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Introduction: I'm in the alarm industrie and there is something we all do but I never questioned my self if it is good or not. Recently, some guy from the technical support department of honeywell told me that is not good.

What:

  1. We use most of the time a wire 4/22 to do our work.
  2. When we have to "power" our equipment we normally "double" the wire like : "red-yellow" / "Black-green" to drop the resistance.

I know that do not make a bigger wire but it should help.

Situation: - The power supply is 9vDC - The manufacturer said : No more than 11' and double wire do not change anything.

The Question: What are all the real impact of doubling wires in any situation ? (AC and DC, power, communication, etc)

Thanks

15 Décembre 2015

The guy from the manufacturer told me that the method of using 3 wire to match the AWG do not apply because it is in DC ...

It is true that it will not react the same AC / DC ? I know that DC drop faster than AC but how it is accurate in this situation ?

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  • \$\begingroup\$ In my experience at least, if a manufacturer specs a certain gauge wire, we use that wire or larger. That way if something untoward happens the fault is placed on the proper shoulders instead of on engineering because we did what "worked", but didn't follow specs. Your questions is kind of too broad for this site, and seems more like something you should google and research yourself. Making your question specific to your situation would make it less broad and more appropriate. \$\endgroup\$ – I. Wolfe Dec 14 '15 at 20:38
  • \$\begingroup\$ I totally agree about respecting manufacturer spec. But somethime we have to deal with people who don't. And if I want to change those "hold" mentality I need to explain why. I understand the basic of electronic but not enough to tell to another guy you should not do this because .... And this is what i'm looking for. What is the real impact of doubling wire ... It is like removing the 1/3 of the resistance ? No impact at all because 9v DC will drop unless you put 6/22 ... This is what i'm trying to understand to be able to told to the hold guy why they should follow manufacturer spect \$\endgroup\$ – Jonathan M. Dec 14 '15 at 20:53
  • \$\begingroup\$ And yes I'm googling and search and make call to find my answer. \$\endgroup\$ – Jonathan M. Dec 14 '15 at 20:55
  • \$\begingroup\$ This should help you some: electronics.stackexchange.com/questions/110901/… According to the top answer there, in place of a 2/18, you would need 2 wires of 4/21. So to get the same safety you would need larger wires, or 3 of the 4/22. As said in the second answer, it is the circular cross section that you need to be aware of. So just tell these people that they are reducing the cross section of the wire, thus not meeting the required specs. \$\endgroup\$ – I. Wolfe Dec 14 '15 at 21:16
  • \$\begingroup\$ I'd also worry about connecting two wires to a terminal only designed for one. Maybe that's not a problem in this case. \$\endgroup\$ – pipe Dec 14 '15 at 21:58
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In order to mount a proper argument, if the resistance of the 2/18 versus the resistance of 4/22 configurations is at issue, it's only necessary to consult a copper wire table (shown below) to resolve the problem.

Looking at the entry for 22 AWG indicates a resistance of 16.5 ohms per thousand feet, while for 18 AWG we find a resistance of 6.51 ohms per thousand feet.

Paralleling two one thousand foot long strands of #22 will result in a total resistance of:

$$ Rt = \frac{16.5\Omega \times 16.5 \Omega}{16.5\Omega + 16.5\Omega} = 8.25 \text { ohms} $$

Then, since a single thousand foot long strand of 18 AWG will have a resistance of 6.51 ohms per thousand feet and a paralleled thousand foot long double strand of 22 AWG will have a resistance of 8.25 ohms, for equal lengths the 22 AWG arrangement's resistance will always be higher than the 18 AWG's

enter image description here

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    \$\begingroup\$ Indeed - a difference of 3 AWG is roughly double/half the cross-sectional area/resistance. And not surprisingly, 2 x 22 awg is pretty close to 19 AWG for resistance and cross-sectional area. \$\endgroup\$ – Ecnerwal Dec 14 '15 at 22:06
  • \$\begingroup\$ Could it be that AWG is somehow related to dB? \$\endgroup\$ – EM Fields Dec 14 '15 at 22:17
  • \$\begingroup\$ Not related to dB except in the sense that they are both logarithmic. An increase of one wire gauge is a 26% increase in cross-sectional area. \$\endgroup\$ – user28910 Dec 14 '15 at 22:25
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The problem is that loss of one conductor / wire in a power circuit will be undetected and overheating or large voltage drop will be a problem.

In a communication circuit several problems could occur including mis-matched impedance and poorer noise immunity - although it might actually help in some configurations.

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  • \$\begingroup\$ Yes i'm aware of the principe of impedance. I receive a few notion in my training. There concern though where more about the video field than the alarm. :) \$\endgroup\$ – Jonathan M. Dec 14 '15 at 20:27
  • \$\begingroup\$ In all the manual I have read, They are more concerne about the "data bus" from keypad and they suggest normally to use 2/18 but I can tell that the majority of the industry use 4/22 \$\endgroup\$ – Jonathan M. Dec 14 '15 at 20:28
  • \$\begingroup\$ You didn't mention video in your question. \$\endgroup\$ – Transistor Dec 14 '15 at 20:29
  • \$\begingroup\$ In this case, there where saying that the 9vDC need a 2/18 other wise There will not have enough power. The problem is that it is working with the 4/22 with double wire so it is difficult for me to argue with other tech and the field to make them install the proper cable. So I need proper argument :) \$\endgroup\$ – Jonathan M. Dec 14 '15 at 20:32
  • \$\begingroup\$ no I din't, I was just referring to the fact that during my training at school (where I learn to become a tech) they where talking about impedance and how it is working but the relation to it was with the video and not with other area of the training such as power true 4/22 and doubling wire \$\endgroup\$ – Jonathan M. Dec 14 '15 at 20:34

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