What size 12v cable?

[Nightwatch]

Hello. I have asked this before about a year ago and can't remember the advice nor can I find the thread.

i am moving the telly to a different position. Want to run cable from existing 12v socket to a new socket where the telly will be. By the time it has gone up the bulkhead and over doors and down to the new location it's going to be about 5 metres. 

What size cable would I need. Also, I asked, in a small hardware shop, for some 12v cable and was told they don't sell it. Is 12v cable Different to 240v cable! 

Thanks.

[john6767]

7 minutes ago, Nightwatch said:

Hello. I have asked this before about a year ago and can't remember the advice nor can I find the thread.

i am moving the telly to a different position. Want to run cable from existing 12v socket to a new socket where the telly will be. By the time it has gone up the bulkhead and over doors and down to the new location it's going to be about 5 metres. 

What size cable would I need. Also, I asked, in a small hardware shop, for some 12v cable and was told they don't sell it. Is 12v cable Different to 240v cable! 

Thanks.

I have used multi strand stuff from B&Q intended for mains, just make sure that you work out the power rating as something marked as 5A will be 5A at 240V, and you need it at 12V.   For the cable size you just need an acceptable voltage drop and you can use a calculator like this one https://www.12voltplanet.co.uk/cable-sizing-selection.html

[Sea Dog]

Have a look at the single or twin stranded cable sold for vehicle wiring, which is the right stuff - I've bought at good prices on ebay. Some recommend the version that's been tinned, but arguably you don't need to go to the extra expense on a dry fresh water boat.

Google will find you a volts drop calculator (oh, hang on, there's a link from John above!).  Remember to take into account the length and cross section of the run you're extending.  You may need to consider a new run in toto.

[Tony Brooks]

5 amps is 5 amps, it matters not if its at 12 or240 volts. Its the amps that does the heating and consequential voltdrop.

The only think that MIGHT differ between 12V and mains cable is the mains cable will have insulation capable of holding in mains voltage so as long as its true multi-strand cable (e.g. not the old three strand per conductor domestic stuff) mains specified cable will be fine.

Can't give you a minimum cable size until I know the current (amps) that may be drawn from the socket. I assume that you mean the total cable run out and back is 10 metres. A quick calculation based on a guessed 3 amps current suggest 2 sq mm CCSA would give a voltdrop of a fraction over 0.2 volt but oyu need to add the voltdrop on the existing cable to that so perhaps go for 3 or 4 sq mm CCSA..

 

[john6767]

9 minutes ago, Tony Brooks said:

5 amps is 5 amps, it matters not if its at 12 or240 volts. Its the amps that does the heating and consequential voltdrop.

The only think that MIGHT differ between 12V and mains cable is the mains cable will have insulation capable of holding in mains voltage so as long as its true multi-strand cable (e.g. not the old three strand per conductor domestic stuff) mains specified cable will be fine.

Can't give you a minimum cable size until I know the current (amps) that may be drawn from the socket. I assume that you mean the total cable run out and back is 10 metres. A quick calculation based on a guessed 3 amps current suggest 2 sq mm CCSA would give a voltdrop of a fraction over 0.2 volt but oyu need to add the voltdrop on the existing cable to that so perhaps go for 3 or 4 sq mm CCSA..

 

You are right of course, I should have said Watts!

[Bazza954]

I've used these suppliers before for cable http://www.vehicle-wiring-products.eu/?jssCart=2e7c65a567a9815b76db38fe606a309b

They sell the tri rated cable

[Tony Brooks]

12 minutes ago, Bazza954 said:

I've used these suppliers before for cable http://www.vehicle-wiring-products.eu/?jssCart=2e7c65a567a9815b76db38fe606a309b

They sell the tri rated cable

For goodness sake IGNORE tri-arted or thin wall cable specifications amp wise and only go by CCSA. The amps rating is only concerned with the propensity for the cable to catch fire/shed heat. Tri-rated cable will produce the same voltdrop for any given load and length as any other type of cable Its main advantage is that it tends to be thinner so more can got through a given hole - not so important on boats.

If Tri-rated is cheaper or its the only time available in the CCSA you need then fine but do not think it can SATISFACTORILY carry higher currents than standard PVC. IOt wont, the voltdrop will be the same CCSA for CCSA.

[Alan de Enfield]

Tri-rated is a wonderful marketing ploy - it purely means that it meets UL (Underwriters Laboratories) , CSA (Canadian Standards Association) and BS (British Standards) requirements (and as they are all pretty much the same specification it is not difficult)

TRI-rated cables is 'nowt-special'.

[Bazza954]

11 minutes ago, Tony Brooks said:

For goodness sake IGNORE tri-arted or thin wall cable specifications amp wise and only go by CCSA. The amps rating is only concerned with the propensity for the cable to catch fire/shed heat. Tri-rated cable will produce the same voltdrop for any given load and length as any other type of cable Its main advantage is that it tends to be thinner so more can got through a given hole - not so important on boats.

If Tri-rated is cheaper or its the only time available in the CCSA you need then fine but do not think it can SATISFACTORILY carry higher currents than standard PVC. IOt wont, the voltdrop will be the same CCSA for CCSA.

 

3 minutes ago, Alan de Enfield said:

Tri-rated is a wonderful marketing ploy - it purely means that it meets UL (Underwriters Laboratories) , CSA (Canadian Standards Association) and BS (British Standards) requirements (and as they are all pretty much the same specification it is not difficult)

TRI-rated cables is 'nowt-special'.

I've just checked on their site and they don't appear to stock this cable now, can't have caught on. !!

[W+T]

I reckon 3mm or better still 4mm. 

 

Have a look here. All three is to know and need.

https://www.12voltplanet.co.uk/

 

 

 

[ronnietucker]

I have some cable, suitable for 12V and cars, which is rated at 6A.

I'm going to run some cable from an existing cigarette socket to another one about 6ft away. 

What would happen if I plug my 12V hoover, rated at 6.7A, into this second socket? Warm cable? Melted cable? Nuclear meltdown? End of all humanity?

[rusty69]

3 minutes ago, ronnietucker said:

I have some cable, suitable for 12V and cars, which is rated at 6A.

I'm going to run some cable from an existing cigarette socket to another one about 6ft away. 

What would happen if I plug my 12V hoover, rated at 6.7A, into this second socket? Warm cable? Melted cable? Nuclear meltdown? End of all humanity?

What is the fuse rating to the socket?

[ronnietucker]

1 minute ago, rusty69 said:

What is the fuse rating to the socket?

Ah. I'm glad you asked.

Sorry. I've no idea. I've never checked the fuse.  

[Murflynn]

On 22/03/2018 at 21:23, W+T said:

I reckon 3mm or better still 4mm. 

 

Have a look here. All three is to know and need.

https://www.12voltplanet.co.uk/

 

 

 

pedant alert!! 

how do you measure cable in mm?  is it diameter, circumference or what?

[Tony Brooks]

32 minutes ago, Murflynn said:

pedant alert!! 

how do you measure cable in mm?  is it diameter, circumference or what?

Its shorthand as you know. Its a lot of typing to get it right - 3 or 4 sq. mm conductor cross sectional area, so people just say mm and drop the sq. or superscript 2.

13 hours ago, ronnietucker said:

I have some cable, suitable for 12V and cars, which is rated at 6A.

I'm going to run some cable from an existing cigarette socket to another one about 6ft away. 

What would happen if I plug my 12V hoover, rated at 6.7A, into this second socket? Warm cable? Melted cable? Nuclear meltdown? End of all humanity?

First of all if all cable suppliers stopped giving a current rating things would be better. OK, in your case you are talking about a 4 metre run so for most things that 6 amps may not be far out BUT the voltdrop along the whole cable run is far more important. Especially with things like motors that increase their current draw as they slow down so can burn out with undersized cable - or even burn the cables.

Nominal 6 amp cable probably has a CCSA of 0.25 sq. mm so you are talking bell or speaker wire. Nominal 11 amp thin wall cable has a CCSA of 0.5 sq. mm (VWP 2016 catalogue). Once you get to that type of small size you are likely to have less than the ideal number of strands so each strand will be thicker and more likely to fracture. Standard PVC cable with a CCSA of 1 sq mm is rated at a nominal 8.75 amps and it has insufficient strands for the ideal so again nominal 6 amp cable will be thinner.

If that 6.7 amps is the continuous rating then the current will be at least a third higher as the motor starts. Ignoring the fuse question the cable will get warm, especially if it is in a confined space so it can not get rid of heat. This could eventually lead to the conductors pushing through the insulation but at just a 0.7 amp overload I doubt this will happen. If there as an electrical fire then using that cable gives the insurance company a potential get out of jail free card. If that 6.7 amps is the peak start up current then although poor practice pragmatically I think the cable will be fine. However for a few quid I would buy something thicker.

[Alan de Enfield]

21 minutes ago, Tony Brooks said:

Once you get to that type of small size you are likely to have less than the ideal number of strands so each strand will be thicker and more likely to fracture.

'Domestic' flexible wires (to BS6500 or EN equivalent) are 

0.5mm2 = 16 strands, each strand 0.2mm diameter - written as 16/0.2

0.75mm2 = 24/0.2

1.0mm2 = 32/0.2

1.5mm2 = 30/0.25

Automotive 12v cables to BS6862 (or EN equivalent) are

0.5mm2 = 7/0.3

1.0mm2 = 14/0.3

2mm2 = 28/0.3

Edited March 24, 2018 by Alan de Enfield

[Nightwatch]

Does it matter if the cable is slightly oversized?

[Sea Dog]

Just now, Nightwatch said:

Does it matter if the cable is slightly oversized?

No, if anything it's better - expense is the biggest factor in choosing smaller csa cable.

(Thought you'd got fed up of thus thread and wandered off NW!)

[Nightwatch]

Just now, Sea Dog said:

No, if anything it's better - expense is the biggest factor in choosing smaller csa cable.

(Thought you'd got fed up of thus thread and wandered off NW!)

I need so little in length of cable, that cost is almost irrelevant. 

Im not fed up with it,  my manager got me designing a bathroom. She'll want a telly in the bathroom next. (She won't get one!!!)

so many jobs, so little time.

[smileypete]

On 3/22/2018 at 12:21, Nightwatch said:

Hello. I have asked this before about a year ago and can't remember the advice nor can I find the thread.

i am moving the telly to a different position. Want to run cable from existing 12v socket to a new socket where the telly will be. By the time it has gone up the bulkhead and over doors and down to the new location it's going to be about 5 metres. 

What size cable would I need. Also, I asked, in a small hardware shop, for some 12v cable and was told they don't sell it. Is 12v cable Different to 240v cable! 

Thanks.

The rule of thumb for safe cable loading is "amps divided by three",  for voltage drop with 12V loads this will also allow up to 5 metres separation between batts and loads.

https://www.google.co.uk/search?q=site%3Acanalworld.net+"amps+divided+by+three" 

Edited March 24, 2018 by smileypete

[Tony Brooks]

3 hours ago, Alan de Enfield said:

'Domestic' flexible wires (to BS6500 or EN equivalent) are 

0.5mm2 = 16 strands, each strand 0.2mm diameter - written as 16/0.2

0.75mm2 = 24/0.2

1.0mm2 = 32/0.2

1.5mm2 = 30/0.25

Automotive 12v cables to BS6862 (or EN equivalent) are

0.5mm2 = 7/0.3

1.0mm2 = 14/0.3

2mm2 = 28/0.3

Trouble is Alan that many will not grasp the significance of your BS6862

I think the data you quote for automotive cables is for conventional PVC insulation, not thin wall and it seem to em ist ois getting more and more difficult to get hold of standard PVC.

The data for thin wall from  Vehicle Wiring Products gives

0.5 sq. mm CCSA cable as 16/0.20

1 sq. mm CCSA cable as 32/020

2 sq. mm CCSA cable as 28/0.30 (as you say)

The thinner but more numerous strands in the thinner sizes is, as I understand it, to bring its specification in line with other BS/EN requirements.

It looks as if there has been some harmonisation between domestic and 12V flex standards.

None of which goes far in helping the OP.

[W+T]

On 3/24/2018 at 08:43, Murflynn said:

pedant alert!! 

how do you measure cable in mm?  is it diameter, circumference or what?

either `or what` or length, obviously dur.

[Murflynn]

when I worked in the pipeline industry we used to define washers as very short pipes 

[WotEver]

7 hours ago, Murflynn said:

when I worked in the pipeline industry we used to define washers as very short pipes 

With very thick side walls. 

[Nightwatch]

Ordered from 12v planet 4mm2 cable. Couldn't find anywhere in Newbury that understood what I was on about. Maplins were clueless and the guy in charge smelt like he doesn't wear deodorant.

Just a note, everything has at least 30% off.