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Wire Sizing with cumulative loads

EFI Wiring Fundamentals

Discussion and questions related to the course EFI Wiring Fundamentals

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Good day,

I am currently attempting to design a fairly simple circuit but can not figure out what the best practice for sizing the wire is;

For example lets say you have;

4 x Injectors each with a maximum draw of 2A at 13.8V DC.

Now the simple method is to simply calculate that you need 8A capacity for a given length of wire lets say 3m (or roughly 10 ft) with a 2% voltage drop. = You would end up needing a 14GA wire to safely supply these 4 injectors.

Now the real question is that these injectors will not be loaded at the max continuously at the same time. Is there a best practice to use in order to determine this, and can it be scaled to more complex wiring systems using various components on a circuit?

Thanks,

Jeff

Im only going to partially answer your question as the answer varies depending on what component you are driving...

For injector wiring I would make my calculation based on that maximum current being continuous. The reason being that it is very common to see injector duty cycles up near the 80% mark. Even though in many cases they wont be running at 80% for a long period of time it could still long enough to generate considerable heat and melt insulation if for instance you done your calcs based on 50% DC. Having said that, 14AWG sounds big for 4 x hi Z injectors. normally a 16 or 18awg will do 4 (im not calculating nothing here, just quoting what I typically do).

For things like direct spark ignition coils where even at redline they are rarely running at more than say 20%DC and there will unlikely ever be more than one charging at the same time then you can use wiring much reduced over the total maximum calculated current required for all 4 coils.