Electric Shock

[bigduvid]

I had a peculiar situation yesterday. The house was built in the 30's - 40's. It has knob and tube wiring, wood lath-plaster walls.

The customer complaint was that when turning on the kitchen light, they received a shock. We pulled the switch apart and found that the system switched the hot's, When the light switch was off, and we touched the box with a two wire tester, it tester light glowed lightly, an indication of leaking electricity. There was continuity between the hot wire and the box. When turning on the switch, the continuity disappeared.

We confirmed another switch on the same circuit.

There were no bare wires touching the box. Any ideas what might be the cause or what we should be looking at?

 

[Sierrasparky]

I had a peculiar situation yesterday. The house was built in the 30's - 40's. It has knob and tube wiring, wood lath-plaster walls.

The customer complaint was that when turning on the kitchen light, they received a shock. We pulled the switch apart and found that the system switched the hot's, When the light switch was off, and we touched the box with a two wire tester, it tester light glowed lightly, an indication of leaking electricity. There was continuity between the hot wire and the box. When turning on the switch, the continuity disappeared.

We confirmed another switch on the same circuit.

There were no bare wires touching the box. Any ideas what might be the cause or what we should be looking at?

Are you sure there is no metal lath?

 

[bigduvid]

Yes, it is wood lath around the two switches in question. This no wood lath in these areas. The thought occurred to me that the hot conductor is pinched by the clamp in the box. But in twp locations? And, why after so many years?

 

[yankj]

Have you checked the neutral and ground? Check voltage with a meter.

 

[bigduvid]

The switch box does not have a neutral or ground. The box contalins a hot and leg.

 

[the blur]

leaking switch.

 

[bigduvid]

I disconnected the switch and still had continuity netween the hot and the box. However, when connected to the switch, and I turned on the switch, the continuity disappeared and the small reading also disappeared.

Any other thoughts.

 

[handy10]

Yes, it is wood lath around the two switches in question. This no wood lath in these areas. The thought occurred to me that the hot conductor is pinched by the clamp in the box. But in twp locations? And, why after so many years?

I believe that you have named the problem. When the switch is open or removed, you have a path to ground through a very high resistance. When the switch is closed you have a rather low resistance to ground through the device resulting in much less current flowing through the high resistance path. Why after so many years? Perhaps the boxes wiggle a small amount and have finally worn down the insulation.

 

[Sierrasparky]

Try a analog meter