Using acoustic AC detector

[Robbox]

I just bought one to replace a neon screwdriver, much safer!

How are these supposed to work. Do they detect AC anywhere close to an AC wire? When I changed a single to a double and turned off the relevant circuit, it still went off. Could it be there was a cable in the vicinity that was hidden?

 

[Harry Bloomfield]

What type / model is it? A photo might help.

Some are combined AC detectors and cable/ metal detectors. If set for AC (live wire) and the circuit is dead, it should not trigger, though keep in mind some are over sensitive and there is an AC field from the wiring anyway. The principle of operation is to detect the AC field.

 

[bernardgreen]

Are you sure it is

much safer!

.

Some of these device detect the magnetic field created by current flowing in the wire. If the wire is Live ( voltage 230v ) but there is no current flowing along the wire then there will be no magnetic field and hence the indicator will not indicate that the wire is Live and potentially lethal if touched.

Other devices work by detecting ac voltage relying on capacitive coupling between the Live wire and the tip of the tester. These can also give false indication and hence are not to be relied on if you want to avoid an electric shock.

Buy and learn to safely use a two prong tester such as THIS

 

[Taylortwocities]

Trying to identify live circuits using other than a two probe voltage tester (tested as functional using a proving unit) is as useful as having an ashtray on a motorcycle.

 

[Harry Bloomfield]

Trying to identify live circuits using other than a two probe voltage tester (tested as functional using a proving unit) is as useful as having an ashtray on a motorcycle.

Not quite, they are invaluable for none invasive, no risk testing. I agree they shouldn't be absolutely relied upon, with verifying with something more capable such as you describe.

 

[Robbox]

What type / model is it? A photo might help.

Some are combined AC detectors and cable/ metal detectors. If set for AC (live wire) and the circuit is dead, it should not trigger, though keep in mind some are over sensitive and there is an AC field from the wiring anyway. The principle of operation is to detect the AC field.

this one:
https://www.toolstation.com/tis-voltage-detector/p97153

 

[SFK]

For a second had me scratching my head about how it uses "acustic and optical detection" until I realised that it meant its output is "noise and light "when it detects a voltage.

As others have said, this is not a failsafe replacement and this is highlighted in the instructions from a Fluke version:

https://www.fluke.com/en-gb/product/electrical-testing/basic-testers/fluke-1ac-ii#
Test on a known live source within the rated ac voltage range of the product,
both before and after use to ensure unit is in good working condition.
● When using the Tester, if tip does not glow, voltage could still be present.
The Tester indicates active voltage in the presence of electrostatic fields of
sufficient strength generated from the source (MAINS) voltage. If the field
strength is low, the Tester may not provide indication of live voltages. Lack of
an indication occurs if the Tester is unable to sense the presence of voltage
which may be influenced by several factors including, but not limited to:
● Shielded wire/cables
● Thickness and type of insulation
● Distance from the voltage source
● Fully-isolated users that prevent an effective ground
● Receptacles in recessed sockets

 

[Harry Bloomfield]

That is a straight forward live cable detector. It should only trigger in quite close proximity to a live cable, less than an inch or so. You can check it is operational, by rubbing it lightly on your bare forearm. Given practise with the stick, you should be able to use it to find which side the live is, is a flat twin and earth cable and trace where a neutral has been broken or lost, without opening up joint boxes, plugs, or appliances.

For instance, I managed to nick my hedge trimmer's cable a few of weeks ago - I couldn't immediately spot where I had nicked the flex. I was able with my Fluke voltstick to follow the flex end to end, to find the nick and break in the neutral. Between hedge trimmer and the break in the neutral, the voltstick triggered indicating live all the way around the circumference of the flex. Between the break in the neutral and the plug, the voltstick only triggered around part of the circumference.

You can screen it between the tips of your fingers, to make it less sensitive/ more accurately find live cables. It will probably be sensitive enough to detect live cables buried under plaster, providing they are not covered by metal channelling. They do not work on any cable surround by metal, such as a steel armoured cable or a a pyro.

Best advice is to practice using it, until you get the hang of what they can do.

 

[Harry Bloomfield]

Thanks SFK. You can never be absolutely certain a volt stick is telling the absolute truth, they are just a quick, simple test. If they don't light up, it is no guarantee that a cable is dead, you can however be a little more certain that if it lights up a cable is live.

 

[bernardgreen]

Best advice is to practice using it, until you get the hang of what they can do.

Best advice is to throw it in the bin BEFORE you get the hang that it can provide fatally inaccurate results.

 

[Harry Bloomfield]

Best advice is to throw it in the bin BEFORE you get the hang that it can provide fatally inaccurate results.

They are a brilliant, none contact bit of test kit. The first bit of test kit I reach for when dealing with any issue.