Cat 5 for relays?

[mk ute]

Quick question for all the experts, is cat 5 cable (the stuff normaly used for computer cableing) suitable to use for triggering relays? Reason being, i want to set up some relays in the rear of the ute (getting power from battery in the front), and be able to switch them from the cabin. I have a fair amount of cat 5 cable, and thought if suitable, it would save having multiple runs of cable under the ute.

Any feedback would be great.

[-Scott-]

For relay coils, yes, you should be OK, presuming you don't try to energise lots of relays from the one core.

[DamTriton]

Use trailer wire, usually available in 5 and 7 conductor versions, and cheap enough at Kmart.

The Cat 5 cable may be a bit on the thin side and may drop voltage enough under some circumstances to allow the relay to drop out, or heat up the cable enough to allow the conductors to short to the earth shield.

[-Scott-]

The Cat 5 cable may be a bit on the thin side and may drop voltage enough under some circumstances to allow the relay to drop out, or heat up the cable enough to allow the conductors to short to the earth shield.

Gary, you know how to do the sums. You should also know that most Cat 5 is UTP.

You're usually very good on these technical questions. What are you smoking this morning?

[drivesafe]

Hi mk ute, provided they are standard headlight type relays, as Scott posted, they will work fine and even with long runs, which I would be surprised if you would be using long enough runs in a vehicle, but with long runs, you will introduce some voltage drop but these relays work well even at 10V and only draw about 0.15 amps max.

If it’s a solenoid type then you need decent size cable like as DAMKIA suggested because solenoids pull anything from 0.6 amps and ironically, the better the quality of the solenoid, the higher the current requirements.

[GeeC]

I wouldn't do it.
The gauge is a little on the small side.
The insulation is a little on trhe thin side.
It is likely to be solid core, and will be prone to break where your connectors are.
Use the trailer wire mentioned or source some other flexible multicore cable.

[chimpboy]

Power-over-Ethernet uses cat 5 to send... (wait for it)... power over ethernet. There are plenty of phones and wireless access points powered this way. I think PoE runs up to ~350mA normally. If it can power a phone or wireless access point it can surely power a relay or two.

For a short run I doubt voltage drop would be very significant.

I would be more concerned about physical problems as GeeC mentions, ie durability in a high-vibration environment, rubbing etc.

[Dooley]

I wouldn't do it.
The gauge is a little on the small side.
The insulation is a little on trhe thin side.
It is likely to be solid core, and will be prone to break where your connectors are.
Use the trailer wire mentioned or source some other flexible multicore cable.

+

Even if it is stranded cat5/6 it isn't all that flexible or easy to run in the spaces and cavities of a car.

Sheath is usually PVC which isn't UV or exterior rated, doesn't have any sort of flame retardent properties, if that's any concern.

It'll work fine, but it's not ideal.

How many relays ? I don't see why you need 8 conductors. The earth side of the coils can all be tied together and go to the nearest chassis earth. So then you only need to run positive side 'triggers' off your switches.

[chimpboy]

Adding to the thing about the physical side rather than the electrical side of the problem... I recently wired up four relays and used fairly light wire for the ground side, just some black wire I happened to have sitting there. It's more than adequate electrically, but after mulling it over I have decided to replace all those wires with something heavier. The reason is that I think a good accidental tug on any of the wires, due to me doing something else in the engine bay, could stuff them up. Some heavier wire will be more robust against that kind of thing.

But this is just something for you to weigh up, it doesn't mean you can't use cat 5 if you think it is okay in your situation with the lower ability to withstand physical stresses.

[jlux3012]

i also think that you would be inviting trouble as far as the spade connections go, unless you were to solder the cat5 conductor onto the relay flag i dont believe you would be able to achieve a trouble free connection with a crimp.

[ledgend80]

myself i would just get a roll of 5 or 7 core trailer wire. that what i have done with my switch and relay setup. i went this way because it was already insulated and looked neat and tidy. and you have 5 or 7 different coloured wires so it was easier to identify which wire went where.

but hey if you have it there try it and see what happens. it may work and it may not.

[mickyd555]

You could use stranded UTP, commenly found in factory terminated patch leads which you can get up to 20m in length for under $20.

As stated though you would not be able to crimp on the spade terminals required. Trailer wire is about $15 for 5m 7 core roll at Supercheap, that should do the job no problems

[rustynuts]

My advice is dont use it in auto applications, all cabling in a vehicle should be multi strandard. Using solid conductor wiring ie shielded or unshielded twisted pair will only lead to fatigue at any joint or point of vibration and cause issues for you. There are plenty of other multicore stranded cables that are designed for this application.

[drivesafe]

Hi rustynuts, multi stranded cable is only slightly less likely to fatigue than single core wire if not secured properly.

The problem is not the cable type but how it is secured. I’ve seen plenty of trailer plugs and sockets with broken wires because the thing has not be secured away properly when not in use.

For the low current application that mk ute is planning to use the stuff for, once the wiring is finished and the cable is secured, he won’t have any problems because the cat5 is not heavy enough to bounce around.

[bushy555]

Have used old Cat 3 cable for years for running relays at the rear of my vehicles. Even have used two and three-pair telephone cable in some circumstances. Never had a drama yet. And if ya have 500 metres of the stuff (single or multi) just laying around, ya really not gonna go out and buy proper cable are ya?. Welp... I certainly wouldn't.

Relays should operate even faster if you were to use sheilded Cat 6 cable.

[r0ck_m0nkey]

The problem is not the cable type but how it is secured. I’ve seen plenty of trailer plugs and sockets with broken wires because the thing has not be secured away properly when not in use.

And with Cat5 it's quite the opposite.

Whilst cable securing is highly important, you just can't do it with Cat5. There's a reason why things like velcro cable ties are used to secure it, so that it is noit overtightened and doesn't concentrate the pressure to a small area, and that's partly due to avoiding damage to the inner cores.

So you either secure it to the correct tension which will allow movement in a vibrating environment such as a vehicle, or you do it tight enough to stop movement, but are then to tight which potentially damages the cores.

Add to the fact it's weak and has about a 50mm bend radius, it's just asking for potential failure. The stuff is crap for even it's correct purpose, let alone using it outside that purpose.

The stuff will work, just don't be surprised when it fails. I personally wouldn't use it even though i have hundreds of meters of the stuff in the shed, as i never like the thought of having to do something twice.

[drivesafe]

Whilst cable securing is highly important, you just can't do it with Cat5. There's a reason why things like velcro cable ties are used to secure it, so that it is noit overtightened and doesn't concentrate the pressure to a small area, and that's partly due to avoiding damage to the inner cores.

If this cable is tightly secured, the only thing thats going to be affected is the data transfer rate.

This cable is going to be used to turn relays on and off, it’s not being used to transmit HD TV data and as such, even if the cable is compacted, it’s not going to short out or the cable break apart.

Why must people insist on making a simple chore as difficult as possible.

This is not rocket science and the cable is not going to be carrying high speed data, hell, how fast do you expect a relay to turn on and off?

[r0ck_m0nkey]

If this cable is tightly secured, the only thing thats going to be affected is the data transfer rate.

Did you read that somewhere? I've installed and replaced enough of the stuff to know that the stuff doesn't handle physical stress very well, whether it's from over tightening cable ties, over bending or twisting, which has resulted in broken cores and that's without added stresses such as vibrations.

This is not rocket science and the cable is not going to be carrying high speed data

Wow, you must be a genius of some sort, did you figure that one out by yourself?

[chimpboy]

Well, the original question has been answered now anyway, so there's no need to drag it out until someone has "won" the debate.

(a) cat 5 can handle the load, in purely electrical terms
(b) there are reasons to be concerned about its durability in an automotive environment

The individual who owns the car can decide how much (b) matters to them in their application.

That's how I read it anyway.

[-Scott-]

Well, the original question has been answered now anyway, so there's no need to drag it out until someone has "won" the debate.

(a) cat 5 can handle the load, in purely electrical terms
(b) there are reasons to be concerned about its durability in an automotive environment

The individual who owns the car can decide how much (b) matters to them in their application.

That's how I read it anyway.

I agree.