2 Pole Tester Usage

[JohnW2]

With a modern digital meter it does not even matter with D.C. If you do it the other way round it just indicates -ve volts.

That's true (of virtually all digital meters).

However, unless one sticks to a consistent convention as regards 'which probe one puts where', one then has to look to see 'how one has chosen to do it today' in order to interpret the negative sign (or its absence) in the display.

 

[plugwash]

A good habbit to get into when using test equipment on mains is that the probe on the safer terminal should be placed first and removed last.

So the probing procedure would go along the lines of.

Place black probe on the safer terminal (E is safest, L is most dangerous, N is in between).
Place red probe with display on the more dangerous terminal.
Read display
Remove red probe from the more dangerous terminal.
Remove black probe from the less dangerous terminal.

 

[Harry Bloomfield]

Yes, the problem is there is no perfect way, but the simple neon screwdriver and the two wire tested can fail to show when there is power, so I use both, test with two wire tester but also use neon screwdriver.

You are ignoring the much maligned volt-stick, which relies upon the field around a live conductor and needs neither your body, nor an earth, nor neutral.

Any test equipment used needs to be tested and proven to functional before and after the actual test in earnest is carried out. That includes neon testers, volt-sticks and two pole testers. If there is the slightest doubt about the result, you check again and maybe using an alternative method/test equipment.

Me, I tend to often work on live equipment - but I am very well used to the process, easier to fault find working equipment and sometimes impossible to diagnose it dead. It is in some ways safer to treat things as live, than be caught out by something supposedly dead which turns out not to be.

 

[Harry Bloomfield]

That's true (of virtually all digital meters).

However, unless one sticks to a consistent convention as regards 'which probe one puts where', one then has to look to see 'how one has chosen to do it today' in order to interpret the negative sign (or its absence) in the display.

Eh? There is no negative in ac mains supplies or negative sign on an ac meter range?

 

[Harry Bloomfield]

Eh? There is no negative in ac mains supplies or negative sign on an ac meter range?

[EDIT] Ignore, I hadn't realised you were replying to Winston whom I blocked long ago.

 

[Harry Bloomfield]

aha...I think that's what my Fluke T130 does. If I see -ve volts with DC, I will use that as a prompt to reverse the probes.

Still no need, they work equally well the right way, or the wrong way - you just need to be aware of that minus sign.

The red and black only become important to get right, when working with electronics - diodes and transistors etc.

To add a bit of complication - You can get DC supplies which can be positive of 0v and negative, sometimes both on the same piece of equipment. Typically desktop computers will have both and several different DC voltages available, in such circumstance it does become important to connect the black, to the 0v terminal to avoid confusion.

 

[bernardgreen]

much maligned volt-stick, which relies upon the field around a live conductor and needs neither your body, nor an earth, nor neutral.

If it is detecting a voltage "field" then it does need you body as a reference potential. If the person using the volt_stick is standing close to a Live cable then the volt-stick's reference voltage. ( the potential on the person's body ) may be close to Live voltage. Hence the volt-stick will give a false reading of no voltage when testing a conductor that is Live and may indicate Live when touching an Earthed item

If it is detecting a magnetic field from a conductor then there has to be current flowing in that conductor to create that magnetic field. The conductor could be at Live voltage but without current flowing, the volt-stick will not give a Live indication.

 

[Harry Bloomfield]

If it is detecting a voltage "field" then it does need you body as a reference potential. If the person using the volt_stick is standing close to a Live cable then the volt-stick's reference voltage. ( the potential on the person's body ) may be close to Live voltage. Hence the volt-stick will give a false reading of no voltage when testing a conductor that is Live and may indicate Live when touching an Earthed item

If it is detecting a magnetic field from a conductor then there has to be current flowing in that conductor to create that magnetic field. The conductor could be at Live voltage but without current flowing, the volt-stick will not give a Live indication.

Bernard - try it yourself. Put a volt-stick supported near a live cable with no current flowing through it, preferably one which includes a tone, walk away and see if the tone continues. It works with my Flukes..

They use capacitive coupling from live cable to the volt stick. I would guess the other pole is the air surrounding the stick.

 

[bernardgreen]

Bernard - try it yourself. Put a volt-stick supported near a live cable with no current flowing through it, preferably one which includes a tone, walk away and see if the tone continues. It works with my Flukes..

I do not have any volt-sticks to experiment with so I cannot comment on your experience.

I would guess the other pole is the air surrounding the stick

When the volt-stick is supported and not being held the air being non conductive can only be acting as a dielectric between the volt-stick and whatever object is providing the reference potential for the volt-stick

 

[Harry Bloomfield]

I do not have any volt-sticks to experiment with so I cannot comment on your experience.

OK

When the volt-stick is supported and not being held the air being non conductive can only be acting as a dielectric between the volt-stick and whatever object is providing the reference potential for the volt-stick

I'm not clear on the actual 'mechanism', all I can be sure of is that the process works quite reliably. I used to often use it across large distances, when trying to find circuit breakers to isolate circuits.

 

[EFLImpudence]

The same was said about this type of detector a while ago - that it had to be held.

 

[JohnW2]

Eh? There is no negative in ac mains supplies or negative sign on an ac meter range?

[EDIT] Ignore, I hadn't realised you were replying to Winston whom I blocked long ago.

Quite so.

Had you been 'paying attention', you would have realised the context of my comment since, even if you are 'ignoring' winston, I quoted the relevant part of his message (which was entirely about DC) in my reply to him to which you replied (and you clearly aren't 'ignoring' me!!)

Kind Regards, John

 

[Harry Bloomfield]

Quite so.

Had you been 'paying attention', you would have realised the context of my comment since, even if you are 'ignoring' winston, I quoted the relevant part of his message (which was entirely about DC) in my reply to him to which you replied (and you clearly aren't 'ignoring' me!!)

Kind Regards, John

Ignore, removes both the actual posters comment and anything you quote that you include in your reply. So all I see is the content of your reply.

 

[JohnW2]

The same was said about this type of detector a while ago - that it had to be held.....

'Holding it' (or anything like it) merely (usually) increases the amount of capacitive coupling to earth, thereby increasing the chance that it will light up/whatever when the other end is in touch with something 'live' (at a high potential relative to earth).

However, even without it being 'held', the amount of capacitive coupling to earth from the device itself may (or may not) be enough for it to 'work'.

Kind Regards, John

 

[JohnW2]

Ignore, removes both the actual posters comment and anything you quote that you include in your reply. So all I see is the content of your reply.

Oh, sorry, I didn't realise that (which is more 'clever' than I had expected)- I must say that I've never used the function', since, no matter how annoying the person, it would frustrate me not to know what others were talking about!!

Mind you, as you have just illustrated, use of that function can also result in misunderstandings !!

Kind Regards, John