Re: OT: Housing Voltage in an Autotransformer

Frank DuVal

Did you use the Fluke for this voltage measurement? Try shunting the red and black leads with a 10 to 100 K resistor to remove "ghost" voltage. I see this all the time using a Fluke in house/commercial wiring. Just capacitance coupling. If with resistor shunt, the voltage remains,  then hmm.....

Frank DuVal


On 5/20/2022 9:48 PM, n4buq wrote:
Please pardon the OT but I don't know where else to turn except to groups like this one for some things.

I have an older Powerstat 116 that I've refurbished (mostly cosmetic but have rewired it as well). This one of the models with just a two-wire plug and I decided to keep it original.

When I powered it up, I decided to check voltages in/around the housing just to make sure nothing was leaking through to the frame. To my surprise, when I checked between neutral and the frame, depending on where I test, I'm getting some significant voltages there. From neutral to the main frame, I'm getting 50VAC which is a bit alarming to me.

With power disconnected, I checked resistance between the frame and neutral and it shows infinity with a Fluke DMM so I don't know why there would be voltage on the frame.

The frame for this model is cast aluminum(?) with a flat, disk-like base where the windings sit on an insulated disk and a conical inside that rises up inside the windings. Is it possible that what I'm seeing is just an induced voltage from the windings? If not, I just don't see where/why there's voltage like that on the frame.

(If there's a more appropriate forum to ask this, please let me know.)

Barry - N4BUQ

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