Voltage with power off

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fireryan

Senior Member
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Minnesota
I have a hanging heater with a transformer in it for low voltage control. When I shut power off to the unit I still have 75 volts across hot and neutral. When I disconnect the wire from the transformer the voltage goes away. What’s causing this?
 
fireryan said:
Fluke multimeter
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Does it have a low impedance setting?

Is supply conductors running in same conduit as other still energized conductors or within bundle of still energized non metallic sheathed cables? That will increase capacitive coupling effects if answer is yes.

I see you mentioned it goes away when disconnecting transformer lead which may lead to possible interconnection with other 24 volt controlled units and getting a backfeed 24x120 (or whatever your supply voltage is) through the transformer? If this 24 volt control is isolated and not possible to be interconnected with another source maybe there is capacitive coupling on the 24 volt circuit?
 
kwired said:
Does it have a low impedance setting?

Is supply conductors running in same conduit as other still energized conductors or within bundle of still energized non metallic sheathed cables? That will increase capacitive coupling effects if answer is yes.

I see you mentioned it goes away when disconnecting transformer lead which may lead to possible interconnection with other 24 volt controlled units and getting a backfeed 24x120 (or whatever your supply voltage is) through the transformer? If this 24 volt control is isolated and not possible to be interconnected with another source maybe there is capacitive coupling on the 24 volt circuit?
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The heater is run with another unit of the same Tstat.
 
fireryan said:
The heater is run with another unit of the same Tstat.
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Unless it is a multi-pole switching Tstat, I'd say is a good chance you have backfeed from interconnection of the 24 volt control circuits. That chance is even higher if the 24 volt secondary is grounded in both units as the EGC will connect both grounded secondary conductors together, even though one unit is "off" it can still get 24 volt from the other unit.
 
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