wrote:
I have seen many "newer" (15 years old or so) where the power internally
is derived from inverters right off the AC line.
Maybe I didn't stress this clearly enough before when I said
it, or maybe everyone missed it in the OP's original post :
( as I said before ) : " The thing that tells me most of all
that you need an electrician is not so much the TV and AV equipment,
but THE OLD FLOOR STANDING KITCEN MIXER WITH 30 V TO GROUND ON THE
CHASSIS".
Assuming this case and the mixer works fine (and has NO internal leakage faults).
Most mixers are two wire devices. That means the mixer has power. If that's the
case, i see two possibilities. either the hot and ground are reversed and the
mixer uses a polarized plug, or the ground on the receptacles (which is NOT used on
a two wire appliance) is NOT grounded back at the service entrance.
And the op is trying to use this ground which is not really hooked
up to anything for his tests. Now, either of these should be
an electrician issue. Maybe the house was a older house and
was upgraded from two pin to three pin sockets without actually
putting in and connecting the ground wire. It would not be the first time this has
happened. I think you can legally do this in some retrofit cases by using a 3 pin
GFI outlet with no separate ground wire back to the service panel.
Bob
This takes all the stuff about satellite dishes and mast
amplifiers getting power off the co-ax, and amplifying TV signals, and
all that other stuff, OFF THE TABLE.
In many cases the, so
called chassis voltage (chassis "ground"), ends up being something other
than 0 volts. I have seen it to be 1/2 the line voltage. The tuner
input (the 75 ohm F connector) is capacitively coupled to this internal
chassis non-0 volt-"ground". It is a very small capacitor as it only
has to pass high frequency TV signals in the MHz range. However, with a
high impedance meter, one will read some of the 60Hz line through that
capacitor. As others have stated, with a old meter, i.e. 20000
ohms/volt, you probably won't see the voltage. I would, however, make
sure there is not a fault condition.
'Not being able to see it because an old meter is less
accurate' doesn't give me much comfort.
Accuracy has nothing to do with it. Its the input IMPEDANCE of the
volt meter. A digital fluke has a typical input z or 10M ohm or so.
It can do this because it has a very high impedance OP amp buffer
on the input side.
http://www.alfaelectronics.com/FLUKE70.htm
That kind of high z input will allow a phantom voltage to read.
so it has NOTHING to do with accuracy, and every thing to do
with the load the meter puts on what is being measured.
Older analog meter have a mid level impedance. from 1000
ohms to 50K or so. Depends on the model. Most have no
input buffer amps (Older VTVM excepted), so there input
impedance is a combinations of the meter movement and the
voltage divider resistors used for the voltage ranges.
This mid level impedance is enough of a load to make these phantom voltages
disappear. Phantom voltages have voltage potential, but
little current drive potential. A phantom voltage in black box form
would be a voltage source with a VERY high resistor in series with
the voltage source. So it cannot drive much current into a load.
This phantom voltage is like getting shocked off the carpet by static
electricity. The voltage might be there but its not enough to cause any harm.
Bob
Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
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