2 Pole Tester Usage

[Jupiter01]

Can I please check what scenario would mean that my 2 pole tester doesn’t detect power across Live and Earth but does detect it across Live and Neutral?

Similarly, what would cause it to detect power against Live and Earth but not Live and Neutral?

I am thinking of a RFC situation and not lighting as lighting could have the added confusion of the Switched Live.

Currently, I test across L&E and also L&N to ensure it’s safe but unsure on why I need to do this.

Thanks in advance.

 

[AndyPRK]

if there is no earth connection, you wouldn't complete the circuit to register a voltage.
Same if the neutral was not connected

L & N also registers if reverse polarity

 

[bernardgreen]

that my 2 pole tester doesn’t detect power across Live and Earth

The "Earth" you are using is not connected to Earth. Possible due to the CPC ( earth wire ) not being connected to the MET ( Main Earth Terminal )

There are times when a genuine proven Earth is needed either as a long lead from the MET or a lead to a metal spike in the ground outside the house.

If you get to a situation where the voltage Live to Earth is low but Live to Neutral is normal voltage then you must suspect that the Earth wire is possibly Live and hence any "Earthed" metal work potentially dangerous. Touching an "Earthed" item with one hand and with the other hand touching something that is true Ground ( incoming metal pipe for example ) would give a serious electrical shock.

 

[ericmark]

As @bernardgreen says, we have a number of systems T stands for terrestrial or earth so TN the earth is bonded to Neutral, this is expanded with TN-S where earth run Separate to Neutral and TN-C where Earth and Neutral are combined (not permitted in domestic) and TN-C-S where it is combined for part of the run then separated again. Then we have TT where the Neutral is grounded at the transformer and we get the earth from the ground at the premises, this limits current flow so we need RCD protection in the main. There is also IT where we are isolated from earth, an example is output from a shaver socket.

There is a difference between earthing and bonding, with earthing we do connect to mother earth, but with bonding we just ensure all at same voltage what ever the voltage is, so finding a reference point can be a problem, I have only once worked on a large IT system, it was a Robin tunnel boring machine, and we had 220 volt phase to phase and no earth, invariable one phase would connect to earth, so any low current tester would give varying results, every one had a neon screwdriver and we tested any metal before touching it, it was rather dangerous.

But other than shaver sockets IT is rare, so in the main we can measure the voltage between a large body which will tend to be earthed and a wire, so a tester like this

will often show a voltage with one terminal held in ones hand, but don't try it with one of these

and you will get a nasty shock. I would prefer to use something designed for using the body as an earth, i.e. neon screwdriver as we really don't know if there is some thing in a two wire detector which could fail and give lethal shock. But the neon screwdriver is a two wire tester, unless you touch the top it will not show voltage this is why people say they are dangerous as we can't rely on the second connection. However used correctly they will show if what your about to touch as a significant different voltage to your body, and are very good at detecting borrowed neutrals.

Commercially we need to prove dead, and we should also do that in the home, but although I have found an isolator bridged across, in the main turn off the isolator

and there is no power, the MCB

does not isolate it only switched the line.

 

[333rocky333]

Currently, I test across L&E and also L&N to ensure it’s safe but unsure on why I need to do this.

Thanks in advance.

You should also test N to E as its not unheard of to find voltage between them too.

 

[oldbutnotdead]

Your 2 pole tester requires 1 pole to be at a known potential (0v), all your measurements will be relative to that potential.
So your testing has to start by proving earth (0v) where the supply connects to the cu/distribution and working from there (with the long earth wanderlead if needed to prove earth at the outlet).
Voltage readings from live to floating N or E can be very odd...

 

[winston1]

T stands for terrestrial or earth

T stands for terra, from the French for earth, not terrestrial.

 

[JohnD]

Latin.

cf "terra firma" "pacem in terris" "fiat voluntas tua sicut in caelo et in terra"

And "terrestrial" comes from the same root. "Of the earth"

As does "Terracotta." "Burned earth."

And "Territorial" "Territory" "Mediterranean"

 

[Jupiter01]

if there is no earth connection, you wouldn't complete the circuit to register a voltage.

Does this mean that if my earth had a continuity break a few sockets on from where I was testing and I apply my probe on Live and Earth, I would get no reading? The live could still be hot in this situation right?

 

[AndyPRK]

Correct.

 

[ericmark]

Does this mean that if my earth had a continuity break a few sockets on from where I was testing and I apply my probe on Live and Earth, I would get no reading? The live could still be hot in this situation right?

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.

 

[Jupiter01]

Wow! I hadn't appreciated that. I suppose it's probably not uncommon to have a broken earth circuit in an RFC (I have had a loose earth in one of my sockets in the past) and in that situation, if I place my probes on Live and Earth it will not report voltage - even though the Live is hot.

Do we then do the Live to Neutral test to mitigate the above risk and I suppose it's unlikely that Earth and Neutral continuity is broken. Is that the theory?

 

[EFLImpudence]

You could test between N and E on low ohms range.

There should be continuity of an ohm or so.

 

[Jupiter01]

I only have a 2 pole tester (has a voltage display). I've always assumed that when I place the probe on L and N/E, it will confirm whether I have power or not. Albeit after I have used the proving unit.
Unless I have misunderstood, the above will only be correct if there is continuity across N/E. If continuity is broken across both of these, the 2 pole tester will not detect power on Live (even if it is hot!).

Should I may be use by fluke voltage stick too?

Alternatively, should the first test with the 2 pole tester be of continuity and verify that there is indeed continuity across Neutral and Earth? And it's only once this has been successfully verified, that I should proceed with the power test across L and E/N?

Appreciate your help and guidance with this.

 

[EFLImpudence]

Touch the probes together.

Does it beep and/or show a different reading than Voltage?