Aerial with voltage!!!

[jacko57]

Asked to split main incoming aerial,to keep exsisitng location,plus a new cable to a new consevatory.

When i dissconected the joiner (that already been joined at some time in past)from the main aerial (loft) to the cable comming out of the digibox,the one out of the box gave me a small tingle/shock ,when i put the meter on the cable it read 5 volts, remove it out of the digi box and of course no voltage.

Cant be correct can it?

 

[MasterAbacus]

What kind of digi box is / was it connected to?

If its plugged into a Sky box, then there could be voltage depending on your setup.

More info might help you out here...

 

[davelx]

Yes, quite normal/common in class II equipment for its chassis to float above earth due to filter capacitors at the mains input. The impedance is very high, so the available current is tiny and is not hazardous. The reading you get on a meter will depend on the impedance of the meter.

It'll probably light a neon screwdriver too.

 

[jacko57]

Cheers guys yes sky box then straight into tv.
it would not light my Fluke tester.but enough to not want to keep your fingers on the cable end.

So no hazard then?
cheers

 

[Adam_151]

Pretty normal for the AV equipment to do this, as already said and the standards permit it

I'm lead to beleive that where an aerial installation supplies a large amount of sets that its the norm to tie the screen of all the outgoing aerial feeds to earth at the headend via a 4mm² single back to the MET, which is what these http://www.dastv.co.uk/8_Way_Earth_Bar_133.php things are far

 

[bernardgreen]

So no hazard then?
cheers

Not really but best to check it before going up to the roof and unplug aerial lead if possible until aerial work has been completed.

It may take someone by surprise at the top of a ladder on a rainy day and they may fall of the ladder

( rain = wet roof and brickwork == enough route to earth to feel the tingle )

 

[Adam_151]

on that note, vaguley remember someone telling me about a problem that they tracked down for someone involving an RCD that tripped when it rained and turned out to be a faulty television where the isolation between the aerial and the chasis had failed, and when it rained this allowed a current to flow from aerial to terra firma!

 

[THRIPSTER]

Some systems provide power to remote aerial amplifiers via the arial co-ax; isolation betwee signal and DC power being achieved by the use of capacitors.

 

[FullPint]

Yup - what Thripster said.

It's for powering this sort of thing without having to use an additional power supply.