Home>Discussions>ELECTRICAL & LIGHTING>Need advice testing 22 AWG wire runs for short circuits
5 posts / 0 new
Last post
zknower
Need advice testing 22 AWG wire runs for short circuits

Hi All:

I am installing a simple TALK/LISTEN/DOOR intercom system in my 3-family 1850s brownstone in Brooklyn, NY. The old doorbell wiring was terrible and unreliable.

I have run 22 AWG wire in the walls everywhere I need it. Next step will be to hook up my transformer, amplifier, apartment stations, and the door entry unit to the wiring where it all meets in the basement. I bought all of these items in a kit from a supplier.

Here's my question: The kit instructions say to check my wiring for shorts/functionality before hooking everything up and connecting the power. Is there an easy way to to do this? The wiring is brand new, so I assume I'm just looking to see if a staple landed in the wrong place somehwere before I close the walls up.

I'm happy to buy a meter or whatever if necessary. Also open to whatever old-fashioned tests there are (9V battery and an line tester?.... I have no idea.) It's my first time working with low-voltage wire, so any advice is appreciated. Thanks!

keith3267
Re: Need advice testing 22 AWG wire runs for short circuits

You can test for continuity by twisting one end of the wire pair together and putting an ohmmeter or VOM in the ohm position. Then separate the pair and check again. But the definitive test would be a check of the open circuit with a megohmmeter aka Megger. This is a pretty expensive piece of equipment but some large electrical contractors would probably own one. I don't know if you can rent them anywhere. With LV (signal) wiring, I don't think it is really necessary, a check with a VOM should be enough.

Just checked, Amazon has a cheap Megohmmeter for $50 that would do for LV cable structures, but I still think a VOM check would be enough.

zknower
Re: Need advice testing 22 AWG wire runs for short circuits

Perfect, this is exactly what I needed.

A follow up. I'm using 5-wire (two twisted pair, IIRC, and then a fifth solo) and the ends are 3 floors apart.

Can I twist all five together and check the reading, and then disconnect all and compare?

Or will that skew my results and I would need to check them pair by pair.

Thanks.

keith3267 wrote:

You can test for continuity by twisting one end of the wire pair together and putting an ohmmeter or VOM in the ohm position. Then separate the pair and check again. But the definitive test would be a check of the open circuit with a megohmmeter aka Megger. This is a pretty expensive piece of equipment but some large electrical contractors would probably own one. I don't know if you can rent them anywhere. With LV (signal) wiring, I don't think it is really necessary, a check with a VOM should be enough.

Just checked, Amazon has a cheap Megohmmeter for $50 that would do for LV cable structures, but I still think a VOM check would be enough.

zknower
Re: Need advice testing 22 AWG wire runs for short circuits
zknower wrote:

Perfect, this is exactly what I needed.

A follow up. I'm using 5-wire (two twisted pair, IIRC, and then a fifth solo) and the ends are 3 floors apart.

Can I twist all five together and check the reading, and then disconnect all and compare?

Or will that skew my results and I would need to check them pair by pair.

Thanks.

To clarify: I meant twist all 5 together at one end, but then check pair-by-pair at the other end. I'm assuming if I'm checking 2 at a time to make a closed circuit, the other three wires that are only connected at the opposite end—but not at the end where I'm testing—won't throw things off?

Re: Need advice testing 22 AWG wire runs for short circuits
zknower wrote:

To clarify: I meant twist all 5 together at one end, but then check pair-by-pair at the other end. I'm assuming if I'm checking 2 at a time to make a closed circuit, the other three wires that are only connected at the opposite end—but not at the end where I'm testing—won't throw things off?

True, twist all the wires together at one end then check that all wires show conductivity to each other at the other end with a VOM, set at the lowest setting. Expect a reading of .3 ohms or less.

Then untwist all the wires and check at the other end with the VOM set at the highest setting for shorts.
Expect a reading of infinity, which is the same as you would get if you didn't hook the meter to the wires.
Be careful not to touch the wires, since the resistance of your fingers will be measured.

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.