What Size Cable?

[emandvee44]

I need to run a cable to supply a new 12v supply appliance on board. How do I work out the size, 1.5mm2 or 2.5mm2? The appliance has a cigarette lighter type plug.

Cheers,

Michael.

 

[CLB]

Depends on how much current the appliance draws and how far away from the power source it is.

 

[emandvee44]

5.0m cable run, appliance uses 0.665 kwh/24h if that makes any sense?

M.

 

[pagoda]

5.0m cable run, appliance uses 0.665 kwh/24h if that makes any sense?

M.

That appears to translate to about 28W or roughly 2.25A at battery voltage. It's not that much but 2.5mm2 should cover it nicely without terrible loses. Probably worth using tinned cable since any corrosion will add losses to the cable run.....

 

[emandvee44]

Thanks, I will look for two core 2.5mm2 - not so easy to find in B&Q type shops.

M.

 

[matthewriches]

If you are limited to B&Q or Homebase diy style places then you'll be looking for heavy duty extension leads marked as 2.5mm. These will be 3 core but you'll just use 2.

If you can, best bet is to buy online!

Thanks, I will look for two core 2.5mm2 - not so easy to find in B&Q type shops.

M.

 

[VicS]

Thanks, I will look for two core 2.5mm2 - not so easy to find in B&Q type shops.

M.

If it is only 28 watts then that is only just a bit more than 2.3 amps at 12 volts. You wont need anything as heavy as 2.5mm². That's 25 amp cable!

1.25 mm² (domestic 13 amp) will be adequate for a 5m run. You should find that easily enough although you don't really need 240 volt rated cable.



BUT BUT BUT

What is this appliance. If it is somtihing that only runs intermittently then then it will take more 2.3 amps while it is running

What is it ? Whatis is max current draw in amps

Its amps while it is running we need to know Not how much power it uses over a 24 hour period!

 

[KenMcCulloch]

As an electrical numpty, more or less, currently (geddit?) doing some boat electrical upgrading, I have found the Blue Sea Systems phone app Circuit Wizard invaluable. Easy to use and only very basic electrical knowledge is required.

 

[colind3782]

Two core flex is readily available online.

https://www.ebay.co.uk/itm/2-3-4-CO...hash=item41d3664524:m:mIFKfQv-XBdE6OPawlfy8MQ

 

[PuffTheMagicDragon]

Given the short lengths required I would go for the 2,5mm² anyway, even if they might be over-kill. As VicS rightly pointed out, the important factor to be considered is the maximum current at any time and not the 24-hour average. Personally I prefer separate wires to twin cable because they allow for more ventilation (cooling in case of occasional over-heating) but that is just my way of looking at things.

 

[emandvee44]

It is a portable fridge freezer CFX40W
M.

 

[Richard10002]

DC rating is 7A, whatever that means. As a fridge, it wont, (shouldnt), run 24/7, so the max amps drawn when running, wont be the average amps drawn over 24 hours.

My Waeco Fixed 40l fridge seems to draw about 4 or 5A when the compressor is running, so I would budget for a cable that can cope with the rated 7A, (perhaps 10A to be on the safe side), and, perhaps more important, a voltage drop of less than 3%. With your 5m run, I'd go for 6mm cable.

 

[VicS]

It is a portable fridge freezer CFX40W
M.

It is rated at 7 amps, as Richard observes. The manual tells you this current rating in the technical data section

7 amps is therefore the current to be taken into account when determining the cable size

For a 5 metre cable run you will need 4.5mm² to stay within a 3% volts drop.

3 mm² would have been Ok for a slightly shorter cable run of about 4.5 m

6 mm² would be generous

 

[Richard10002]

6 mm² would be generous

Agreed

 

[MikeCC]

But whatever you buy, don't get domestic solid core cable, hence the earlier suggestion of flex type.

 

[PaulRainbow]

Wonder how you get to neatly fit a pair of 6mm cables to a fag lighter socket

It's a fridge, not a windlass, let's not get carried away with voltage loss calcs. 2.5mm over 5m is a 4% loss, the fridge has a low voltage cut out of just 10.1v, 2.5mm cable is fine for this purpose.

For wiring to a socket, some round flex is tidy, such as :

https://www.amazon.co.uk/Black-Rubber-Flexible-Cable-2-core/dp/B0051ODXCW

 

[emandvee44]

Thank you for the advice. I purchased a 20amp rated cig. Type socket and when I return to the boat next week I will measure the cable run accurately. Could be shorter possibly than my original estimate.
M.

 

[VicS]

Wonder how you get to neatly fit a pair of 6mm cables to a fag lighter socket

It's a fridge, not a windlass, let's not get carried away with voltage loss calcs. 2.5mm over 5m is a 4% loss, the fridge has a low voltage cut out of just 10.1v, 2.5mm cable is fine for this purpose.

For wiring to a socket, some round flex is tidy, such as :

https://www.amazon.co.uk/Black-Rubber-Flexible-Cable-2-core/dp/B0051ODXCW

You can't ( whoops, that looks bad if you leave out the apostrophe )

IMO a sensible way forward would be to run some heavy cables to a junction box local to the Coolfreeze's intended location and to connect the socket close to this using lighter cable. The same size as the supplied lead perhaps.

Cigar lighter sockets are often likely to make poor contact so it would be better to do use an alternative on the boat. The whole installation would have to be fused at 10 amps if the supplied fused plug is not used.

I guess the Op will also want to run the Coolfreeze in the car so the existing cable and plug would have to be retained for that purpose.

 

[mersey]

If you're installing a cig lighter socket the cable should be rated to the highest amp age cig lighter device, or what the socket is rated to.

Otherwise someone might come along at some point, maybe a subsequent owner, and plug something else in, that the cable cannot then handle.

 

[VicS]

If you're installing a cig lighter socket the cable should be rated to the highest amp age cig lighter device, or what the socket is rated to.

Otherwise someone might come along at some point, maybe a subsequent owner, and plug something else in, that the cable cannot then handle.

The circuit should be appropriately fused .