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Wire Size vs Amp Rating

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hey guys, had a rep come by the shop recently and had some wire which he says is much smaller then other brands (he directly compared to Narva) but still have the same current rating...

Ie Narva 4mm Diameter wire is rated to 15amps and he says his 1mm wire is rated to the same amps... He is from a reputable company and the stuff isnt cheap so was curious...

I didnt think you could change the amp ratings of cable of a given diameter unless it was made of another material?

Are you talking about insulation OD ? 15amp in a 1mm OD, I don't think so... 15amp in a 1mm² conductor (~17awg), maybe.

Like already discussed in another topic, Amp rating takes many parameters into account.

The main thing is the melting point of the insulation. the more amp you put into the wire, the more it will heat.

Narva use PVC insulation so is have very low melting point (generally speaking, it start to melt above 80°C) and it very bulky; the "4mm" is only 1.85mm² so a bit under 14awg (14awg = 2mm²).

In comparison, a "Mil spec" wire (Tefzel Insulation) in 14 awg will only measure 2.2mm OD and can take more than 30 amps simply because it insulation is rated at 150°C (it melt way above that).

But, the amp rating is only one factor. 15amp in an 20awg (0.5mm², 1.3mm OD), the wire would survive, but you will have such a big drop in voltage due to the resistance that it would be virtually unusable... (plus it would get really hot)

Take a look at this:


Voltage Drop Calculator

Hey guys,

sorry for answering to this old thread, but I wanted to see at the 44A0111-current pdf which is linked to here.

This pdf seems to have dissapeared from the forum? Someone has a version if this?

Thanks Andre!

Nice graph showing the temperature factor in this equation.

I have a Cosworth IPS32 which has most of its high Amp outputs, meaning 25A on 16AWG pins/wires.

If using the full 25A cont. on that spec44 or spec55 (in my case) wire it would get way to hot (+70C)

Seems like 12A per pin is about the most I should probably use?

What am I missing here...


If you have a load pulling cont. 25A from one size 16 pin then you'd be well advised to split the load across 2 pins, 12.5A each. Don't run 25A through a single size 16 pin/wire.

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