Non contact pen picking up current on water pipe

[Stephenmunt]

Non contact pen picking up current on my water pipes. I've turned off the boiler but it's not that. Found that it's the down stairs lighting. I'm starting out on electrics so medium to low experience. Is this a normal thing?

 

[telectrix]

you can't relyom the voltstick. you need a proper meter to masure any voltages ( usually relative to your Main Earth Terminal) on the water pipes. If in doubt call in a qualified spark as a fault if present could be dangerous.

 

[davesparks]

Non contact pens will light up if you rub them on your trousers fast enough.

It may well be a perfectly normal thing or it could be a sign of trouble, impossible to tell without some proper testing.

Also what you are detecting, if anything, will be voltage and not current. If you are just starting out it is especially important to learn what these two things are and how they relate to each other. This is fundamental knowledge that will make a lot of other theory easier to understand if you can get them right now. It's surprising how many fully qualified electricians don't actually understand what voltage and current are!

 

[Stephenmunt]

Non contact pens will light up if you rub them on your trousers fast enough.

It may well be a perfectly normal thing or it could be a sign of trouble, impossible to tell without some proper testing.

Also what you are detecting, if anything, will be voltage and not current. If you are just starting out it is especially important to learn what these two things are and how they relate to each other. This is fundamental knowledge that will make a lot of other theory easier to understand if you can get them right now. It's surprising how many fully qualified electricians don't actually understand what voltage and current are!

Thank you for your reply. To add more info my clamp meter reads AC 0.021V and on another pipe next to it it reads AC 0.010V. if this is normal how do you spot the difference in future between a fault or something normal? And also why do you get a reading for pipes? Does it have to do with the live wires around the pipes under the floor bords creating a kind of magnetic field?

Thank you

Stephen

 

[Taylortwocities]

Does it have to do with the live wires around the pipes under the floor bords creating a kind of magnetic field

This is the reason for spurious volt readings in most cases.

 

[Lucien Nunes]

Non-contact voltage detectors are versatile and useful but their behaviour is more subtle and complex than might appear at first glance. Their indications can be easily misinterpreted unless you understand about electric fields, which is perhaps why some people say they are unpredictable and useless because they don't fully grasp what the detector is telling them. As a newcomer, I'd suggest putting the non-contact detector aside for now and getting used to taking measurements with conventional test equipment. Return to it and discover its unique advantages once you are familiar and competent at using the MFT and multimeter.

my clamp meter reads AC 0.021V and on another pipe next to it it reads AC 0.010V

Voltage is always measured between two points, but you have not identified what the other point is, so the numbers are meaningless. A statement such as 'I measured 0.021V between the pipe and the main earthing terminal' conveys information. Voltages like these, down in the tens of millivolts, can be completely insignificant or moderately interesting depending on what exactly you are trying to discover.

 

[Stephenmunt]

Non-contact voltage detectors are versatile and useful but their behaviour is more subtle and complex than might appear at first glance. Their indications can be easily misinterpreted unless you understand about electric fields, which is perhaps why some people say they are unpredictable and useless because they don't fully grasp what the detector is telling them. As a newcomer, I'd suggest putting the non-contact detector aside for now and getting used to taking measurements with conventional test equipment. Return to it and discover its unique advantages once you are familiar and competent at using the MFT and multimeter.


Voltage is always measured between two points, but you have not identified what the other point is, so the numbers are meaningless. A statement such as 'I measured 0.021V between the pipe and the main earthing terminal' conveys information. Voltages like these, down in the tens of millivolts, can be completely insignificant or moderately interesting depending on what exactly you are trying to discover.

Amazing reply. Thank you very much.

 

[Taylortwocities]

Amazing reply. Thank you very much.

Further, if you use a regular multimeter: these are very high impedance and will(can) also display spurious voltages as the result of induction from wiring.
A suitable load/shunt resistor solves this issue.
Professional test equipment includes circuitry to eliminate this.

 

[Lucien Nunes]

We might have to expand on the definition of 'spurious' for the OP's benefit.

The voltage sensed e.g. on a disconnected a.k.a. floating conductor that has significant capacitive coupling to a live one, is a real voltage. It's not unknown to read 50-100V on a long 'dead' circuit lying amongst live cables. But the source impedance is very high, and hardly any current can be taken from it, maybe a few microamps. Measuring the voltage tends to change it because even the high resistance input of a multimeter loads it down, forming a voltage divider, hence the common term 'ghost voltage.' In normal electrical work so-called 'ghost voltages' are largely irrelevant. You need to understand why they occur, but they pose no threat and serve no purpose.

In electronic work however, high source impedance is not just a phenomenon to brush aside. Historically more so than now, in the days of valves, operational circuits would have such high impedances that measuring them pulled them down to a lower figure than when operating normally. The vintage electric organs that I collect have exceedingly high impedance circuits, up to 10 megohms, where even a modern multimeter will only measure half of the voltage under normal conditions. One would not call these voltages spurious as they make the organ work.

Just as with the OP's experience, it's important to know how the test equipment functions and behaves, to make sense of the numbers appearing in the display.

 

[Lucien Nunes]

No, you are picking up induced voltages.

Most water and heating pipes are either earthed, or have a relatively low resistance and high capacitance to earth. It's unusual, although not impossible, for them to float up to significant voltage w.r.t. earth. We need to be careful not to confuse the OP, who is not experienced with making electrical measurements, with all the possibilities unless we are absolutely certain of their cause.

I have one of those and it lights up if I rub it on my knickers. I don't think I am electrified....

You would expect that. Many fabrics are triboelectric and can be charged to a high voltage by friction, which the non-contact detector correctly detects. It's handy to be able to detect such small amounts of charge, provided one understands the significance.

 

[brianmoooore]

The voltage sensed e.g. on a disconnected a.k.a. floating conductor that has significant capacitive coupling to a live one, is a real voltage. It's not unknown to read 50-100V on a long 'dead' circuit lying amongst live cables.

It's entirely possible that your (copper?) pipe is effectively a floating conductor, as above. All it takes is some plumber to fit a plastic joint or two.
Non contact voltage indicators can be very misleading, but they are still an extremely effective safety tool. Mine always goes in before my fingers, and if it lights, it means 'further investigation necessary'. Nothing more and nothing less.

 

[newfutile]

I think GN3 recommends using a voltage stick type of tester for when investigating a broken PEN conductor , as a 2 pole tester wont work without an earth reference .

 

[Lucien Nunes]

Strictly speaking, a non-contact detector such as a Voltstick also requires an earth reference, which the user supplies capacitively by holding the body of the stick. In theory, if one were in a well defined equipotential zone with lots of conductive structures connected to the MET downstream of the PEN break, it is possible that the mean capacitive reference could be above ground potential and the sensitivity of the device reduced. In the extreme case where the user is significantly capacitively coupled to a high potential, the device could light up when probing earthed metal. I had this occur and correctly identified the cause, which was a drinks chiller cabinet with live metalwork standing next to me, that had not itself been under investigation until that time as no-one had yet got a shock from it.

All of which adds to my point that these devices can do things that a 2-pole tester cannot do, but one must be very aware of the complexity of their behaviour and not put down unexplained indications to them simply being unreliable.

I am however completely with the other posters who condemn the neon screwdriver. These can be significantly dangerous in use but offer no functions that are not available from a multimeter and a Voltstick. If I see a neon screwdriver I tend to throw it in the bin, except for the museum exhibit ones.

 

[brianmoooore]

. In theory, if one were in a well defined equipotential zone with lots of conductive structures connected to the MET downstream of the PEN break, it is possible that the mean capacitive reference could be above ground potential and the sensitivity of the device reduced. In the extreme case where the user is significantly capacitively coupled to a high potential, the device could light up when probing earthed metal.

As I've posted before, I have experience of this as well.
Voltstick indicated a live earth conductor to a socket, but it turned out the earth was fine, and I was 'live'. Bare concrete floor, block and beam construction, still drying out, and a damaged live in a nearby block wall.

 

[Other_Tucker]

I had a utility room that the client had wired themselves, they were complaining of static shocks off of everything. My voltage pen went off everywhere in that room, fridge was live, washing machine and dryer were live, all the pipes were live, even walking through the door holding the pen up like a magic wand it went off.

Found 2 double sockets with no cpc fed from a god knows where boxed in join box, just building up potential in there like an enchanted kingdom