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.

Those pesky doorstikes! Under 50ft 24g single pair usually works. From 50 to 120ft double pairing. Of course you could always keep some CL2 around.

Guess the only question I have left on this is if you have to double up, triple up, or quaduple up you still have to pull the wire so why not pull the proper gauge for the job to begin with? With that I'll leave you with button and buzzers, I can understand that!
Y'all have a good one.
Bill

An interesting side note -- in the 70's when copper prices rose steeply, they started making Romex house wiring out of aluminum. However, unlike copper, aluminum conducts through the core. So, when they put on switches and outlets desined for the surface-conducting copper, there was resistance and therefore heat between the core and the device. Lots of house fires! Nowadays, when you get aluminum Romex, it has a thin copper plating.

[This message has been edited by chuck (edited April 02, 2004).]

Don't have anything to say about this post. Just wanted to drag up the oldest "Real" post i could find.(Everybody else is!!!)

Chuck:

While we stray on this subject...........

Aluminum wiring for general circuit wiring started in the mid-60's. When it was determined that it had deficiencies, the "copper coated" aluminum wire was developed as a solution.

This wire, known as "copper-clad aluminum" lasted about five years, but using it in electrical wiring was outlawed YEARS ago, some time in the '70's in most places. The only LEGAL aluminum wire allowed these days is #8 and larger. Any copper-clad aluminum wire that you see newly-installed is not allowed.

Anyway, back to the original subject as JustBill mentioned, if the device calls for 18AWG, just do it. No need to stock #18 wire in a telecom house, go to Home Depot and buy it by the foot. Do what you are asked and be compliant. That way, you did what you were asked to do instead of trying to "trick" a piece of whatever wire you have on the truck into doing the job.

Door strikes work on whatever you give them, as long as the length is reasonable.

Here I go again directing you all to my signature....................

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Ed
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How come there's always enough time to go back and fix it a second time?

[This message has been edited by ev607797 (edited August 16, 2005).]

I would join you in your quest but....
its already hard enough to get these newbees to not do that. Lucky it only runs in waves LOL

Aluminum conducts through the core? I'm going to have to call BS on that one.

Oxidation of the aluminum surface of the wire is the trouble. This reduces the surface contact area of the wire and the terminals. Increased current to area ratio makes for higher power dissipation (heat) at the point of contact.

Sorry about misspelling ratio

[This message has been edited by RedTail (edited September 17, 2005).]

I think everyone might be overlooking something. Isn't 18g wire used in most low volt applications stranded? Therefore having a whole lot more surface area than double or tripled solid core cat3/5.

A constant current (DC) flows evenly thru the cross section area of a conductor. Current in a conductor generates magnetic lines of force around the conductor. Magnetic lines of force crossing a conductor generate voltage/current in the conductor. As current increases the MLF expand. As current decreases the MLF contract. The voltage generated by the MLF is in opposition to the change in current in the conductor. When an Alternating Current (AC) reverses direction, all of the magnetic lines of force collapse to the center of the conductor. When AC is flowing thru a conductor, the parts of the conductor farther from the center of the conductor have less resistance to the flow of the current. Stranded conductors do have more surface area but the current flow is just the same as solid. A copper tube will care more AC signal than a solid copper rod of the same cross section area.

Just to clarify things, DC and low frequency AC travel through the center of the wire, as frequency goes up the current moves to the surface, typically around 3 MHz and above. For frequencies we work with, usually DC, audio, and digital below 1 MHz, the current travels through the center.

Has any one had problems with using jelly beans to patch phone lines

Sorry I tried to make a new post. I dont see where to go.

Top of page "Post New Topic" and no I haven't had problems with beans, but I do know there are several manufactures and I'm sure they're not all equal.

ANSWER TO WIRE GAUGE QUESTION

2 pairs 24 awg = 18 awg
3 pairs 24 awg = 15 awg
4 pairs 24 awg = 12 awg