Shock from switch plate

[scouterbob]

Hi:
My old house, 1914, has much modified / upgraded electrical systems.
The circuit in question is a long run of K & T serving 5 cieling fixtures and 3 baseboard outlets on 3 floors.
The switch in question controls the basement light. The switch was added sometime to avoid using a pull chain in the dark.
It had a metal cover plate.
I got a small shock the other day.
A friend, knowledgable but not licenced, checked it out with a meter and found 56V with the switch off and 28V with it on.
This was solved by disconnecting a ground wire in the box, which disabled the one switch and light.
The wire at the breaker panel is modern c/w ground but the tie in to K & T is hidden somewhere. The ceiling is finished.

Any thoughts?

Regards,
Bob

[HayZee518]

the earth ground wire shouldn't have any current on it. if it does then there is a high resistance path to it from an appliance or fixture. a motor could cause this through its field coil shorting out to ground. A fixture it is highly unlikely because the center contact and the screw shell is separated by at least a quarter inch of air or insulation inside the lamp base. Traditionally knob and tube doesn't have and never needed an earth ground path. It was typically run with the hot on one side of a joist and the neutral run on the other side on porcelain knobs. the tube part came when there was a change in direction for the jute covered wire through a joist or downward into a wall space. Older switches were all porcelain with exposed switch parts and an insulated toggle. It could be here that you are getting your hot connected to the switch plate through the yoke.

[scouterbob]

Hi again:

Thanks for the quick answer!

The switch at issue is a modern design, (although we do have some of the cool old style push buttons elsewhere.)

Unless there is something really hidden, there aren't any motors etc. on this circuit, just lamps and alarm clocks. I threw the breaker and no heavy duty stuff went off.

What is the significance of the voltage drop, 112V to 56V to 28V?
My friend had never seen anything like it.
Why the ratio of 1 to 1/2 to 1/4? Can't be coincidental.

Anyway, with the switch disabled and no sign of other misfunction are we safe?

I'm planning on rewiring the basement lights and switch from a proven new service box but leaving lights and outlets on the 1st and 2nd floors as is K & T.

Reasonable plan?

Thanks again,
Bob

[HayZee518]

what you find a lot of times on knob n tube is cold solder joints. wherever there is a tap off, the tap is just wound around the lead wire, soldered and taped with rubber and friction tape. over time from heating on the branch circuit the solder melts and re-solidifies forming a high resistance cold solder joint. sometimes there isn't any solder at all but that joint is oxidized and forms the high resistance joint. the wire used was a tinned copper type. rarely have I seen bare true copper its always tinned copper. for some odd reason the neutral is always affected. check where your romex connects to the knob n tube. it'll be in the open somewhere in your basement. oh yeah, that rubber covered jute fiber wire, the rubber deteriorates and the jute crumbles off exposing the wire. be very careful when you remove receptacles and fixtures from their boxes and ceiling boxes respectively. the ceiling boxes are cast iron with a cast iron clamp. older fixtures were fastened to the center stud of the box with something called a hickey. the fixture wires were also rubber covered jute fiber. like chandeliers and wall sconces. all splices were just wrapped, soldered and taped. modern soldering uses rosin type paste. older wiring used acid flux. [very bad for copper]

[scouterbob]

Hi HayZee518:

Thank you very much for the extremely useful advice you've given to me and many others in the past. You're the best!

I'm calling in a pro to assess the total system in my home.

Thanks,
Bob