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# Mil Spec Wiring - Question of wire size

### Tech Articles

Discussion and questions related to the course Motorsport Wiring Fundamentals

Hello,

I am currently doing a mil spec wiring for a car and I'd like to know what size should the wires be from:

1) Relay to Fuel Pump (044 bosch)

2) Relay to Electric fan

3) Relay to Wiper motor

4) Relay to the lights

Thanks

the very short (and half accurate) answer:

Thank you for the reply Ludo, the distance from relay to fuel pump/ wipers/ lights etc is about 6-7 feet and I was thinking of using 16awg mil spec tefzel wire. From your experience would that be ok? What if I run 2 x 16awg for each output? Or do I need to consider a higher awg wire?

additionally, i'm assuming there's a formula to determining multiple wires of smaller gauge vs a single wire of bigger gauge. would anyone have any insight into this? I found this link below, but it only states the answer based on the input calculator, and not the formula..

http://www.wirebarn.com/Wire-Calculator_ep_42.html

Mitch, the formula is the same than the resistors in parallel.

or, when it's the same wire size Rt= R/n ("n" being the number of wires)

(look at the link I posted above for the actual values.)

Two 16awg wires, 15.8Ω/km each -> 15.8/2 = 7.9 -> 7.9Ω/km

So ≈ one 14awg (10Ω/km) since 13awg doesn't exist

chrisqy, two 16awg should do it for one 044 pump (personally I still would use one 12awg wire)

For the rest, you have to look at the actual current draw.

thank you, that was exactly what I wanted to know

I have always compared wire sizes in terms of cross-sectional area. Maybe that is not correct as I have heard that most current travels along the outside of the wire?

Gustave

Apologies for the zombie revival, but Gustave seems to have been mis-informed.

Extremely high frequencies seem to act that way, but when I say extremely it's well into what would be radio frequencies - megahertz, through gigahertz, and above - and the wire acts more as a wave guide.

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