Residual voltage question

[tiernsee]

I wonder if any electrical experts can offer some advice? My husband has acquired a mains voltage tester and has been going round the house sticking it on metal objects, like the gas fire, a radiator, a metal ceiling light fitting and the screws on a wall light switch. Some of them are registering a residual voltage of 12V and he now seems convinced there is an issue with the earth.

Please could any experts out there suggest any rational explanations for this and is he right to be worried?

Many thanks

 

[deadshort]

Yes, bin it ! or use it to unscrew screws that's all its good for

Kind regards,

DS

 

[stillp]

What is this "mains voltage tester"? Can you describe it for us?

 

[tiernsee]

Yes, it is a contact tester - a pen-type voltage tester. It has two buttons, one says "inductance breakpoint test" and the other "direct test". It looks like this one from B&Q http://www.diy.com/departments/bq-pen-type-voltage-tester/177924_BQ.prd

Thanks

 

[stillp]

Those labels on the buttons don't make sense.
I partly agree with Deadshort, except that it's no good for undoing screws either! Bin it and get a multimeter. Was there a reason why your husband acquired it and went round "testing" things with it? Have you had electrical problems in your house?

 

[Taylortwocities]

£3.38! That's got to be a quality tool. It's interesting to see that this voltage tester is able to "detect the flow of electrical current".

Mind you, your regular £10ish multimeter will probably throw up some stray voltage readings. Both items have very high impedance and will show up an induced voltage. In the real world these voltages are not there, as there is usually a load on the end.

There are tests that he could carry out if he is concerned about earthing, but a low ohm test meter is needed for that.

 

[tiernsee]

Thanks for the replies. We got it for testing voltages on a PCB in the boiler as a diagnostic tool when the boiler stopped working. We do seem to get through a lot of light bulbs, and he thinks that this could be a problem with the earth.

He got a reading of 12V from one radiator but not a different one. I suggested that as the radiator with the reading backed onto our high power cooker circuit maybe it was some induced field event?? I am not, though, an electrician and my physics schooling was many, many years ago so I really don't know!

 

[bernardgreen]

Those devices measure the voltage difference between the person holding it and the item the probe is touching. If it indicates a voltage when touching an item that is earthed then the person holding it has a potential on their body. This can happen if the person is standing close to cable that has live wires in it. Capacitive coupling induces a voltage into the person's body.

They are not accurate and in some circumstance can fail to detect a dangerous voltage.

Induced voltages can be very high but due to the very high impedance of the capacitive coupling that is creating the voltage any current taken reduces the voltage to almost zero.

 

[ban-all-sheds]

We got it for testing voltages on a PCB

It can't do that.

 

[ericmark]

Voltage often called PD or potential difference is a comparison so if one looks at two milk bottles with water in one on the floor and one on a chair the potential energy in one bottle would be greater with the one on the chair but unless you fitted a syphon tube the energy could not transfer.

Insulators can separate 1000's of volts rubbing the balloon on a jumper we can get it to stick on the ceiling where the two different voltages attract each other.

At school we used a gold leave electroscope to measure static electricity but today there are many other devices which can detect it.

Friction is the main generator be is clouds in the sky blown about by the wind or a slipping fan belt on a car these can all generate static electricity.

As humans we move and our clothing rubs together and we will produce static electricity without trying. In fact we have to go to great lengths to stop this static doing damage with earthing bands on out wrists when working with electronic components.

During the winter less moisture is held in the air and in building the humidity drops and I can see where when working on electronics you would want to test to see if there is a likely problem which could blow electronic components.

But I am at a loss to work out why anyone would want to do this in a domestic situation? Could be interesting testing a TV aerial socket I wonder how many 1000 volts it would measure specially in an electric storm?

But why one wants to record the potential of ones body to different items in the house I don't know? Clearly as one moves the bodies potential will alter so stand next to the radiator and measure then rub your arms together as if very cold then remeasure and I am sure you will get a different reading. Testing the balloon would be interesting but wonder what it's limit is.

I am sure as a child I would have found it interesting doing things to change the reading. And for most that is all it is. A child's toy. It has very little use. I must admit I would not select B&Q as a shop for children's toys I wonder what other toys they stock.

Clearly all toys can be used for useful work you should see what I can do with Meccano. James May even built a house out of Lego but I would still class them as toys.

 

[ban-all-sheds]

James May even built a house out of Lego.

And a motorbike out of Meccano, which he took round the IoM TT circuit.

 

[JohnW2]

Can anyone offer even a clue as to what "inductance breakpoint test" might be intended to mean, or relate to? On the face of it, it seems to be the best example of 'sheer nonsense' that I have seen for quite some time!

Kind Regards, John

 

[ban-all-sheds]

"Contact AC/DC voltage test: 12V to 500V. Non-contact AC voltage: LCD screen display the voltage, find phase line, ground line, firewire and breakpoint of phase line. Inductance breakpoint test: keep the tip of tester 1-5 cm from the tested electric line, if an induction marking is found on the LCD screen, the tested line is firewire. Ideal for testing household electric appliances, AC/DC cable, circuit breakers, wall sockets, junction boxes, fuses, etc. Safe to use, no need any power supply."

 

[JohnW2]

"Contact AC/DC voltage test: 12V to 500V. Non-contact AC voltage: LCD screen display the voltage, find phase line, ground line, firewire and breakpoint of phase line. Inductance breakpoint test: keep the tip of tester 1-5 cm from the tested electric line, if an induction marking is found on the LCD screen, the tested line is firewire. Ideal for testing household electric appliances, AC/DC cable, circuit breakers, wall sockets, junction boxes, fuses, etc. Safe to use, no need any power supply."

Is that English? Whatever language it is, are you able to translate it into one I understand??

Kind Regards, John

 

[ericmark]

It does firewire so will it do USB 3 as well? It's just a toy like buying a transformer