How do I ground a chassis with only a 2-conductor power cable?

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Hello again all,

I have a polarized, 2-conductor power cable. If I use this to power a
device that is in a metal cabinet, how do I safely ground the chassis of
the device to prevent user shock in the event of a hot short to chassis?

The use of a 3-conductor cable is impractical for my purposes, and the use
of only 2-conductor polarized cables is done all the time by manufacturers
of TVs, VCRs, and stereo equipment.

I asked a question before and received two answers which, although helpful
to some extent, did not provide me with what I need to know. So, I
decided to rephrase the question. I actually am using a plastic case for
a power supply, and I'd prefer to stick with the 2-conductor cable if at
all possible. What I'm actually trying to do is shield the power
transformer so that I can eliminate hum that is being picked up by nearby
projects inductively. I've wrapped the entire box in aluminum foil and
crimped it onto a wire in the -VDC lead, which didn't help. I've tried
attaching just the transformer case to -VDC, which of course didn't help
either. I need to somehow "ground" the transformer case, but I'm wary of
tying it directly to the neutral conductor. I know there is a way to do
this using "AC rated" capacitors, but I know nothing of what caps I need
or what to do with them. The reason I think this should work is that it
works for the VCR people -- they use chassis-grounded shielding to
separate the transformer from the electronics of the receiver/tape reader,
so this same trick should work for me. But, they somehow connected the
chassis to the line neutral through some kind of resistor-capacitor setup.
I *could* use an old computer power cable, but I would rather not destroy
something just for the exclusive purpose of bringing an earth ground to
the transformer case.

Any thoughts? Sorry for asking the question again, but I'm sure SOMEONE
out there knows what I'm doing and can help.

Thanks in advance, again...

CJ

 

I would never assume that there are NO wiring errors on hot vs
neutral. Don't connect your chassis to either of the 2 wires. Use a
3rd lead or forget it.
GG

 

I'll second that!

And add that everyone who does know what you're trying to
do will help. By telling you not to.

Ken

 

Would an isolation transformer help???.

They are used in TV workshops to work on "live" chassis..............

Regards, Gordon.

 

The screen needs to be made of a magnetic material, such as iron or
steel -that's why aluminium makes no difference, it is transparent to
magnetic fields. The material used to screen the c.r.t. of an
oscilloscope is the best. They call it, or used to call it, mu-metal.
But perhaps this was a trade name.

Why? If it screened, the screen doesn't need to be "grounded".