Cat5/6 for relay activation?

**92 Green YJ** · 02-05-2010, 04:23 PM

Hey guys. So i've been getting some conflicting feedback on this idea. I've seen it mentioned here in a few posts but nothing solid. So heres what I want to do. I just made a new switch panel and I am trying to clean up some of my wiring. I had a spare 10ft Cat 6 cable laying around and for the heck of it I cut the end off and removed about 6 inches of the outer sheathing. Inside the cable is 8 seperate wires. 24 gauge I believe. They are stranded wires, not solid. What I am wondering is if I can use this to activate my relays with. I know that the power to activate a relay is pretty low draw. Will this wire be able to handle that though? Or am I asking for problems? 8 wires is perfect for what I need and it would be great to just have it all inside the one cable between my switch panel and my relays. I'm thinking the run wouldn't be more than 5 feet. So what does everyone think?

CO64CJ5 · 02-05-2010, 07:20 PM

Go for it. They'll handle the relay coil current with no problem. However, if you're running power on one wire to possibly actuate 7 relays, you might want to do some calculations. My main concern would be that the wires be stranded, but you've confirmed that they are.

A second concern would be for the durability of the insulation, but this can be addressed by careful routing and using wire loom and grommets where appropriate. Be sure to secure the cable's jacket at each end to avoid strain on the wires. Depending on where you're mounting your switch panel, it might also be judicious to enclose the back of it to protect the wires from damage.

Also probably best to avoid pinching the cable, and tight-radius bends.

**5-90** · 02-05-2010, 08:26 PM

Cat 5/5e/6 is four pair of 24AWG wire - typically solid.

Trip current for a DIN relay is 100-150mA - data signals use current in that range, so the data cable will be no trouble.

However, as noted, 24AWG solid is awfully fragile. Avoid sharp bends (allow 2" or more inside radius,) avoid "mechanical interference" (anything that can rub on or whack the cable,) and allow room for movement.

I've seen patch cables that use stranded twisted pair (same thing - but the 24AWG wires are made using something like 40AWG strands instead, so they're more flexible and a bit more tolerant) but they can be difficult to find.

You can also use things like serial cables or printer cables - they're much the same, but they're not set up as a "twisted pair" configuration (normally - the TP is to prevent crosstalk between pairs,) and they're stranded a bit more often than the UTP (Unshielded Twisted Pair) that you're currently planning on using. Just a thought...

**rivalarrival** · 02-05-2010, 09:28 PM

American Wire Gauge table and AWG Electrical Current Load Limits with skin depth frequencies

If I'm reading this correctly, 24awg wires are rated to carry 3.5 Amps. A typical 30-amp automotive relay's coil draws 160mA. So, for current draw, you should be A-OK. I would make sure that you use a 3.5-Amp or smaller fuse on those circuits - connecting it directly to an accessory circuit, you can potentially draw up to that circuit's fuse rating (usually over 15 amps) which may be enough to start a fire.

Cat5/Cat6 is pretty sturdy stuff. As long as it's not moving around too much, you should be fine, especially with stranded wires.

**92 Green YJ** · 02-08-2010, 08:01 PM

well I guess theres really only one way to find out. But you guys definitely re-assured me quite a bit so I'm gonna go for it and see what happens

Slithering_Joe · 02-08-2010, 08:26 PM

My concern would be if the CAT5/CAT6 cable can take the vibration. Also, if it is in the engine compartment, can the insulation take the heat cycles and oil & gasoline vapors.

PhulesAu · 02-09-2010, 06:05 AM

Isn't that stuff pretty much rated for indoor and Airconditioning.??

**SirGCal** · 02-09-2010, 07:56 AM

And automotive relay can consume as much as 700mA to trip depending on the situation. Still within the wire's capabilities but, one wire per relay only, no grouping them up. They will also NOT handle the heat so you have to keep them away from the engine, exhaust, etc. Their insulation isn't element rated as automotive wire can be.

If the cable is Plenum grade (CMP) then it will have a fire retardant in the plastic sheeting. But that still won't protect against direct heat. It's made so that it doesn't accelerate a fire in the attic or something of that nature. Riser (CMR) also has some fire protection but again, not against direct heat sources. It is less protected than Plenum grade. General wire you use inside for example, has no protection.

**92 Green YJ** · 02-10-2010, 09:23 PM

well I went ahead and tried it. Only gotten the first 2 relays hooked up so far. I've been up to my neck in wiring for 2 days solid. Basically ripping out ALL of my accessorie wiring and some of the factory wiring that I never or no longer need. Got the new switch panel installed finally. Hooked up the fuel pump relay and the On Board air relay so far. Flipped the switch and the relays activated just fine. left the OBA one on for a few minutes and touched the wire. It wasn't even hot. So I think i'm good to go

**rivalarrival** · 02-10-2010, 09:33 PM

Quote:

Originally Posted by 92 Green YJ

well I went ahead and tried it. Only gotten the first 2 relays hooked up so far. I've been up to my neck in wiring for 2 days solid. Basically ripping out ALL of my accessorie wiring and some of the factory wiring that I never or no longer need. Got the new switch panel installed finally. Hooked up the fuel pump relay and the On Board air relay so far. Flipped the switch and the relays activated just fine. left the OBA one on for a few minutes and touched the wire. It wasn't even hot. So I think i'm good to go

Great! If you're excessively paranoid, you could check the current with a multimeter on set on DC amps.

Just make sure you're using good engineering practice and fuse your circuits such that no more than 3.5 amps can be pulled through any wire before the fuse blows. Better to do it now than risk an electrical fire a few years down the road.

**5-90** · 02-10-2010, 10:28 PM

Quote:

Originally Posted by 92 Green YJ

well I went ahead and tried it. Only gotten the first 2 relays hooked up so far. I've been up to my neck in wiring for 2 days solid. Basically ripping out ALL of my accessorie wiring and some of the factory wiring that I never or no longer need. Got the new switch panel installed finally. Hooked up the fuel pump relay and the On Board air relay so far. Flipped the switch and the relays activated just fine. left the OBA one on for a few minutes and touched the wire. It wasn't even hot. So I think i'm good to go

Told you.

If you want to fuse the circuits, don't even go with 3.5A - recall you're dealing with 24-28AWG here. Fuse to 250-500mA, tops.

**rivalarrival** · 02-10-2010, 11:59 PM

Quote:

Originally Posted by 5-90

Told you.

If you want to fuse the circuits, don't even go with 3.5A - recall you're dealing with 24-28AWG here. Fuse to 250-500mA, tops.

24AWG is rated to 3.5 amp continuous. But yes, fusing to the minimum necessary is a good idea.

CO64CJ5 · 02-11-2010, 06:19 AM

Just be careful how you define minimum. You should allow for the possibility that you will activate all the relays at once. A couple of amps should be sufficient -- you don't want the fuse to blow when you flip the last switch . . .

If you're concerned about "inrush" current, you could use a slow-blow fuse.

**Phreak480** · 02-11-2010, 08:16 AM

I've used cat 5 to feed relays on a few vehicles over the years without issue. it sure is convenient to have all the wires bundles together. I use some heavier wire to feed all the switches and then the wiring in the cat 5 goes from the switch to the relay.

**92 Green YJ** · 02-12-2010, 01:29 AM

so you guys are suggesting I fuse the cat 6 wires from the switch to the relay?? one of the ideas behind this re-wiring mess was to remove some of my add on fuse blocks (was up to 4. the biggest Blue Seas I could find, a pair of 4 fuse blocks and a six fuse block) had fuses on every switch, every relay, and a few other things. Now i'm running all of my switches off one fuse.

edit, all the relays are of course on their own fuses as well