pfm writes:

On Dec 18, 3:19*pm, (GregS) wrote:
In article , pfm wrote:

I was working on an CRT TV using an isolating transformer. I happened
to measure the voltage between the chassis 'dag' and a nearby metal
fixture and was surprised to find 75Vac. Without the transformer the
reading was 110Vac.

Something is wrong, right?

BobH

You shold be able to trace it out. I'm glad you said isolation transformer
rather than isolation transformer. You *want ground isolation because the primary
is referenced to ground. You can check out some resistances with the AC
removed.

greg

On Dec 18, 3:19*pm, (GregS) wrote:
In article , pfm wrote:

I was working on an CRT TV using an isolating transformer. I happened
to measure the voltage between the chassis 'dag' and a nearby metal
fixture and was surprised to find 75Vac. Without the transformer the
reading was 110Vac.

Something is wrong, right?

BobH

You shold be able to trace it out. I'm glad you said isolation transformer
rather than isolation transformer. You *want ground isolation because the primary
is referenced to ground. You can check out some resistances with the AC
removed.

greg

Thanks Greg but I'm not sure what you are saying. I use the terms
'isolating' and 'isolation' interchangeably. I thought the purpose of
an isolating/isolation transformer is to ensure that no potential
difference can exist between the device under test and a grounded
object such as a concrete floor or a water pipe. The risk of shock is
restricted to within the device under test.

There's always capacitive and inudctive coupling. You were probably
measuring with a high-Z DMM. Put any sort of load between the meter
probes and the voltage will go to 0. If it does not, you do have
a serious safety issue.

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