How does this electrical tester work?

[mike42]

When in single pole mode? It has a plastic case so surely there is no way for a circuit to complete as a screwdriver tester would when you touch the metal cap.

I should add I'm extremely pleased with it and should have got one years ago instead relying on multimeters or worse those dodgy screwdriver types.

https://www.amazon.co.uk/dp/B004NU2TM0?ref_=pe_27063361_487360311_302_E_DDE_dt_1

 

[ericmark]

I have this tester today, and yes it means life is so much easier, non contact volts and amps with latter AC and DC, but how new is it? The buying for just £35 yes, but the technology has been there for years.

I had a matindale tester with a bulb years ago. OK did not have a proving unit, but they have been around for years, before the take over of Hong Kong I was using a tester like you show in the tunnels which I had filled with re-enterable compound to stop water ingress. However it cost a bit more, likely it was $HK 300, Oh that's less than you show at 11 HK$ to the £.

 

[JohnW2]

When in single pole mode? It has a plastic case so surely there is no way for a circuit to complete as a screwdriver tester would when you touch the metal cap.

If you're holding the plastic case, there will be capacitive coupling (through the plastic) to your body, even though you are not touching any metal.

If you play with a neon screwdriver, you may well find that, if its end is touch something live, it will 'light up' even if you hold a bit of the plastic body near the end (touching nothing metal), or maybe even if you put your had close to the metal cap.

Kind Regards John

 

[Harry Bloomfield]

When in single pole mode?

I'm not seeing any mention of a single pole mode, only dual pole, however - Single pole usually relies upon capacitive coupling, between user a general earth, or between probe and the surrounding air.

 

[mike42]

I'm not seeing any mention of a single pole mode, only dual pole, however - Single pole usually relies upon capacitive coupling, between user a general earth, or between probe and the surrounding air.

Yes if you touch with one probe only (the main one) a 240v terminal, it will beep and flash.

 

[mike42]

If you're holding the plastic case, there will be capacitive coupling (through the plastic) to your body, even though you are not touching any metal.

If you play with a neon screwdriver, you may well find that, if its end is touch something live, it will 'light up' even if you hold a bit of the plastic body near the end (touching nothing metal), or maybe even if you put your had close to the metal cap.

Kind Regards John

Thanks a lot for giving such a good answer. Could I ask though, do you think that makes it as "dangerous" as the cheap screwdriver types since they work the same way ?

 

[JohnW2]

Thanks a lot for giving such a good answer. Could I ask though, do you think that makes it as "dangerous" as the cheap screwdriver types since they work the same way ?

'Voltage', by definition, only has meaning in terms of the 'voltage difference' ('potential difference') between two points.

That being the case, there's only one way in which a 'single pole voltage tester' can work - namely by detecting the difference in voltage between a point and 'earth', by there being a 'connection' through a human being's body from what is effectively the 'other pole' of the tester to 'earth'. Some of that connection is inevitably by capacitive coupling (between the person's body and 'the earth'), the rest of it being by 'direct touching' in the case of a neon screwdriver or by another bit of 'capacitive coupling' (between the person's body and the device) in the case of a device like yours.

Your device is therefore conceptually the same as a neon test screwdriver. If there is any difference, the neon screwdriver is perhaps slightly 'better' since at least some of the path to earth is then 'by direct contact' whereas with your tester it is entirely capacitive.

As for "dangerous", the issue with any single-pole voltage tester is that the capacitive coupling between a person's body and earth is an iffy and uncertain/unreliable/variable business - such that failure of the device to 'detect voltage' cannot be taken as a guarantee that 'a voltage' is not actually present - and that it true of any 'single-pole yester, whether a neon screwdriver or a device such as yours. However, as above, if there is a difference, the neon screwdrivers may be slightly less iffy in that respect.

At least in my opinion, single-pole testers (of any sort) have their place and uses in the hands of someone who understands them and their limitations but the crucial thing to understand it they must not be used when it is important to be able to reliably detect the absence of voltage (i.e. that something 'is not live').

Kind Regards, John

 

[ericmark]

The explanation @JohnW2 seems good, however my non contact volt tester seen here is detecting volts with my hand no where near it. You can see all four bars showing, and it was beeping and the red LED flashing rapidly. I know the device uses the hall effect to measure DC current, and on DC it needs zeroing, and slight movement can alter reading, so although measures in 1 mA increments, I would only take it as an indication, the AC current range however is far more stable, again 1 mA increments.

I really have no idea what is in the jaws, or what voltage it will detect, never tried on low voltage DC or tested on low voltage AC, would be interesting to try at work on reduced low voltage and see if it works.

I had thought the volt pens used a reed switch, however not sure what the sensor is, and in all cases not sure what they will do with DC, I suppose easy enough to test, I could hold close to the solar panel leads, they are around 250 volt DC.

But the volt stick is non contact, the neon screw driver makes contact the metal clip needs to be touched with your hand, and the screwdriver tip needs to touch line, and there is a resistor to limit the current, the worry is if the resistor is shorted out with dirt etc, when stored in a tool box.

I think the neon tester is a very good second string to ones bow, for detecting borrowed neutrals, the clamp on should detect current if clamped around a neutral wire carrying current, but often not room enough to get the jaws in, seeing the neon in the screwdriver light when disconnecting a neutral can save one from a nasty shock.

But my meter does allow one to use leads as well, so the non contact voltage is good for testing a FCU before removing the 3.5 mm screws, but once the FCU is dangling on wires I would retest with leads to show really dead. Did not fit leads in today's test as they may act as aerials, and wanted to see if it can detect voltage without having the leads in place.

I don't know how the testers work, however I do know if a pen detector is dropped, they can stop working, so testing it works before and after is important, I have seen them rubbed on clothing to test, but I am weary as to if this test is any good.

 

[SFK]

 

[JohnW2]

The explanation @JohnW2 seems good, however my non contact volt tester seen here is detecting volts with my hand no where near it.

That's not particularly surprising.

There obviously has to be an 'electrical connection' between 'the second pole' of the device and earth, otherwise there is no PD for it to detect.

That connection will be at least partially by capacitive coupling (augmented by some 'actual contact' in the case of a neon screwdriver etc.), but there is no reason why it cannot be entirely by capacitive coupling (i.e. directly from the device to earth, without an intervening human body).

However, I would imagine that the capacitive coupling would be even more 'iffy'/unreliable when there was not also a ('fairly substantial') human body in the equation.

Kind Regards, John

 

[ericmark]

In my case, the contactless test is before covers are removed, once removed, I use wires.

They have there place, and to date it has worked well. But would not rely on them, always test at least twice.

 

[JohnW2]

In my case, the contactless test is before covers are removed, once removed, I use wires.

Sure,if one can use two poles, then one should.

They have there place, and to date it has worked well. But would not rely on them, always test at least twice.

Agreed- as I've said. However, no-one should ever interpret what you've written as meaning that 'testing twice' (or even 'testing 10 times') makes it any more acceptable (or safe) to use a single-pole tester to confirm the absence of any voltage.

Kind Regards, John