Double Insulated radio giving shocks?

[Dave Evans]

I have a background in basic electrical work but no formal qualifications other than a training course and 15 years as a Hoover engineer (washing machines).

In my 30 year experience I have encountered many item that when touched, (particularly when lightly rubbing the back of your finger over the item) I can feel a strong tingling. I realise this is because there's no earth and have also read that in some cases this is normal, but is it OK if the item is double insulated?

But is it acceptable that the 'fault' will light up a mains testing screwdriver?

I have Googled for this many times, and seen different conflicting answers. Does anyone have an explanation regards safety to use?

My latest item is a brand new small DAB/FM radio with aerial. When plugged in, the aerial will light my mains testing screwdriver. This still happens even with the power button turned off!

Any advice appreciated. Dave

 

[Dave Evans]

Thanks for your helpful reply Sparkdog. Seems like a good authoritive reply to me.
I did a 500v insulation test Live to Aerial = infinity.
Out of interest I then put a voltmeter between the aerial and earth (at wall socket) = reading of around 10v.

It's this reading that mistifies me. Is this the sort of voltage you suggest is caused by the capacitance between the double insulation and the metal aerial? If so, then at last I know what's going on.........

Hoping you spot this message.

Much appreciated, Dave

 

[Wotsit]

From what i remember about radios from my avionics days you normally have one or two reinsertion oscillators in a superhetrodine receiver, you may be picking up a voltage from one of theese.

 

[Graeme Harrold]

Thanks for your helpful reply Sparkdog. Seems like a good authoritive reply to me.
I did a 500v insulation test Live to Aerial = infinity.
Out of interest I then put a voltmeter between the aerial and earth (at wall socket) = reading of around 10v.

It's this reading that mistifies me. Is this the sort of voltage you suggest is caused by the capacitance between the double insulation and the metal aerial? If so, then at last I know what's going on.........

Hoping you spot this message.

Much appreciated, Dave

Was that not a bit of a brave test on a delicate electronic device?

 

[sparkdog]

I would say the 10 volts is due to capacitance effect and as modern multimeters draw practically no current you would get that sort of reading.I believe some equipment even has a very small value capacitor connected between mains and the metalwork so that it is not "floating" and can act as a radio frequency screen.There was an article in the Television magazine a while ago about this and possible hazards to aerial riggers from double insulated satellite boxes.