weird house wiring problem

[Mosey]

I’m no expert at house wiring, but I thought I understood the basics. I’m replacing a bathroom light with a light that has an exhaust fan. There’s only one switch there now, so I needed to add a second switch to have one control the light and one control the fan. So, I started by adding another wire (I got lucky here and didn’t have too much trouble running a new wire down from the attic to the box).

Before I even hooked up the new wire or installed the new light, I removed the existing switch and replaced it with a new switch that has 2 single pole switches that I found at Lowes. It fits in a single wide switch box and the switches flip sideways instead of up and down. So, I connected the wires that went to the old switch to one of the switches on the new switch. I connected the black (hot) wire to the hot side of the switch and the white wire (which will become a hot wire when the switch is turned on) to one of the switch terminals on the other side. I didn’t connect the ground wire to anything yet. Simple right? When I turned the breaker back on, the light came on even though the switch was turned off! Flipping the switch back and forth made no difference. The light just stayed on all the time. I tried the other switch and the same thing. So, I took it off and put the old switch back on and it worked like it should.

So, I took the old switch back off and turned the breaker on. I used a volt meter to measure from the black wire to the box (metal) and it read 125V, like it should. I measured from the white wire to the box and it measured 0V, like it should. I put the new switch back in and the light stayed on all the time again. I called Lowes and they said they’ve never had anyone return a switch because it was bad and asked me to double check my wiring, so I did. But, I got the same results. I tried switching the wires so the white wire went to the hot side of the switch and that made no difference, so I switched it back and did some more measuring. From the ground on the switch to the box, it read 125V! That did not seem right to me. So, I took the switch off and did some measuring with and ohm-meter. I connected one lead of the ohm-meter to the hot side of the switch and the other to one of the switch terminals on the other side. When I turn the switch on, it goes to 0 ohms, like it should. When I turn the switch off, it goes to infinity, but not right away, it gradually goes up and takes 12 seconds to get to infinity. Also, there are no shorts between the ground and any of the terminals.

At this point, I determined that the new switch as acting strange and must be defective, so I put the old switch back in and forgot about it for a while and went and worked in the garage. But, it kept bugging me, so I took my garage light switch out and put the new switch in place of it. It worked perfectly!

I have a BSEE, but my expertise is with digital electronics, not house wiring and I’m stumped on this one!

 

[Inspector507]

Danny,
I've got 26 years in the electrical field and it has me stumped too. Do you have a way to snap a pic of your switch after you connect it? I'll look at it and see if something looks goofy.

 

[AndyR]

All of the white wires should be tied together, as they are the neutral side of the circuit. You should also run ground to the switch box (if metal) and to the fan/vent enclosure. The black side is your hot side. You should only have black wires to your switches (or red if you are using a 3 conductor cable - didn't sound like you were though). The "input" side of your switches should be the black feed wire from your breaker box and should be common to both switches. The output of one switch should be the black wire to your light. The output of the second switch should be the output to your fan. NEVER switch the neutral (white) side - only the hot (black) side.

You may also want to confirm that your ground is good back at the breaker box. The ground is a safety measure to prevent things like switch boxes riding up to 120 VAC if the neutral opens up. You will note that ground wires are usually smaller - they are for protection - not for load carrying. The only place you want ground and neutral tied together is at the breaker box. One last thing - this being a bathroom, you should be running off of a ground fault protected circuit (GFCI). You either should have an outlet "upstream" of your switch that is a GFCI type or a GFCI breaker (much more expensive then the outlet).

Sake Mense?

 

[Inspector507]

Andy,
All of that made sense to me, but you can also "back-feed" a switch. In that case there would be a white wire on the switch. Sounded to me like he had a switch loop with a white and a black wire on the old switch.

 

[Mosey]

Jerry, I don’t have a digital camera or a scanner. So, I’ll try to describe it better. I took the existing black wire and connected it to the side of the switch where there is a breakout tab (which I did not break). It’s labeled “+ LINE +” and the screw has a black coating on it. I connected the existing white wire to the other side of the switch on the bottom screw. It has no label and it’s a bright brass colored screw. I did not connect anything to the other bright brass colored screw on the top of the same side or to the green colored screw in the middle of that side (which is connected to the metal part of the switch that attaches the switch to the box). I also tried connecting the white wire to the top screw on that side when it didn’t work, but it made no difference.

Andy, I am breaking the hot side of the circuit. The “wire” has 3 individual wires, 1 black, 1 white, and 1 bare, with another layer of black insulation going around all 3. The black one is hot all the time, so I’m assuming it goes back to the breaker box via a junction box. I’m also assuming the white one goes to the hot side of the light via the junction box. So, it’s actually a hot wire, but it’s white. The way I understand it, it’s supposed to have been painted black on the ends but whoever wired the house didn’t do that. The bare wire is connected to the metal switch box. The house was built in 1978, so all the boxes are metal. I’m also assuming the other side of the light has a white wire going back to the breaker box via the junction box. There is a ground fault protected outlet plug in this bathroom, but it’s on a separate circuit. The light switch was just a normal switch. Maybe the new switch I have is only supposed to be used in a ground fault protected circuit? Although, if that’s the case, it shouldn’t have worked in the garage.

I went to Lowes today and bought another new switch just like this one, plus 2 others that are slightly different (they fit into a different type of switch plate and have rocker type switches). So, when I get home tonight I’ll see how these act.

 

[AndyR]

Yup - if the previous run had power to the appliance and a "switch run" out to the switch you would have exactly that - good catch.

 

[Inspector507]

Danny,
Sounds as if you hooked it up properly. The only thing I would caution is, usually it is the black wire (in this type of situation) that is the return to the light, but they did some screwy things back in the 70's also.

 

[beenthere]

Get someone to help you that knows wiring. From what you describe, you are hooking it up wrong, and it is not a bad switch. Also, you are getting confused with the other responses, as they either don't understand your situation, or are talking about possible situations that you do not have.

For your safety, get some help.

The three wires you describe - black, white, and bare copper - are hot, neutral, and ground in a 2 wire w/ground cable. The black should feed one side of the double switch connected by a strap. The other side of the switch should have two separate terminals - one for each switch. From each of those terminals should be a black wire running to the fan, and another black (or red) wire running to the light. These are hot when the switch makes them hot. The white wire feeding into the box should be connected to the one white wire going to the fan/light (if you have three wire w/ground cable. If you have 2 wire w/ground cable, then both of the white wires should be connected to the white feed wire. The bare copper ground wires should be connected in the box and be connected to the box, switch, and the fan chassis. At the fan/light end, there should be one or two white wires that should be connected to the white wires comming from the switch.

Be safe, and know what you are doing, and do not guess. You may accidentally have the chassis of the fan/light wired to 110 and just make the connection between it and ground. Curtains!!!

 

[Mosey]

"usually it is the black wire (in this type of situation) that is the return to the light"

Jerry, I've been wondering which way it was supposed to be. It appears that it was done backwards in this case, since the black wire is hot all the time. I guess I'd better dig around some more in the blown in insulation and find that junction box and take a look inside!

 

[MossRoad]

Did you wire it like either of these circuits?

I left the ground off on purpose.