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nealt · 07-19-2008, 10:47 AM

My house was built before 1920. I have one three prong outlet that is on its own circuit breaker with old wiring. It stopped working after working fine for over 20 years. The circuit breaker was still on. Upon opening the outlet box I found that the case ground was connected to the outlet neutral and ground. The "white wire was not connected to anything and was wrapped with electrical tape. Using a multimeter I found that there was 56 volts across the outlet, 96 volts from hot to white wire, and 25 volts between the white wire and ground. There are no loads on this line as far as
I know. What could be going on? how can I fix it?

Yoyizit · 07-19-2008, 10:56 AM

Quote:

Originally Posted by nealt

Using a multimeter I found that there was 56 volts across the outlet, 96 volts from hot to white wire, and 25 volts between the white wire and ground. There are no loads on this line as far as
I know. What could be going on? how can I fix it?

Load down your high input impedance voltmeter with a 4w to 100w bulb using one of these
http://images.orgill.com/200x200/4186144.jpg

If the voltages don't drop to ~0v search for a bad neutral connection [one that shows >> a 3 millivolt drop across it].

If they do drop to zero, those wires are not connected to anything and the voltages are due to ~100 picofarads per foot of parasitic capacitance in the cables.

nealt · 07-19-2008, 11:06 AM

Thanks for the reply. Should I put the load across the hot and "white" wire which would seem correct or between the hot and the green wire, the way the outlet was originally wired many years ago?

Yoyizit · 07-19-2008, 11:20 AM

The bulb goes across your voltmeter leads, converting your meter into a low input impedance voltmeter.

Then any measured voltages that stay above ~0v have a low source impedance.
The source impedance of a good, correcly wired outlet measured across the short slot and the long slot should be about 1/4 ohm, per page 7 of this
http://www.idealindustries.com/media/pdfs/products/instructions/61-164-165_instructions_v4.pdf

So if an outlet measures 120v and you load it down with a hair dryer pulling 10A, the voltage should drop no more than 1/4 x 10 = ~2.5v.
You are measuring the Thevenin Equivalent Impedance.

I recommend reading the voltages between a known good ground, like a cold water pipe, and the wire to be tested.
120v that lights the bulb is almost certainly the hot wire and is supposed to be the black wire.
Then, 120v that lights the bulb between this hot wire and the others almost certainly means the others are neutral or ground.

Don't qualify for a Darwin Award!

nealt · 07-19-2008, 01:51 PM

With a load on the hot and "white" wire the voltage across the load dropped to zero. However the voltage between these wires and ground is 28 volts. Any more ideas?

Yoyizit · 07-19-2008, 02:20 PM

Quote:

Originally Posted by nealt

With a load on the hot and "white" wire the voltage across the load dropped to zero. However the voltage between these wires and ground is 28 volts. Any more ideas?

So far, so good. . .

So the voltage across hot and white drops to zero with a lamp load? This means these two wires are not connected to a "stiff" (~1/4 ohm) source, but one of them may still be.

Voltage, hot to Known-Good-Ground with lamp load =?
Voltage, white to KGG with lamp load = ?

One conductor of a 50' extension cord makes a good, long voltmeter test lead to connect to your good ground.

I find that it is sometimes difficult to get a good connection by poking a voltmeter probe into a socket so I recommend you plug in a turned-off appliance and then retract the plug just enough to contact the plug blades, 1/4" or so.

If your plugs pull out easily, you have another problem in that the spring contacts are weak, which cause high temps in the outlet and shorten motor lifetimes.

Stubbie · 07-19-2008, 03:00 PM

Jeez why don't we make this as complicated we can.....

Nealt

Take the bulb tester and forget the digital multimeter. Touch (carefully) the black wire the other black ...touch white to ground does it light the bulb?... N0....open ground or no power on the black.

Test black wire to black and white wire to white...does not light the bulb... ...open neutral or No power on the black.

Do you have voltage at the breaker terminal....?

nealt · 07-19-2008, 03:45 PM

Well I discovered that there is a hallway light on the same circuit breaker. It is working fine. Also the wiring to the circuit breaker is relatively new. So somewhere there must be a junction box. I have not been able to find it.

Stubbie · 07-19-2008, 04:27 PM

Hi Nealt

You are on the right track while you have the hallway light switch box open and the ceiling fixture you need to check the connections and find everything powered by that breaker.

When you say the wiring to the breaker box is new are you talking very recently and the outlet stopped coincidently with that work?

Also using the ground as neutral is a no-no so when you find the problem you need to get that unused white wire at the outlet connected as the neutral and the ground to the equipment ground.

BigJimmy · 07-19-2008, 04:46 PM

Quote:

Originally Posted by Stubbie

Jeez why don't we make this as complicated we can.....

A-f'ing-men!

Whenever HO's ask me about test equipment, I always tell them to get a wiggy (or just borrow mine). 99% of the time, we just need to know if we have zero, 120 or 240V or measure for continuity.

In my line of work which deals with low voltage DC signaling circuits (12 or 24/28V DC), the good guys all carry a test light which is nothing more than a 12V incandescent bulb connected to a couple of aligators. Especially when you're dealing with line circuits that can be on the order of miles in length, DVM's will lie like a rug. But a test light never does.