and knowing the Copper cross sectional area and the length of the cable run, not the just autocable outside diameter.

This is the cause of many motorhome power problems wire to thin and the biggest cause of that is using autocable and thinking its adequate.


----------



## 88966 (May 11, 2005)

Hi George,

Please would you give me the reference book you quoted from. I am prepared tp learn.

I have searched, both my books and various cable suppliers and nowhere can I find it stated that the insulation is included in the cross-sectional area of the cable.


----------



## olley (May 1, 2005)

George the site that stuffed2 listed quotes 15mm2 with an 8mm O/D that includes the insulation, the 15mm2 is the conductor size.

Olley


----------



## 96414 (Oct 1, 2005)

Hi Olley

Thats why its best to use cable sourced from an electrical wholesaler, guage (OD not including insulation) is the way to calculate voltage drop over any given length.

George

BillD

The reference work is Motorhome electrics (amongst others) by Collyn Rivers.
Here is a link to the guide to 16th edition wiring regs.

http://www.tlc-direct.co.uk/Book/4.3.2.htm

Here is the same 16th edition guide on voltage drop, not that these are high AC voltages which suffer lower drop. But it will give you an idea of the principles involved.

http://www.tlc-direct.co.uk/Book/4.3.11.htm

But I also straight away checked this out at my local automotive retailer, when you measure the stated OD it always includes the insulation, which then means that the usual voltage drop charts do not work.

If you use automotive 4mm you would think its OK for 20 Amps over 3 Meter Max, in reality its only ok to deliver 10 amps over 3 meters (both with max voltage drop of 3 %)


----------



## 88966 (May 11, 2005)

Hi George,

I will state this once more - you do not specify or buy any cable that I am aware of by external diameter including insulation and nothing in the IEE Regs states that you do.

You specify and buy by the cross-sectional area of the conductor(s), ??mm squared, which decides the maximum current carrying capacity. Insulation is a totally additional specification.

Keep telling us that you do and quoting refernces that do not support what you are saying will not change that.


----------



## 96414 (Oct 1, 2005)

Hi BillD

Olley even confirmed OD on the auto cable is including the insulation, go to an Auto store look at the cable measure it where its says 10mm OD the copper will be less and this is the problem. Its easy to prove it to your own satisfaction.

The other problem that is confirmed by the links is that voltage drop is a function of *length, copper OD, and current,* ie my statement that the ampage they quote is meaningless with regard to voltage drop.

If you go to an auto store and ask for 10mm cable see what they bring you, it will be 10mm overall and the copper OD will be less (due to differing insulation thickness its hard to say what size it will be) and this is the main cause of problems its not what people expect.


----------



## 88966 (May 11, 2005)

Hi George,

I am sure that if you asked for 10 mm cable that any electrical supplier would assume you meant 10 mm squared - cable is not sold by OD.

If you spoke to any electrician and said 10 mill cable he would assume you meant 10 mm squared - the trouble is people who know what they are talking about assume others do as well !!

This stream shows that it is not always true.


----------



## 88734 (May 9, 2005)

Here we go again its best to let george have it his way otherwise he will go crying to the moderators 8O


----------



## 88927 (May 10, 2005)

Hi all
Not wishing to enter what appears to be a heated debate I would just like to give the following link for peoples information. I do not suggest I am an expert in these matters as I have forgotten a lot of what I was taught all those years ago. However although the link is not actually MH related it does give some very good information and statistics.

http://www.nmsu.edu/Research/tdi/public_html/pdf-resources/cc80.pdf

I hope you find this useful

Keith


----------



## olley (May 1, 2005)

temporary said:


> Hi BillD
> 
> Olley even confirmed OD on the auto cable is including the insulation, go to an Auto store look at the cable measure it where its says 10mm OD the copper will be less and this is the problem. Its easy to prove it to your own satisfaction.


George i was merely pointing out that they quote both conducter size and o/d.

if i go in to city electric and ask for 2.5 twin and earth i get a cable with 3x2.5mm2 conductors, not a cable 2.5mm in dia.

Olley


----------



## 96414 (Oct 1, 2005)

Hi Bill


From the start here I have said the problem is with Auto cable and the suppliers thereof. Autocable is sold by OD. but that OD includes the insulation, which than means the normal voltage drop charts do not work as they use standard ISO wire gauge (OD of the copper) Electrical suppliers good Auto cable suppliers bad, I think that was all covered in my earlier post.


Merlin 

Your post as usual is designed to goad and is not even worthy of an answer


----------



## DABurleigh (May 9, 2005)

This autocable supplier is crystal clear, George.
http://www.autoelectricsupplies.co.uk/file_uploads/aes_catalogue_3.pdf

Dave


----------



## olley (May 1, 2005)

Sorry george misunderstood, as i do not buy from auto electric shops i do not know how they size wire. seems a very odd way to sell cable though  

Olley


----------



## 89122 (May 14, 2005)

George, why the name change.

It seems to me that as long as the copper part of the cable is as thick and flexible enough for the required load on it thats all that should matter.
quoting all the technical parts is going to confuse the average non electrician.
So it is best to keep it as simple as possible in my opinion.

This is not meant to contradict anyone.

happy short circuits.
Eddie


----------



## 88927 (May 10, 2005)

Thanks Dave
Some of the stuff on there looks brilliant and at better prices than R.S.
Many thanks

I also hope morrmorr that you feel that you have had an answer mate !!!!!!

Keith


----------



## 89122 (May 14, 2005)

morrmorr only wanted to know where to buy cable,lets hope this has helped him.

Eddie


----------



## 96414 (Oct 1, 2005)

Hi Olley 

My post quoting what you were saying was not well put, what I am trying to get accross here is that Auitocable is poorly described, 4mm Sq from an electrical supplier is 4mm sq copper, however if you were to use 4mm Sq autocable it would be roughly 1.8mm sq copper an the rest would be insulation.

Now If BillD were to order a roll from an Auto supplier he would notice straight away that the copper was too thin. Many non electricians here would not know.

No lets say someone were to reccomended 4mm cable to be used on a 20 Amp circuit of under 3meters, if the person were to go to an auto electrician he would be given what we consider 1.8mm cable ie it would be wholly inadequate, that is why I keep saying avoid Autoelectrical cable and or suppliers.

I should not have mentioned OD its totally wrong context, my meaning was that the overall measurement included insulation.

It is a damned odd way to size hence all the confusion here, I hope the above is much clearer.

Hi Rapido

Simple is good but the differing guages and system cause a lot of problems and is the main cause of motorhome related electrical troubles. Hope the above claruifies why.
Temporary is temp until Nuke finds the problem with my original account, Nuke as more than enough things going on at the moment to be chasinfg this minor glitch up.


----------



## 96088 (Aug 22, 2005)

rapido said:


> morrmorr only wanted to know where to buy cable,lets hope this has helped him.
> Eddie


Perhaps he should have asked where to get a tin hat instead :lurk:


----------



## 88927 (May 10, 2005)

LOL at oldskool :lol: :lol: :lol: :lol: :lol:

Maybe he should look up this http://www.ealdormere.sca.org/heraldry/tinhats.shtml
To find out what sort of hat he would prefer......
:lol: :lol: :lol: :lol:

Keith


----------



## RobinHood (May 19, 2005)

Are they sized by the diameter of the head.....or the diameter of the hat?

8) 8)


----------



## spykal (May 9, 2005)

I have been ready this thread with avid interest and all I can add is

I was always told..."If you can't fight wear a big hat"........

My head is hurting .......Can I have my counselling now please nurse? :lol: 

mike


----------



## 96405 (Sep 29, 2005)

wow guys i am impressed and also confused lol, can someone answer this then? i have a max run of 4 metres can i just use realy thick cable for everything? or can someone tell me what thickness cable i need for lights, 12 volt sockets . and the 12 volt from vehicle ignition to fridge. also am i right in thinking the thicker the cable the less resistance it has hence beter for currant draw?
regards to you gurus :-D


----------



## 89122 (May 14, 2005)

Wait for it-----------------------------------------here we go again

Eddie


----------



## RobinHood (May 19, 2005)

Without getting drawn into the previous argu.... sorry debate, I decided to look at the installation manual for my fridge.

It draws (at spec) between 14 and 15 amps on 12V.

Dometic recommend 6mm (squared) cable up to 6m in length, and 10mm (squared) above (obviously an upper limit on this, but how long a run do you need an a 'van?).

The above is the cross section of the cable (excluding the insulation). You can make clear what you want wherever you buy it, and whatever they sell it as. 

Gives you a reasonable starting point as a 'rule of thumb'.


----------



## 96414 (Oct 1, 2005)

Hi Morrmorr

Lets say the fridge is 15 Amps as per Robins post, 6mm Squared is actually good for 30 amps at 3 meters, its good for 15 amps at 7.5 Meters

10mm is good for 30 amps at 3meters and 20 Amps for 10 Meters, so Dometics reccomendations are good.

if you list a name, Ampage and distance (there and back dont forget the negative return path) I will post the reccomended gauge wire.

so say Light, 4 metres 16 watt (1.5 amp nr enough) would be OK with 1mm sq 

say TV socket, 5 metres (2.5 meters from battery), 50 watts (4 amps nr as) would need 1.5 mm sq minimum, I would go with 2.5 mm so that if the battery is low and say another high drain item cuts in, then the tv is less likely to be effected.

Invertor 600w 1 ft (max ampage continuous is 50) 10mm sq as min.


----------



## 96405 (Sep 29, 2005)

thanks a lot guys you are all very very helpfull indeed, i will measure the van tomorrow and post what i need in the evening. i will drive in my van and buy you all a pint in your local when its done :-D


----------



## 88927 (May 10, 2005)

There, another satisfied customer.....
That was easy enough wasn't it?????

:lol: :lol: :lol: :lol: :lol: ccasion5: 

Keith


----------



## Scotjimland (May 23, 2005)

kands said:


> There, another satisfied customer.....
> That was easy enough wasn't it?


Well, I can't wait for the debate on charging :violent1: :wink:


----------



## PhilM (May 9, 2005)

I think you'll find the debate on charging ( for membership ) going along another thread :lol: 
Phil.


----------



## Scotjimland (May 23, 2005)

PhilM said:


> I think you'll find the debate on charging ( for membership ) going along another thread :lol:
> Phil.


Yes indeed, think I'll take a rain check :wink: :lol: :lol: :lol:


----------

