Wiring fog lights for power with relays/ where to fuse?

[GT_80]

Typically when I run fog lights or driving lights, I fuse the power going into the relay (30 pin on relay) and nothing else. Since I know the switches only see like 2-3 amps I never really bothered fusing them, and I always use heavy duty 120V metal toggle switches, I have never had a switch burn out. What do you guys recommend? I have seen wiring diagrams that have a fuse in the switch power only, or in both the switch power and relay power. I kind of like that approach, but don't want to check 12 fuses if anything stops working. I have a Buss 6 spot fuse holder for the power to the relays and I run a 10 gauge wire to that from the BAT+ junction box between the battery and the main fuse panel.

These are some popular diagrams I found:

Fusing both the Switch power and the relay power

fusing only the 30 pin on the relay (I'm not using an indicator light as in this example and realistically, you would want the indicator to light up off the relay to tell if the system really works)


The other option I have seen is without a relay, putting a fuse inline bwteen battery power and switch input, then outputting power to the lights directly. I have burned many lighted switches using this method because too much current goes through the switch. I always use relays now, even if I wire backup lights to my existing system - the Backup light wire trips the relay in that case.

 

[enoniam]

I believe it's more important to fuse the wiring going to the switch because if you develop a short to ground in that hot wire you are probably running a higher gauge (smaller diameter) wire to the switch which will be even less capable of handling the short than the wires running to your lights.  You may also be running the wire handling less current in a tight space, under carpet, etc which trap heat and/or be some kindling for your bonfire/truck.

 

[ygmn]

All wires should be protected by fuses or circuit breaker to prevent wire fromcatching fire whould it short out.

that is what fuses are for.... not to prolong life of switches.

 

[GT_80]

All wires should be protected by fuses or circuit breaker to prevent wire fromcatching fire whould it short out.

that is what fuses are for.... not to prolong life of switches.

Do you think I should fuse each individual switch power or could I use like 1 15A fuse and daisychain power to all the 6 switches off that?

 

[enoniam]

Do you think I should fuse each individual switch power or could I use like 1 15A fuse and daisychain power to all the 6 switches off that?

I'd do something like that.  Just make sure the wiring you use can take whatever the fuse is rated for.  If you get a short with enough resistance on one line such that it draws just under 15 amps and not popping the fuse you don't want it to catch on fire.

 

[ygmn]

the fuse/CB protects an entire circuit

You have a relay so:
you have to protect the high power side for lights
And have to protect the low power side that switches the relay on/off

Wire minimum size is based on the protection amp rating and their is a chart in NFPA NEC electric code for this based on wire type. but you can always use a fuse rated for less then what a wire can carry but NEVER the other way around. 

The fuse/CB is what has to blow/trip when circuit current reaches limit so wire does not get HOT and catch fire.

When you tap into existing circuits you have to be careful since you are adding to the circuit load and you could blow fuses when everything is running.

If unsure this is when you go to the Battery or a Positive bus Bar connected to battery.

Only cables not truly protected on vehicles are the battery leads and this is usually what can cause an electrical fire when a starter or starter solenoid shorts out.

Some power leads are designed to burn up and open the circuit these are called fusible links.

yeah I can get geeky.

 

[Zef_66]

I agree that all power wire runs should be fused to protect the wire. Nothing else. And the fuse should be less than the rating of the wire.

So if you are running a power wire to two different places, fuse both wires. And fuse them as close to the main power supply as possible.

Again, fuses protect wiring.

 

[GT_80]

That is pretty much the same conclusion I have come to- I have just never fused a switch before because the current is so low. I am trying to get better at wiring with every new vehicle I buy. My plans are to pull the power for the switches and the fuse block off the off the + connection point between the alternator and underhood fuse block. Each pair of 55 w lights draws about 9 amps, so theoretically if they are all on at once (which would be rare) I would be drawing about 54 amps max from the system, which is less than most car stereos with amps. I do not plan on putting subs in this truck, as I stuck them in my cutlass because that needed a compete stereo.

What I will try for a 1st go-round (and probably will leave it) will be to pull one fused 14 gauge wire from the + connection to the switches and jumper all the power to the switches together like this