Re: what is a relay?

Posted by txblu on November 15, 2004 at 12:03:15 from (199.46.199.230):

In Reply to: Re: what is a relay? posted by StuBC on November 15, 2004 at 07:08:10:

Last tractor lights (JD and Ford) I bought were 12v 35 watt. Watts = V/Amps. So that's right at 3 amps each x 4 lights is 12 amps. 12 amps is ok for 14 awg and a 15 amp fuse is usually used for 14.

But the whole amperage thing is about wiring insulation. The current that a wire will safely carry is based on the insulation. Just looked up Fusing current for 14 AWG wire. It's 166 amps....not a misprint, 166 amps. Fusing current is the current that melts the wire.

So you can see 15 is a long way from it. If you have a conductor inside a small pipe with a lot of other wires and have soft plastic insulation it is a lot different deal than having one single wire strung out in air with heavy plastic insulation.

Do this. Put in the fuse at 15 amperes. If it blows, you can either put in a slow blow 15. Or if your wiring is as usual on a tractror, go ahead and put in a 20 ampere. Iffin you get an overload that is that bad, you'll probably smell the insulation getting hot before you melt it to the point where you have a melted wiring harness.

For most plastic insulation that is available at the auto store 85 F rating should easily carry 20 amperes in an overload.

Besides if something shorts and overloads the circuit but isn't quite 20 apmeres, you are going to notice something is wrong and go investigate. So it won't be overloaded all that long anyway.

But if you are really concerned go rewire with either 2 14 amp ckts @15 amps or use 12 AWG wire and the 20 amp fuse.

Mark

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