120v electrical wiring

Ok... dumb question maybe since I'm not an "real" electrician, I just play one on TV.

In my bathroom remodel, I am adding a GFCI outlet in a double-gang box beside two horizontal switches (light/fan). The old wiring had no fan and just a switch above the tub for the light.

Anyway... I ran 12/2 through the ceiling down to a duplex box beside the vanity. From there, I fed 14/3 back up to where the fan/light will be, 14/2 up to where the vanity light will be. Both lights and the fan lead are off the "load" side of the GFCI so they get cut in case of GF.

So, from the 12/2 feed, I attached the black and white to the "line" poles, then used a black jumper from the "load" pole over to the dual switch. From the switched side, the red and black in the 14/3 go up to the light/fan. All of the grounds and together and all of the commons go to their respective places.

Here's the fun part. With the GFCI reset, I get 124v everywhere I'm supposed to. With the GFCI tripped, I get 45-70v out of the load side and THROUGH the switches even though they're off. Its all brand new stuff, but I thought maybe I got a bad switch or GFCI, so I replaced the switch with another one... Same thing. I swapped out the GFCI... same thing.

Any ideas?

I just verified this as being what I have. The picture doesn't show grounds, but they're all there. With the GFCI reset, I get 124v everywhere I should. With it tripped, I get 45-70v at A1 and B1. WTF.

Ok, I think I found the issue. Further testing revealed that the original wiring feed had reversed polarity. What I thought was line was actually common. I switched them around and it seems to be behaving

... but ... I'm still getting 5 volts to the red and 2 volts to the black at the ceiling 14/3. Its not enough to shock me at all, but it keeps tripping the GFCI as I'm trying to work with it. Even when I put the test leads on, its tripping it. Is that normal? I'm used to getting a little voltage everywhere (heck I get .25v between my fingers if I hold the leads) but 5v? What is normal? We're talking about an isolated run of about 10 feet from the switch to the ceiling box.

My limited home wiring says you have a bad ground somewhere or an open neutral

Grtechguy wrote: My limited home wiring says you have a bad ground somewhere or an open neutral

I thought so too, but I'm getting good voltage between line and common and line and ground... its just that the line and common were switched

... unless you're talking about the 5 volts.

If you're using a digital multimeter to measure the voltages you may be seeing phantom voltage: http://en.wikipedia.org/wiki/Phantom_voltage

Phantom voltage (sometimes referred to as ghost voltage) is voltage that appears in an electrical conductor such as a wire, even though the wire is disconnected from an electrical circuit. The term is often used by electricians, and might be seen, e.g., when measuring the voltage at a lighting fixture after removing the bulb. It's not unusual to measure phantom voltages of 50-90 volts when testing the wiring of ordinary 120V circuits.

Causes of phantom voltage may include: Capacitive coupling in which there is capacitance (a build up of opposing electric charges) between the conductor in which the phantom voltage is detected and nearby circuitry. Inductive coupling in which the magnetic field produced by current flowing in a nearby circuit induces current flow in the conductor where phantom voltage is detected. The effect is almost always seen as the result of using a digital meter. The input is high impedance and can't bleed off the phantom voltage effect. Using an analogue meter (one with a needle) will usually quickly remove the phantom voltage and give an accurate reading. Using solenoid tester will always give an accurate reading.

Why 2 power (red & black) to the fan/light? 1 from A1 and 1 from B1. If the switches are jumpered I would think that would cause some issues.

Not sure on the phantom voltage, but I must ask why 12/2 to the GFCI and then a smaller gauge to the rest? I hope you have it fused at 15 amps with the way you have it set up as that is all the 14 gauge wire is good for. I know if you put a wiggy between the hot lead and the ground it will trip a GFCI. Could you be doing that to cause this trouble? The wiring diagram you show looks okay to this trained professional, but the different gauge wires has me worried.

The lighting loads are fixed. He's not gonna pull 20A through the 14 gauge wire.

Unless, of course, he puts in a 2400w light bulb!

stuart in mn wrote: If you're using a digital multimeter to measure the voltages you may be seeing phantom voltage:

Yup - Fluke digital mulitmeter. I had just not seen that much voltage before. Makes sense.

wlkelley3 wrote: Why 2 power (red & black) to the fan/light? 1 from A1 and 1 from B1. If the switches are jumpered I would think that would cause some issues.

The supply side of the switch is jumpered. You can break out the tab to supply each switch with its own line, but I didn't need to do that. I'm supplying both switches from the same circuit. A1 is for lights, B1 is for the exhaust fan. I'm feeding them from the same circuit.

I did the 14/3 to the ceiling box so I could control the light and fan individually

SVreX wrote: The lighting loads are fixed. He's not gonna pull 20A through the 14 gauge wire. Unless, of course, he puts in a 2400w light bulb!

Exactly... and I don't plan on getting a suntan while showering :)

The 12/2 is coming off a 20A breaker. From that box, the 14 ga stuff supplies three very small draws: about 2A total for lighting and 2A total for the fan. Not to mention those draws are divided among three conductors. Those conductors will see 2A max for their daily duties, which leaves a surplus for the 15A GFCI plug.

I honestly was going to run 14/2 to supply that box when I was originally planning it, but then somebody put an ad on CL for 250' of 12/2 on a spool for $20 and I snagged it. I also got 100' of 10/2 for $25. I'm slowly replacing all the ancient wiring in this 1937 house - one piece at a time

Seriously... this house was built in 1937 by the same exact family that I bought it from. Nothing had been updated. The whole house had 2-prong plugs, there was about 50' of actual lead pipe being used as gas line, and most of the plumbing was still iron pipe. Nothing like opening a faucet for a drink and getting rust-water.

You should never mix wire sizes like that. The 14 gauge wire is now your fuse with it being fused at 20 amps. Not a good idea. I understand that you won't go over the 20 amp fuse rating now, but what about the next guy who buys the house and decides to run a 14 gauge cable off of that circuit to run something else? Now he is extending a circuit that is rated at 20 amps but is running 15 amp wire. You see where this gets tricky right? Change that wire to 12/3 or change the breaker, you are violating code the way you are now. Not to mention fault currents which will indeed pull way more than 20 amps. Change The Wire, or the Breaker!!!!!! Or don't listen to the professional. No inspector in this country would allow this setup.

Hmmm...

Maybe in YOUR very small part of the country, but everywhere I've worked (18 states) would have no problem with it.

You understand that the 14 gauge is at the TAIL end of the circuit, right? It is therefore not the fuse.

And you understand that it is ONLY being used for lighting, right?

It can't be added on to.

Lighting circuits are run all the time with 14 gauge.

Just double checked with our staff electrician- he agrees with me.

I see nothing wrong with it.

Ever check the wire gauge inside many residential light fixtures? It is frequently like 18 gauge.

14 Gauge is fine for lighting, but you shouldn't back it with a 20 breaker. I don't have a problem with the breaker or the fuse independantly but mixed I do. It is not legal in my state and I doubt it is in any other. It doesn't matter where it is in the circuit(end or middle) fault currents happen wherever they want,and I want the fuse/breaker to do its job not the wire melting.

SVreX wrote: You understand that the 14 gauge is at the TAIL end of the circuit, right? It is therefore not the fuse.

I am not sure right or wrong, but it can very easly be made into a fuse.. if you drove a nail through the 14 gauge wire, in thoery the wire would burn up before 20 amps is hit to trip the braker.. so you would be overloading that wire at that point, and from all the crazy hoops I have gone through in the past with NEC codes I would be amazed that they allowed it...

Nail in the wire? Do mean dead shorted?

That's a different animal. That's not overloaded, that's shorted. And 12 gauge wire will short just as easily as 14 gauge wire.

Mazdax605 wrote: 14 Gauge is fine for lighting, but you shouldn't back it with a 20 breaker. I don't have a problem with the breaker or the fuse independantly but mixed I do. It is not legal in my state and I doubt it is in any other. It doesn't matter where it is in the circuit(end or middle) fault currents happen wherever they want,and I want the fuse/breaker to do its job not the wire melting.

This is correct - per the NEC, 14 awg wire inside the walls is not allowed on a 20 amp circuit, doesn't matter what it is used for. The size of the wiring inside the light fixture itself is a different thing, it's part of a UL approved device.

I'm sorry- still have to disagree.

Per the 2005 National Electrical Code, it is permissible to tap into existing 20 amp circuits with 14 ga wire. HOWEVER, the complete circuit cannot exceed 1920 watts, which is the maximum for a 120 volt 20 amp circuit. Normal convenience receptacles are rated at 150 watts each. The lighting should be calculated at the maximum wattage rating for the fixtures, not the bulb wattage. The fixture will have a label stating the maximum wattage. The 14 gauge section cannot exceed 1440 watts.

Granted, there are likely plenty of electricians and inspectors who take shortcuts and simply say 20A for 12 gauge, 15A for 14 gauge. But the LOAD is the determining factor according to the NEC.

Assuming the lighting load is calculated properly, how are you going to overload a 20A breaker with 1440 watts of lighting load? How are you going to overload the wire? When are you going to be able to increase the load on the wire to exceed 1440 watts?

The only way to overload the wire is to overload the fixture. If you put 100w bulbs in fixtures rated for only 60w, you could overload the wires. But that doesn't really matter, because you are risking a fire in several other ways by overloading the fixture. The illegal issue would be the 100w bulbs, not the wire size.

Can you provide a reference to the article in the NEC?

I was just looking for my NEC book and can't find it right now. I'll work on it tomorrow.

Can you provide the reference you are referring to prohibiting 14 gauge in the walls on a 20A?

Big old honkin ceiling fan, Goin slow, all night.

Picture it this way...

Let's say we have 1 circuit. 12/2 wiring, 20A breaker, only 1 duplex outlet.

Good so far, right?

Now, let's plug in a desk lamp. 25w bulb, UL-listed fixture, 16 gauge cord. (rated to carry 13A, up to 1560 watts). Good so far, right?

Now lets plug a hair dryer into the SAME duplex plug. Since women don't usually like the wimpy ones, we'll assume a Revlon Style. Average unit available from WalMart. 1875 watts.

According to the logic presented here, our poor lamp cord wire is about to burst into flames, because the potential load on the circuit is 1900 watts, which clearly exceeds the limits of the 16 gauge lamp cord (1560w).

But it ain't gonna happen. Nothing is overloaded. The lamp cord is only carrying 25 watts, the hair dryer cord is carrying 1875 watts, and the 20A circuit is carrying 1900 watts (rated for 1920 watts).

Whats a watt?