I'm adding another fuse/relay box to my truck. Here is how I plan it and anybody who knows wiring please chime in if you think anything is wrong. I am using relays with a built in fuse already so there is no need to fuse the main power cable. The main ground/power cable will be 6AWG and go into either a breaker or fuse then go from 6AWG to 14AWG too the relay/fuses. Total length 2-3ft. The ground wire will follow the exact same except no fuse/breaker. The trigger wires will be 18AWG and will only get fused if I don't tap into an already fused wire. The wire going to the device will probably be 18AWG. Sound good so far? Now my only question is what size should the breaker/fuse be for the main power cable? As I said it will go from 6AWG down to 12 14AWG wires crimped to the 6AWG wire.

 

breaker/fuse should only be as big as the draw on the whole box. 6awg can take some current, especially that short of a piece - so I'd count up the draw on each downdraft circuit.

 

He will want some overhead in that fuse otherwise any little spike can blow it. If he's running any circuits that turn on and off he will see spikes.

 

Exactly so I went a little bigger. Also according to the calculators I'm finding to combine 6 14awg wires it equals 6awg

 

What is the relay fuse rating? The wire gauge is only half of the equation. Primary wiring (to power the relay) and secondary wiring(to power the load) need to be known. I imagine this is being used for small amp items. ??? Relays use small gauge wire because they only draw a small amount to power them.

 

It takes and mini fuse they are 40AMP relays. The trigger wire will probably be 18 gauge, ground and power 14 gauge, and the device will will depend on the device. It will power to big items. One an air compressor for my rear air bags an train horn and the other will power my locker selenoids (2)

 

This chart will help you with the right gauge wire for the length(secondary wiring). The coil wire (primary) on small relays such as used for the fuel pump & ASD(in the second gens) are probably less than an amp so 18-14 is plenty.

https://www.engineeringtoolbox.com/a...uge-d_730.html

 

Thanks for the link!

 

A main feed line and it's protection breaker or fuse can often be quite a bit smaller than the total sum of the rated protection for all the circuits in the panel since it's usually a safe assumption that it isn't common or even likely for all the circuits to be drawing full load current simultaneously.

For example , I'm just doing my own aftermarket fuse/relay box install, and my cheapo aftermarket fuse/relay box has 5 of those bosch 30A relay socket and this bigger ~50 amp relay socket, all with their own fuses. Even though it's only like two feet, the 8 gauge positive feed wire I'm using is getting an inline 60A fuse/fuse holder, I am just planning on using all 10awg power bus wire, appropriately fanned out from the feed line, all throughout the inside of the fuse box.and fused accordingly. Though my box could technically handle a draw of nearly 200A per the rating of the sum of all its circuits, that will never happen in the real world. Since my planned loads are things like radiator cooling fans, air compressor clutch, accessory lighting, possibly headlights , etc That stuff is never all going to come on all at once. And if it did I's presumable still be nowhere nerar the 200A mark. ie my air compressor clutch probably will likely draw well under 10 amps, my e'fans probably draw somewhere around 10A each. I am betting I'll never blow the 60A fuse. If I do, I may have to upgrade feedlines and get a bigger fuse.

It's probably **** overkill but it's what I'm doing.

 

I don't know what I'm going to do about the power feed wire and grounds. I'm trying not to use a bussbar