electric cable rating

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wickford90

wickford90

Well-Known Member
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wickford essex
Just been reading cowasaki excellent sticky on electrics, too find how to rate cable, still none the wiser a bit over my head at the moment. Need to wire an electric fan instead of viscous its a 12v motor and 120 W what is the calculation to work out correct wire size / rating.
 
Basically Current = watts divided by volts (120/12 = 10 amps). That will be the normal operating current, probably worth giving it about 50% extra so you are looking at about 15 Amp rated wire. These calculations are close enough, reality is that you will be looking at about 13.5v with engine running but 15A cable will still be fine.
 
Kwakerman said:
Basically Current = watts divided by volts (120/12 = 10 amps). That will be the normal operating current, probably worth giving it about 50% extra so you are looking at about 15 Amp rated wire. These calculations are close enough, reality is that you will be looking at about 13.5v with engine running but 15A cable will still be fine.
Click to expand...

Thats the calc I was looking for, duly noted and filed away. thanks
 
Another consideration is the volt drop in the cable due to its internal resistance.

If you are passing 10A, then look at the next cable size up to minimise losses in the cable.

To run a cooling fan I'd be looking at something like 2.5sq mm. 1.5sq mm will do the job but 2.5sq mm would be better.

Peter
 
Thanks for all that, one other query, the fan will obviously cut in and out as needed but i want an on / off switch so i can turn it on/off, as I use it off road and tow.Would i need to run 2 or 3 wires to a 3 way on/off/normal switch.
 
Not sure of your system but easiest/basic to use will probably be the 'three way' option on/off/on (i.e. when the switch is in the middle position none of the contacts are made). Feed the supply (fused of course) to the middle contact, from the 'end' contacts connect one wire direct to the fan +ve (permanent on) and the other end of the switch to the fan temperature switch power feed (auto setting). If you do it this way then the switch needs to be rated to match the wire and fuse (at a minimum). If the system you buy uses relays or some form of intelligent switcher then the above is probably redundant and you need to go by supplied instructions.
 
Kwakerman said:
Not sure of your system but easiest/basic to use will probably be the 'three way' option on/off/on (i.e. when the switch is in the middle position none of the contacts are made). Feed the supply (fused of course) to the middle contact, from the 'end' contacts connect one wire direct to the fan +ve (permanent on) and the other end of the switch to the fan temperature switch power feed (auto setting). If you do it this way then the switch needs to be rated to match the wire and fuse (at a minimum). If the system you buy uses relays or some form of intelligent switcher then the above is probably redundant and you need to go by supplied instructions.
Click to expand...

I have an on off on switch spare, so maybe safer to see what wiring diagrams come with the fan, thought i could save a bit of time running cables before it arrived. thanks
 
I've been doing a similar bit of wiring and everything was listed in gauges.... afaik gauge is amps less a bit for a safety margin unless anyone has a correct technical conversion.. ie 18 gauge means u need 15 amp for a safe bet??

cheers steve
 
ebbadger said:
I've been doing a similar bit of wiring and everything was listed in gauges.... afaik gauge is amps less a bit for a safety margin unless anyone has a correct technical conversion.. ie 18 gauge means u need 15 amp for a safe bet??

cheers steve
Click to expand...

That won't work on all occasions as gauge number goes down as diameter increases i.e 8 gauge is heavier than 16 but not as large as 4.
 
It's not difficult. Just go to vwp wiring. Look up thin wall cable and get the size that will do the required current ( Amps). Try and get the correct colour code too.
 
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