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Old 12-28-2010, 03:19 PM   #1
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Dimmer switch with Hot & Neutral wire ?


i don't understand this network, seems it is wrong but seems to work just fine. maybe you can explain it?

i have 3 lights all running off one dimmer switch. there is a single 14/3 wire (red,black,white) entering the switch box. in the same box is another dimmer controlling a separate light (i.e. no 3-way switch here).

the white wire is wrapped in black tape, probably the electrician is giving indication that this white wire is being used as a HOT. it measures infinite impedance to ground (and to the other wires) so probably a good guess. this HOT wire goes to one terminal on both switches.. so far so good.

on the other side of the dimmer switch A is a red wire.
the other side of dimmer switch B is the black wire.

ok, no problem here either.. i am thinking that the RED and BLACK are also HOT, so the dimmer switch is interrupting only the HOT wire.

but when i measured the RED and BLACK wire with respect to the metal box i get 5 ohms, and it beep on my multimeter.

huh? seems each dimmer is wired such that it is in series with the loop. HOT wire and NEUTRAL connected to the dimmer.

the wiring is confusing me because it is against my conventional thinking of how wiring should be. my thinking is that switches should only interrupt HOT wire, never the neutral. this is for safety.

what do you think?

by the way, the light seems to work just fine.

Knucklez

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Old 12-28-2010, 03:33 PM   #2
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Dimmer switch with Hot & Neutral wire ?


The white wire might be unused. Black and red may then be used to connect to the switch or dimmer.

You will measure a low resistance from the hot to neutral (or ground) because the light bulb is completeing that path and a cold (unlit) incandescent light bulb has a fairly low resistance (just a couple of ohms).

If there is one 3 wire cable going to a box with two switches, then the white is supposed to be the feed (raw power) to the switches and the red and black are returns (switched power) from each switch respectively.

There is talk of including in the next version of the National Electric Code the requirement of using 3 wire cable from a powered light fixture box down to an otherwise unpowerd single switch box. The white wire would be the neutral for future continuation to other boxes or to provide a neutral for some kinds of dimmers.

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Last edited by AllanJ; 12-28-2010 at 03:43 PM.
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Old 12-28-2010, 04:22 PM   #3
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Dimmer switch with Hot & Neutral wire ?


Quote:
If there is one 3 wire cable going to a box with two switches, then the white is supposed to be the feed (raw power) to the switches and the red and black are returns (switched power) from each switch respectively.
yes, this is how i think it should be and i believe matches my wiring. but .. the switched power RED/BLACk .. why do they measure so low impedance, you are saying it is because it is going through the light bulb, and back to the panel, to the ground bar. so the 5 to 10 ohms i was measuring was the light bulb element. interesting. thanks for the info!

Knucklez
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Old 12-28-2010, 04:24 PM   #4
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Dimmer switch with Hot & Neutral wire ?


You don't have enough wires for either of those switches to be three ways.
Power comes in on the white marked black. It goes though each dimmer and back to the respective lights as switched&dimmed power on the black and the red wires. There is no neutral wire in that switch box.
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