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#129416 - 02/26/05 06:37 PM lost neutral
ds247 Offline
Member
Registered: 05/17/03
Posts: 18
Loc: California
I was working on a furnace which uses 120v and the control circuit uses 24v. I checked the two secondary leads on the transformer and got 0v. Then I checked the primary hot lead and the chassis and got 120v. Turns out the primary neutral had a bad connection. My question is when I checked either secondary lead (without the primary neutral connected) to the chassis i got 12v. How could I get anything when there is no current flow through the primary side of the transformer? Thanks
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#129417 - 02/26/05 08:51 PM Re: lost neutral
Trumpy Offline


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Registered: 07/05/02
Posts: 8211
Loc: SI,New Zealand
ds247,
By rights, you shouldn't have had 12V to the Chassis (unless one side of the Secondary is connected to it).
Assuming that this is a Double-wound transformer, there should only be voltage between the two secondary leads.
It sounds like there is a broken turn on the Secondary side of the transformer.
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#129418 - 02/27/05 02:46 AM Re: lost neutral
pdh Offline
Member
Registered: 01/20/05
Posts: 354
This could be capacitive coupling across the transformer and returning over the chassis to the 120v ground. Or if the neutral is broken in a way that allows it to capacitively couple with a ground wire, it could be a complete circuit through that coupling. Put a 24v load on the secondary (a pigtail socket with a 100w 120v light might do). If the former cause, the 12v may remain. If the latter cause, it should go away.
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