I was reading a article the other day that showed a picture of the owners car interior , It showed a large group of relays nicely wired by the floor shifter. I always thought that the relay should be placed close to the device that it was to activate. Whats the general consensus on this.

My Duster is currently that way with a Painless fuse/relay panel. My Mirada, which I wired, had the relays close to a power point and device being operated. Fuel pump relay was in the trunk close to the battery and pump. Had a dedicated B+ under the dash, and another under the hood. Rad fan and water pump relays were under the hood on the fenderwell. Was clean and all relays could be triggered with a simple small gauge ground wire to a switch panel. Downside they tell me is that "if" you wreck, you could possibly short out that ground circuit (like the fuel pump) and it will turn on and keep running despite what you do with the switch until someone hits the master kill.

The only purpose of a relay is to lighten the load on the control circuit and shorten the distance of power to the item being controlled. Though some of these pre-built panels look zoomy they don't do the job as intended. Why would anyone run battery power to a relay in the driver compartment and back to the fuel pump which is with in a few inches of the battery? Makes no sense what so ever to me. All my relays are less than 12" fro the device they control.
Doug

You need a light wire to trigger the relay and a heavy wire to carry power from the relay to the device. Seems only logical to put the relay close to the device.

If you have 10' of #12 wire total in a circuit it does not matter if the relay is at 1' or 9' the voltage drop will be the same.

The key is to reduce the total wire length while keeping the relays and overcurrent protection in a serviceable location where it will not be damaged

A relay is just a electrically operated switch. They are not magic devices that fix everything. Sorry if this sounds like a rant, but I see guys make a lot of basic wiring mistakes.

most wiring problems are incorrect wire gauge for load or length and not using relays that can handle the load.

Judging from new cars and aircraft, it seems that the relays are located in a place that's convenient to group them rather than the distance to source/load.

Whats nice about this also, Is you can easily supply Big power to one place, to multiple relays and send the current out with correct size wiring to its components and signal them with low amp switches.


But also see the advantage of putting a relay in the back near the bat/fuel pump in that situation. IMO, both can be used together to work best for your electrical system.


EDIT, just what he said; distance to source/load.

I do not agree with the voltage drop being the same. Acceptable maybe, but not the same per ohms law. That being said why use an extra length of heavier gauge wire than needed? Install the relay near the powered device with the proper gauge necessary to carry the required current.
Doug

Can you please explain?

I love the arc panel all the relays and connections in one spot. what's the difference if I put the relay near the water pump. you still have to run power to the relay.

If you place the same amount of current over a 1' run or a 10' run, the voltage at the end of the 10' run will be lower when using the same size wire.

The larger the wire, the less drop you will observe.

This is why all the relay kits I build use 12ga wire. Is it larger than maybe needed, possibly. Will the voltage drop be less than if using 12 or 16ga wire, you bet.

In the electrical scheme of things if you use the correct wire size for the amperage. 1 ft, vs 10 ft. is nothing. That's the point that was being made.

In the industry of electric your running lengths of a 100 ft plus for 20 amp and higher circuits.

In reality you can put a relay anywhere. Heck if a high enough amperage switch and heavy enough gauge wire is used a relay isn't even necessary. Just not the way I would do it. Mine has the relays by the pump (power from the battery direct) and on the motor plate (power picked up at the alternator).
Doug

https://youtu.be/vZL0tSnzK_4... I hope this helps...

Maybe just want to work...
https://youtu.be/vZL0tSnzK_4

In the original posters scenario, if you put all the relays inside by the shifter, you defeated the whole purpose of using a relay. The purpose of a relay is to reduce the number of heavy gauge connectors and shorten the length of heavy gauge wire, thus reducing voltage loss, plus simplifying the wiring, saving money and reducing weight. They ran the heavy gauge wires within reach of the driver. At that point, just skip the relay and use a 30 amp toggle switch.

I have an arc 8000 switch panel/relay board in the cab of my Dakota, and use the ARC relay to trigger another relay close to the source, fuel pump in the back, fan and water pump up front.... Everything else runs off the arc panel.

I run a Leash board up front with another 2 relay board at the back for the fuel pumps.

Less spaghetti if the relays are close to the device. If you have electric fan(s), a water pump and/or other high current components in the front of the car, a single heavy gauge wire ran to a junction or a harness providing high amp power to a group of relays is a cleaner set up. High current 12v can be routed to the individual components from the relays rather than running all of those heavy gauge wires from the interior of the car.

Same with the fuel pump(s). The relay is always near the pump.