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cable sizing and voltage drop

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hi everyone,

First timer here on the HPA forum. I'm working my way through all of the videos in the wiring fundamentals course for the second time as there is so much good information in here and I want to fully understand it all to the best of my ability. I plan on re-wiring almost the entire electrical system of my project car (battery relocation, fusebox and relay panel relocation, interior lighting and acessories, lights, turn signals, horn, etc.) and not just the efi system. My question relates to the cable sizing video which seems to choose cable size based on the amperage a device consumes. I understand how to make this calculation. However, I am wondering if we also need to consider voltage drop in our calculations when choosing cable size? If so, how do you go about doing this?



Hi Daniel

Being automotive you won't see voltage drop in the short lengths if using good quality wire

Regards Ross

Hi Ross,

Thanks for getting back to me. Just to clarify, is voltage drop an issue in longer automotive circuits? I.e. A cable between the battery (at the rear of vehicle) and the starter motor?



I was wondering the same. Found this table which was rather informative.

** As Ross has suggested good quality wire will not be held to these same standards. A good illustration of that is this. 200amp at 50' is further than the table below allows.

Hi Brian,

Thanks for finding out this information. So based on the feedback I think this might be the two main points:

A) no need to consider voltage drop in automotive applications when selecting cable size if you are going to use good quality cable.

B) choose the correct cable size based on the current rating only and if possible get this rating at a specified length.

Thanks again for your help and let me know if I've missed something.



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