atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring wire guage question

Ok, so you are installing a piece of low voltage equipment with 24ga 4 pair wire. The product you are installing says you need one pair of 18 gauge wire to get power to a door strike. By doubling, tripling or quading the wire, what would be the equivalent gauge of each additional pair?

1 pair 24 gauge = 24 gauge
2 pair 24 gauge = [21.5] gauge (?)
3 pair 24 gauge = [19] gauge (?)

More likely us low voltage guys will just use all 4 pairs to make one big pair. Is there some kind of equation or chart that would give us a general idea on gauge values?



[This message has been edited by A6 (edited March 24, 2004).]

Not sure about that, but -- I ran into a problem with door strikes in the past. Be aware that DC voltage drops really fast in a relatively short wire run. We wound up having to move the power supply to the door area, and controlling it with a relay! Pain in the neck to find a suitable source to plug the power supply into at the door end.

This is just an opinion, no scientific proof here. If the device calls for a specific gauge or higher it would be because of current flow, so in my humble opinion your not going to get the same current flow in using several pairs of smaller gauge wire verses the correct gauge. If it were AC power calling for 12 gauge electric wire you wouldn't tie two 4 pair 24 gauge together to power your equipment.
Bill

I would tend to agree with Bill, tying one pair together would I beleive just cut your resistance of the cable to more than half of the orgrinal conductor but would not facilatate the passage of more current. Interesting question.

What?! Lowering resistance doesn't increase current? Ohm's Law anyone?

yeah , according to the formula less Resistance would mean more current, but in this instance would the smaller diameter cable be able to take the increased current flow for any length of time before burning in two? I would'nt sleep well knowing I had it wired that way.

Yes. Let's say you used 4 smaller wires, the current would be divided across all 4, so that each would only carry 1/4 of the total. By the way, once years ago, my car battery went dead and the only thing I had to jump it with was a length of 25 pair cable. Biggest damned fuse you ever saw!

Now it's been a very long time since I've been to electronics schools, but if this old memory server me doesn't the current flow over the surface of the wire verses through the core? If I do remember right than the larger surface of 19 gauge would carry more current than several of 24 gauge. I could be all wet here. When I smoked and ran out of matches I used to light my smoke by taking 19 gauge wire across battery terminals. Wire got red hot in nothing flat. Not smart but it worked, your jumper cable reminded me of that.
Bill

justbill is right!
Current flows over the surface of the wire verses through the core. So lets look at the surface. A wire having twice the diameter of another wire will have four times the cross-section area (area = 3.1416 X radius squared)and therefore one-fourth the resistance.

Doubling the diameter quaddruples the cross-sectional area, reducing the resistance to one-fourth. The rest is ohms law.



[This message has been edited by CMDL_GUY (edited March 24, 2004).]

A6:

Valcom tech support says that using telephone cable (doubling up) is just fine for their horns---I've been doing that with 24 volt PSs for quite a while. Its also one of their selling points that they push. Also---NT has you run power through telephone cable ending up in a 6 pin jack(for their KLMs. For fun---hook up a 24 volt PS and test different kinds of wire or cable. See what happens on your multimeter. Maybe it only makes a difference on a very, very long run.