Proper way to wire additional circuits?

[Jimmy P]

Let me start by saying I've been unable to find what I'm looking for in my searches, so if you can point me in the right direction, please feel free.

I've spent a good bit of the past couple of weeks cleaning up the wiring harness on my Jeep after some rodents made a meal of a good piece of it. While doing that, I also ran into and cleaned up a lot of the hack work I've done over the years. I chalk that up to being young and dumb. Now I'm older and not as dumb, I want to try and do things a little closer to correct.

In my plan, I've got a series of auxiliary circuits I want to run, including additional switched lights, comms, charging ports, and prepping for a fridge that I don't have now. Apparently I keep confusing myself, and I'm hoping someone can shed some light on things for me.

My initial assumption was that I'd run two additional fuse blocks, connected to the battery via 100 amp breakers, with properly sized leads. The fuse blocks I'm looking at have a negative buss, the idea being I can have a good ground location and wire each of the circuits to block for both positive and negative and removing most of the oops factor of a bad ground.

Question 1 - Am I correct in that if I want this to be keyed / switched hot, I'll need a 100 amp relay between the battery and the breaker?

Once I have the additional fuse blocks in, I'm relatively certain that I can wire the simple circuits with the appropriate wire and fuse easy enough. My real confusion here is for the switched lights, and the possible (probable?) use of relays.

1st, if I am assuming a 20 amp circuit for a set of lights and I have a 20 amp switch, isn't is feasible that I could run the power from the new fuse block to the 20 amp switch and directly to the light? If that's the case, why is it that relays are almost universally recommended? Is it because many switches can't handle 20 amps, so it's better safe than sorry? This is truly for my edification. I already have relays, so it's not a matter of going cheap.

2nd, if I wire the aforementioned lights as fuse block to switch, switch to relay, relay to light, where does the relay main power get connected to? I understand it should be a fused source, but I'm not positive I can use a 2nd circuit from the same fuse block, or if I need an inline fuse and go directly to the battery or some other distribution panel. Logically, I believe I should be able to use a 2nd circuit in the fuse block, but I've read some pretty conflicting stuff lately, and I don't want to do this wrong. Specifically, I read that both circuits going to the same source (the fuse block) is a disaster waiting to happen. It's illogical to me, but I'm no electrical genius.

Any insight would be greatly appreciated!

 

[Jimmy P]

Okay, I think actually sitting down and trying to draw it out helped. If my logic and understanding is correct, this is how I should be wiring it, assuming I need the relay. Does it seem right? Also, any thoughts on the actual need of the relay? The lights I have at the moment are 27 watt LEDs, and it seems as though they'd require a 3 amp circuit each (6 amps for the pair) so a 20 AMP circuit should be sufficient. Maybe I'm over thinking this. Maybe a sanity break is in order

 

[The other Sean]

One thing to consider with using relays is you can keep the length of the power wires down. Add in the distance from the feed line, up in to the cab and back down. The added resistance adds up and can reduce the power to the light or accessory. Also, you can run smaller wire to the switch, so routing wires up in to the cab is easier.

Another thing I have found helps me is to draw things out and also only focus on ONE wire or ONE circuit at a time. It's easy to lean back and only see ALL of the wires and your brain shuts off.

 

[W4P]

Yes key is wire! Heavy wire from device to relay to battery. Heavy wire costs,harder to run so need less. Relay control lines can be light, bundled easier to run ,Trace. Check out premade kit on eBay which uses http://www.ebay.com/itm/Universal-Waterproof-Fuse-Box-Relay-Panel-distribution-Cooper-Bussmann-Off-Road-/222622568463. Bussman is popular. Check out YouTube videos you can build one. Of course spod system for high end. Good luck. Read lots and yes draw lots!!

Sent from my Nexus 7 using Tapatalk

 

[aearles]

Exactly. With a single small load (like 6A) the relay is kind of pointless because the size wire you're running to the load can be small. But if you're installing a few switches with a bundle of control wires back to near the fuse block, then a pack of relays probably makes sense and would make things cleaner and more flexible for the future (like an sPOD).

Also, you should size your wires and fuse appropriately for the load. For instance, a 20A fuse is not appropriate for a 6A load, especially if using small gauge wire.

 

[Jimmy P]

Thanks, guys! I really appreciate the info, I definitely have an understanding surrounding the fuse being relational to the wiring. I hadn't thought about the wiring size being a factor when putting the switch panel in the cab. That's a great point. Drawing, drawing, and more drawing is in order. I'll be doing quite a bit of "bench racing" as I tailor the plan.