Are they both connected to the same earth terminal ?
Even if they are the earth screen will act as short wave antenna so will
pick up electromagnetic radiation and that's probably what your meter is
measuring if you set it on AC. Even if you hold the metal part of meters
prods one in each hand without anything else connected it will still give
you a reading.
How can you feel 4 or 5 volts through your fingers. Were they wet ?
Have you tried measuring the current ?
A volt meter has a very high internal resistance which is why it is able to
measure even very low voltages between two unconnected wires. Since the
resistance between them is huge very little current is flowing. If you use
an ammeter to measure the current it I doubt you would get any current
flowing at all.
I missed the first part of this, but here is something that happened
once that may be relevant.
One laptop. One PC, one serial cable being used (before the days of USB
etc) to transfer data between them.
One teeny spark, and blown serial ports on both..
One voltmeter of high impedance variety conncted between the PC earth
and the laptop ground shows 115v AC..
The cause? The laptop was powered via an RFI filter with a capacitor
from live and neutral to the laptop ground, with the SUPPLIED 2 WIRE
i.e. there was NO mains earth on the laptop whatsoever..and the RFI
filter bled enough current through the capacitors to cause enough of a
surge to blow some components.
Yup, had exactly that happen in an office once. We were using two PCs
eitehr side of the room, hooked up via a serial cable, and got a slight
kick from the shield of the cable on plugging it in - nett result dead
port on one PC.
The place was wired with singles in metal conduit, and used the conduit
as a CPC. It turned out that the gland on one of the the sockets
providing connection to the conduit had worked loose over the years.
Its not an overhead cable, anyway both units are in the same room so they
should share the same earth, however, one unit is a set top box
with its own power supply, so it only has two cables going to it,
live and 'earth', dunno which of the two earths it uses (earth or neutral)
same would go for the freeview dongle.
Anyway I tried measuring amps and it read nothing, volts gave 87V on
AC!! So I aint to sure what is going on, all I know is that my signal
I would also add that I detected a spark when plugging the aerial in to the
TV directly on one occasion!! TV is OK but it was rather disconcerting!!
It was audible and visable, the sort of thing which would easilly blow a
designed for small signals as in TV signals.
c. 1990 I was involved with commissioning SIS systems in betting shops.
I was called out to investigate problems at one newly refurbished and
All the monitors displayed severe hum-bars and there was a defining hum on
The satellite receiver and C-MAC decoder were located on a wallboard on one
side of the building and the monitors, text computer video distribution amp
and audio amplifier on the other.
The shop had been two separate units, (you guys are ahead of me now yes)?
The installation was using two different supply phases.
No, later than that, at the time when Extel gave way to SIS.
BT installed the satellite kit, someone else installed the cabling and we,
did the rest.
GTVR (I think they were called UKRS then) installed the TV's and
I turned up in my Granada Microcare blazer and installed the computer,
connected the whole
thing up and commissioned it.
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