mystery 29 volts

[RogBaker]

I am going to install a ceiling fan with a light kit in the master bedroom. The junction box in the ceiling has a 2-conductor wire (plug ground). I replaced this with a 14-3 wire because I want the ceiling fan and the light on the fan to have their own seperate power. I wired in the new switch and now one switch provides power to the black wire and the new switch provides power to the red wire.

Now before I installed the fan, I decided to measure the voltage on the wires. Flipping the switch to ON causes the appropriate wire to measure 122 volts from ground (and neutral). However, If one switch is OFF, and the other is ON the power wire connected to OFF switch measures 29 volts. I expected this to measure closer to zero. If I do put a load on this, it will go to zero. Is this fine/normal? What is causing this, induction? By the way, the wires that I am measuring are way longer than they need to be. I will cut them at the appropriate length when I am satisfied everything is wired correctly.

[hallerb]

bet your using a digitaL METER? its capactive coupling, digital meters are too sensitive. try a light bulb, see if it glows

[HeyBub]

Your expectations are in error.

Yes.

Alternating current. The application of current creates a magnetic field around the conductor. The changes in this magnetic field induce a current in surrounding conductors. This phenomena is called "induction." Wave a strong magnet over your voltmeter test leads and see the same thing.

Leave as much spare length as you reasonably can. Future changes.

[RogBaker]

Thanks hallerb, Yes, in fact, I used this project as an excuse to by an new digital meter. I probably still have an analog meter around somewhere. I wonder if my older digital meter will give the same reading. Thanks, I will try the bulb test.

[tnom]

It's really a function of any meters input impedance being very high. So high that induced voltage or capacvitively coupled voltage on the wire can not drain off. Just put a little load between the two wires and you'll get the true reading.

[james]

Use a cheap analog meter for this purpose because they have a built-in load.

Or use a resistor as load, something like 100K ohm.

[Don Klipstein]

This is normal. You are getting capacitive coupling. The amount of current involved is in the microamps.

- Don Klipstein ( [e-mail])

[Don Klipstein]

Chances are the analog meter will read only a few volts. I have seen open wires next to hot wires pick up enough to cause a neon test lamp to glow dimly, but fairly easily visible in a dark room. If the cable has a wire between the two coupling to each other, and the wire in between is grounded, then the wire picking up voltage will pick up less voltage and be unlikely to make a neon test lamp glow.

- Don Klipstein ( [e-mail])

[Don Klipstein]

In article , HeyBub wrote in part:

That's not the explanation here. No load is connected - so no current except leakage is flowing. There is essentially no magnetic field.

The explanation is capacitive coupling.

- Don Klipstein ( [e-mail])

[HeyBub]

Right. My bad.