Cat5 for power supply to MagLock

[d000hg]

I was quite surprised that our electrician has laid what looked like a network cable to run 12V DC power to a MagLock we're going to install on our gate. I asked him and he's actually run 2XCat5 cables, citing distance/voltage drop as the reason for having two of them.

I didn't want to distract him further but is this normal practice and if so why? Our MagLock is specified to draw about .5A at 12V as far as I understand it.

 

[Handymanjo]

Hope it's ducting grade cat5

 

[d000hg]

I have no idea what you just said. Please explain what that is why it matters?

 

[sparkymarka]

You can run it at 24v if your concerned about voltage drop

 

[Handymanjo]

Ducting grade cable has a hard pvc outer coating with helps protect the inner cores from damage. Standard pvc date can damage easily if not protected correctly.

 

[d000hg]

Ducting grade cable has a hard pvc outer coating with helps protect the inner cores from damage. Standard pvc date can damage easily if not protected correctly.

I see. It's running in a duct underground and he seems to know his stuff.

I'm just curious why not use a normal cable?

 

[Handymanjo]

What is a normal cable ?
Is the mag lock for automated gates,or just a mag lock to secure a pedestrian gate ?

 

[d000hg]

What is a normal cable ?
Is the mag lock for automated gates,or just a mag lock to secure a pedestrian gate ?

Normal cable is 1 or more isolated wires. Cat5 is a bunch of very thin, paired wires. And costs more. So what purpose does it serve to carry current to a simple switch over a regular old lighting cable or whatever?

It's just a maglock. No gate actuators or anything like that.

 

[sparkwright]

Cat5e sounds quite typical for a maglock.

How long is the cable run?

 

[d000hg]

Perhaps 20m tops, definitely in the 15-20m range.

 

[endecotp]

Apparently Cat 5e is supposed to have a DC loop resistance of about 0.2 ohms per m per pair. If you put all four pairs in parallel, for 20m that would be 0.2 / 4 * 20 = 1 ohm, so at 500 mA that would be a voltage drop of 0.5 V. I’d be surprised if your 12 V electromagnet would not work at 11.5 V. (Have I got those numbers right?)

 

[JM2]

I'd have used the thicker (not super-thin) alarm cable after due consideration (length, current draw), never cat or telephone cable.
Hopefully he has at least used stranded cable - the solid (better for networks) is quite brittle - and protected it well.
The proper answer is of course, to use some suitably rated (dc) cable for the environment it is in (but that'll cost more than some cat cable kicking around).

 

[JohnW2]

Apparently Cat 5e is supposed to have a DC loop resistance of about 0.2 ohms per m per pair. If you put all four pairs in parallel, for 20m that would be 0.2 / 4 * 20 = 1 ohm, so at 500 mA that would be a voltage drop of 0.5 V. I’d be surprised if your 12 V electromagnet would not work at 11.5 V. (Have I got those numbers right?)

You appear to have got your arithmetic right so, if your "0.2Ω per m per pair' is correct (I don't know), then I agree with all you say.

However, it isn't a type of cable which I personally would be inclined to use for such a purpose and I can but presume that the only reasons could be either cost or 'availability' ('got some Cat5e in the van')!

Kind Regards, John

 

[EFLImpudence]

100mΩ/m is 100/18.3 = 5.46 x that of 1mm², therefore the wire must be 1/5.46 = 0.183mm² csa and 0.483mm. in diameter.

Is that about the size of Cat5.

 

[sparkymarka]

whats the Maglock being powered from in the first place ? If it’s an alarm psu with battery back up then it’s running at 13.8v dc anyway