On 3/30/2015 2:52 PM, Cursitor Doom wrote:
Hi all,

Well, I picked up a 500VA mains isolation transformer today: 240v in;
240v out. It's not brand new so I thought I'd best check it over. I
hooked up live and neutral to the two connectors on the primary side of
it, and two probes from a voltmeter on the secondary.
Without anything else attached and no current drawn yet, I applied the
tip of a neon screwdriver to the four connections with the following
results:

Primary live connection: strong yellow light from the neon tester

Primary neutral connection: no response from the neon tester

2x Secondary connections: both equally light up the tester by about half
as much as the live primary did.

I was under the impression I would see no response at all from the neon
tester on the secondary side since it's supposedly floating; yet I *did*
get a reaction of sorts from the tester.
What's going on here? Is the transformer faulty?

cheers,
cd.

You chose your moniker well.
You have analysis paralysis.

You have the ability to use absolutely the worst, least precise,
tool to make a measurement under conditions outside the normal
specification range of the devices, then fret over the result.

Measure the AC current between the output and ground with
a real AC current meter. Put a resistor in series with it to limit
the current justincase.

It would not be unusual to measure lethal currents for the worst-case
connections to your body and ground. More to fret over.

Working on line-attached stuff is very risky.
There is no such thing as "floating". There are always AC paths.
When I do it, I drag out the TEKTRONIX A6902a.
Depending on the voltages involved and what I'm doing, I might
also use an isolation transformer.
A GFI in the mix is a good idea.

I like caution, but you could have fixed the scope by inspecting
the schematic in less time than this thread has consumed.