Wire Sizing Question

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Wire Sizing Question

Postby Strop » Mon Oct 26, 2015 7:28 am

Hi all,

12v system being discussed. I have read about voltage drop and have found a number of calculators to figure out what size wire I should be using to minimise this issue to acceptable levels. Not a issue there and I Understand AWG And mm sq sizing..

I am having a number of circuits for various devices and for some it is easy. A usb or acc plug have the appropriate size wire going all the way to them. With lights though they come with their little wires poking out and the wire for the run to the light is a larger gauge to avoid voltage drop. The science would tend to tell me that the same gauge wire should be used all the way to the light but I can't or don't want to access the lights board to replace the wiring.

So, should I shorten the wires from the light and join the heavier gauge wire as close as possible to the light.?

I don't know but I am just thinking that the cable loss in that last little bit will be so small not to worry about it.

Then you have the fuse issue. If you have multiple lights on the one circuit your cable run is bigger and your fuse size will be bigger due to that the multiples of lights and therefore isn't that lighter piece of wire you join the heavier gauge cable to the weak point - not the fuse? For example , my hatch lights - 4 of- are only .5 amps each. I am going to run a ingle wire from the fuse box to one and from that join across to the others. Thus minimises the wire run as opposed to running 4 separate sets of wires from the fuse box. The wire for the run is much heavier and I will be using a 3 amp fuse. It is possible to switch all of these lights individually as well as a group. If. I wired each light individually I would be using a 1 amp fuse.

So if I am using only 1 light with the 3 amp fuse does the wire of the light become the weak point and a hazard.

I have to be honest and say that common sense is saying to me it is not an issue but the mad scientist in me is craving an answer..

The same goes for switches. Heavier gauge wire to the switch and then lighter gauge wire after the switch as the lights supplied wire will reach the switch.

Just askin?

Laurie
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Re: Wire Sizing Question

Postby Jim.Johnson » Mon Oct 26, 2015 8:13 am

Go with your common sense. The short run of smaller wire is no problem. It will still handle a lot more than the fuse and voltage drop at that point in the circuit is insignificant.
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