[Ryan0751]

I'm trying to replace some old style (turning knob) dimmers with X10 dimmers. The dimmers control some incandescent recessed fixtures in my living room.


I've removed the old dimmers, and in the junction box I found 2 black wires connected to them. On the new switches, they labeled the "line" versus the "load". I understand these concepts, line goes to the breaker box, load goes to the lamps, and neutrals should be connected together inside the junction box.


The problem I have is that I don't know how to determine which is which... does it even matter? It looks like with the old switches they can be connected in either way. Is there and easy way to figure this out with a multimeter?

 

[Toxarch]

Flip the breaker back on, grab hold of the ground with one hand and then grab one of the blacks with the other hand. If you get a shock, that is the line voltage wire. OK, just kidding. Don't do that.


The "old" dimmers can be wired either way. If the X10 dimmers are labeled, better to wire them that way. A cheap miltimeter would be the way I would go. Or, there is a voltage detector sold at HD or Lowe's you could use. It looks like a big pen. When you get it near a hot wire, it will beep and flash a red light.

 

[Toxarch]

Oh yeah, how do you do it with a multimeter. Make sure the two black wires are not touching anything. Then flip on the breaker. Set the multimeter to read a voltage above 130 volts. Test the voltage between either the neutral (or the ground) and each of the black wires. The one with the voltage is the line wire. Turn off the breaker and connect the new dimmer.

 

[cgblack]

To figure it out with a multimeter, first go to the breaker and shut it off. Then remove the dimmer, and pull the two black wires out of the junction box so that they do not touch anything (be sure they are not even near anything!) Separate the two black wire (up and down for example) so that once it is identified, you can remember which is which without having to immediately label it while it is still live.


Go back to the panel and reenergize the circuit. Set your multimeter to the 200V A/C range and, assuming the junction box is 1) metal, and 2) grounded, touch one probe to the junction box and the other to one of the black wires, then the other. The one that reads approv. 120V is it. If the junction box is not metal, touch the probe to the bare grounding wires in the junction box. BE CAREFUL not to short anything to the live wire. There is enough voltage to kill easily, and even to arc weld and melt whatever creates the short.


Go back and switch off the breaker. Return and wrap a piece of red electrical tape around the wire that was NOT the live wire. This is a standard method of indicating a switch live wire. Connect the black wire to the live x10 connection and the red marked wire to the load. You will, depending on the x10 dimmer, probably need to connect the neutral (white) as well, and don't forget the ground. Any connection (wire nut) that you are taking apart needs to be clipped back and restripped and a new wire nut placed on it, if you wish to meet code.

 

[Ryan0751]

Hmm... I was thinking this way too, which would be safer:


1. Turn off the breaker


2. Disconnect the existing switch


3. Using the continuity setting, test for continuity between the white and both blacks. The one with continuity would be the load (since the blub would complete the circuit).


Wouldn't that work?

 

[cgblack]

Use a resistance setting, instead of the continuity setting, since the bulb will probably read as a load instead of a completely closed circuit. One wire will read as an open circuit, the other will probably show a few ohms.

 

[Larry Fine]

Quote:

Originally posted by cgblack Any connection (wire nut) that you are taking apart needs to be clipped back and restripped and a new wire nut placed on it, if you wish to meet code.

Graeme, in all of my wiring years, that's one I never heard before! Can you find that in the NEC and post the section?


Also, everyone, you don't have to disconnect the original dimmer at all to test for hot. Just make sure the dimmer is turned off. In case anyone is thinking about the trickle current, the filament(s) will still pull the voltage down to near nothing, similar to a 'pull-up' or 'pull-down' resistor on an IC.


The two-wire X-10's are not polarity sensitive; the blue and black are interchangeable. However, the three-ways and the ones that require neutrals are, and connection colors/terminals do matter.

 

[Toxarch]

Ryan, the continuity test would work, but some multimeters don't have that and others read it as a really weak signal.


Larry, thanks. It totally slipped my mind that the dimmer didn't have to be removed. And would there really be a trickle current? I thought all dimmers have to have a type of mechanical break in the current at "off".

 

[Larry Fine]

Tox, you're correct. UL requires a complete disconnect position for safety when bulb-changing, etc. That's why X-10's have the little slide switch. I just threw that in because my mind's ear heard someone mentioning it.

 

[cgblack]

Quote:

Originally posted by Larry Fine Graeme, in all of my wiring years, that's one I never heard before! Can you find that in the NEC and post the section? Also, everyone, you don't have to disconnect the original dimmer at all to test for hot. Just make sure the dimmer is turned off. In case anyone is thinking about the trickle current, the filament(s) will still pull the voltage down to near nothing, similar to a 'pull-up' or 'pull-down' resistor on an IC. The two-wire X-10's are not polarity sensitive; the blue and black are interchangeable. However, the three-ways and the ones that require neutrals are, and connection colors/terminals do matter.

I found this in a search on Mike Holt's NEC forum.


First post


The ground wire was hooked to the receptacle and to the metal box. I was curious because the connection of the three NM cable gd. wires was made by twisting the wires together, no wire connector or crimpping sleeve. The bare ground wires were just twisted together 3 or 4 turns. Is that an acceptable practice today in residential wiring.


Response


No. That is a good way to start a fire. Section 250-8 requires the use of listed connectors for all grounding and bonding connections. In the '96 code it was section 250-113.


I do not have access to the NEC myself. Hope this helps.


I also found this.


It mentions NEC 250.146 & 250.148(A)

 

[Ryan0751]

Thanks for all the suggestions... I ended up buying an inexpensive voltage sensor at home depot. With the power on, I checked voltage on one wire with the switch in the on then off position. The one with the constant current I assumed was line, the other load.

 

[Larry Fine]

Ryan: Exactamundo!


Graeme, that doesn't mention having to re-strip undone connections.

 

[cgblack]

Sorry Larry, I confused two different threads. In another thread you had mentioned how to wire up a junction box, and I commented on the need for wire nuts on grounds, and I thought this was that thread.


Not enough caffeine!!


As far as restripping, as long as the wires have not been damaged in the process of taking them apart, you could reconnect them. I would be hesitant to disconnect and reconnect them too many times, since the wire nuts cut into the conductors. Also if they are old connections, there may be some oxidation on the wires, so it might not be a bad idea to cut them back.


I mis-spoke when I mentioned it was a code requirement, sorry! It's probably more of a good practice, especially in older construction.