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Kent Monroe
 
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Default Strange not-quite-240 high-voltage smoke problem... short? circuit breaker?

Hi all,

I have a puzzler and need help. I'm getting some very strange high
voltages, high neutral-ground voltages, and smoke! I'm not sure if
I've got a bad breaker, or a wall short, mis-wiring, or a broken
ground, or ???


My sister-in-law's condo has a 2-pole 20Amp Sylvania circuit breaker
circuit which provides two different phases of 120V to the following:

1st 120V pole: Garbage disposal, powered on by a wall switch.
2nd 120V pole: Dishwasher

One of the above also powers a regular wall socket but I didn't check
which pole (probably the 1st). The wiring for both poles is pretty much
behind the sink, likely routed next to each other from the main box.

The disposal and dishwasher have worked fine in the past, but all
of a sudden, both stopped working. As the dishwasher was old and had a
broken latch too, she decided to buy a new dishwasher, and nice brother-
in-law that I am, I agreed to install it for her for free (tight budget).

I noticed something strange with the voltage meter from the start,
which is that I still had some residual voltage on either circuit until
I turned BOTH circuit breakers off. For example:

With nothing connected to either circuit (which turns out to matter but
shouldn't), I measured voltages of the wires at the appliances:

1st pole (disposal) breaker OFF, 2nd pole (dishwasher) breaker ON:
1st pole: black-neutral ~12V ; black-ground ~13V ; ground-neutral ~1V
2nd pole: normal 120V (black-neutral ~121V ; black-ground 123V)

1st pole breaker ON, 2nd pole breaker OFF:
1st pole: normal 120V (black-neutral ~121V ; black-ground 123V)
2nd pole: black-neutral ~15V ; black-ground ~16V ; ground-neutral ~2V


So then, I wired up the dishwasher, turned on the 2nd pole and... nothing.
The dishwasher didn't work. It didn't matter that I had just measured 120V
before connecting it.

Next I plugged in the disposal, turned on the 1st pole, then the wall switch
and then... the disposal ran like a bat-out-of-hell! Then SMOKE appeared
at both the disposal, AND from the bottom of the dishwasher (which wasn't
even running) !!!

Fortunately, when I tested both the disposal and the dishwasher on a different
wall-plug circuit, both still worked fine. Nothing smoked, and the disposal
motor was clearly running normal, slower than before.


One more test: With the dishwasher connected (2nd pole circuit) I measured
voltages at the (1st pole) disposal wall plug (without the disposal
connected, since that makes smoke), and I got the following abnormal
voltages:

With both 1st pole and 2nd pole breakers ON:

2nd pole: black-neutral 206V!!! ; black-ground 123V ; neutral-ground 85V!!!


With the 1st pole breaker ON, and 2nd pole breaker OFF, it seems "normal":

2nd pole: black-neutral 121V ; black-ground 123V ; neutral-ground 3V


With the 1st pole breaker OFF, and the 2nd pole breaker ON, it's weird:

2nd pole: black-neutral 47V! ; black-ground 33V! ; neutral-ground 83V!



Oh, and by the way, during the many measurements of voltages, I got careless
and managed to arc the wires at both circuits with my voltmeter probe
(which lost it's nice brand new pointy tip :-O ). It neither case
did either 20A breaker trip. Maybe it didn't exceed 20A, but I was a
bit suprised it didn't trip the breaker).


What the heck is going on? How come the dishwasher won't work with JUST
it's own breaker turned on, and with 121V no-load voltage measured?

How come I get smoke and strange high-voltages with both appliances
connected and both breakers on, as soon as I turn on the disposal?


Should I just replace the breaker first, and if that doesn't fix it,
call an electrician? Or is replacing the breaker a waste of time
and money?


Thanks in advance for any help,
Kent