What is this megger code?

[HappyHippyDad]

My megger 1741 has come up with the code seen in the video clip.

I was doing a Ze. I disconnected the main earth from the earth bar in the CU when testing.

I believe that it means it would not let me carry out the test as the 'touch voltage' would be too great, but I don't know what the Ut bit means or even if I have interpreted the result correctly?

When I connect the main earth back into the earth bar (therefore including bonding) of the CU it then lets me test for a Ze (0.19ohms).

This was the top floor flat. I had no access to the meter or cut out.

261V,
Ut >50V

50V

 

[Ian1981]

My megger 1741 has come up with the code seen in the video clip.

I was doing a Ze. I disconnected the main earth from the earth bar in the CU when testing.

I believe that it means it would not let me carry out the test as the 'touch voltage' would be too great, but I don't know what the Ut bit means or even if I have interpreted the result correctly?

When I connect the main earth back into the earth bar (therefore including bonding) of the CU it then lets me test for a Ze (0.19ohms).

This was the top floor flat. I had no access to the meter or cut out.

261V,
Ut >50V


View attachment 60301

The touch voltage to earth has exceeded 50v meaning there’s no earth connection or lack of earth continuity to what you are testing.
Modern meters will not allow the test to be performed if this is detected for safety reasons as injecting a test current will raise the unearthed conductor and whatever it’s connected to , to potentially mains voltage for the duration of the test.

 

[HappyHippyDad]

The touch voltage to earth has exceeded 50v meaning there’s no earth connection or lack of earth continuity to what you are testing.
Modern meters will not allow the test to be performed if this is detected for safety reasons as injecting a test current will raise the unearthed conductor and whatever it’s connected to , to potentially mains voltage for the duration of the test.

So are you saying that means the main earth does not have continuity back to the cut out or supply sheath depending on the earthing arrangement?

 

[pc1966]

Sounds like it. Can you do a continuity check between the bonded MET and the supply earth? If open you have your answer!

 

[Ian1981]

So are you saying that means the main earth does not have continuity back to the cut out or supply sheath depending on the earthing arrangement?

Have you measured the voltage between line and with the earthing conductor removed from the MET inside the CU?

 

[HappyHippyDad]

Sounds like it. Can you do a continuity check between the bonded MET and the supply earth? If open you have your answer!

I did, with a T5-600. On continuity setting it made its sound, but it was a gurgling sound which I'm also not too sure what it means and can't find a decent manual.
I feel my hole being dug

Have you measured the voltage between line and with the earthing conductor removed from the MET inside the CU?

No, I didn't. I got carried away by the plethora of other problems! No excuse. I'm going to go back!

 

[pc1966]

I did, with a T5-600. On continuity setting it made its sound, but it was a gurgling sound which I'm also not too sure what it means and can't find a decent manual.

Possibly some induced voltage confusing it.

Whatever the reason, something is wrong with the supply earth!

 

[davesparks]

Something is defiantely wrong there, 261V is out of tolerance for the supply for a start which sets and alarm bell ringing in my head.
Connecting the main bonding is likely connecting this installation to the other flats via the bonded metalwork.

Are you sure you identified the incoming CPC of the submain correctly? i know this might seem like a daft/obvious question but in a flat which is undoubtedly fed via a submain it may not be so obvious.

As a side note, if you are not testing at the incoming supply position then it isn't Ze, you are measuring the Zs of the submain which is feeding this CU (I assume the meter isnt within 3m of the CU as it is a top floor flat)

What is preventing access to the cutout/meter/switch fuse?

 

[HappyHippyDad]

Something is defiantely wrong there, 261V is out of tolerance for the supply for a start which sets and alarm bell ringing in my head.
Connecting the main bonding is likely connecting this installation to the other flats via the bonded metalwork.

Are you sure you identified the incoming CPC of the submain correctly? i know this might seem like a daft/obvious question but in a flat which is undoubtedly fed via a submain it may not be so obvious.

As a side note, if you are not testing at the incoming supply position then it isn't Ze, you are measuring the Zs of the submain which is feeding this CU (I assume the meter isnt within 3m of the CU as it is a top floor flat)

What is preventing access to the cutout/meter/switch fuse?

Thanks for the correct terminology regarding Ze and Zs.
Here is a picture of the CU and Henly blocks.
I removed the far left CPC which leads down to the Henly block (although i didn't physically remove the din rail, but the bonding conductors are the 2 other 10mm's), it then connects to the 6mm of the 16mm twin and earth (which has been twisted into 2 separate parts as it enters the henly block).

 

[pc1966]

it then connects to the 6mm of the 16mm twin and earth (which has been twisted into 2 separate parts as it enters the henly block).

Odd to do that. After all, one aspect of Henley blocks is they reliably terminate conductors to at least 25mm!

Might be worth an internal inspection of that block, and obviously to see about access to the source end of the T&E feed.

Of course, as T&E without an earth shield it needs to either be RCD protected or run in such a way that it is not buried in walls less than 50mm from surface, etc.

 

[Lucien Nunes]

I don't know what the Ut bit means or even if I have interpreted the result correctly?

Ut = touch voltage. Yes, your understanding is correct.

it was a gurgling sound

Agree that this is likely due to the presence of a voltage between the two points being tested, which corroborates the loop impedance test result that there is something wrong with the submain CPC or its connection to earth. An AC voltage (that alternately adds to and subtracts from the tester's own applied voltage) can cause a circuit appear to the tester to be making and breaking continuity 50 times per second, hence its tone being modulated on and off.

 

[davesparks]

Thanks for the correct terminology regarding Ze and Zs.
Here is a picture of the CU and Henly blocks.
I removed the far left CPC which leads down to the Henly block (although i didn't physically remove the din rail, but the bonding conductors are the 2 other 10mm's), it then connects to the 6mm of the 16mm twin and earth (which has been twisted into 2 separate parts as it enters the henly block).
View attachment 60311

Well that looks lovely,

They've probably split the cpc because the sleeving they had wasn't big enough to fit over it, I've had to resort to doing the same once or twice.

I think you need to gain access to the incoming supply to get any further with this,

 

[pc1966]

Also looks like the left-most pipe might have had a bonding clamp at one time.

The ropey T&E presentation does not bode well for the other end!

 

[HappyHippyDad]

I'll update after my return visit.

 

[HappyHippyDad]

Back at the flat.
L- main earth 261V (main earth disconnected from earth bar in CU)
L - earth bar in CU (main earth still in earth bar OR disconnected) 238v
No continuity between main earth and earth bar in CU (with bonding connected in CU).
32v main earth( disconnected) - earth bar in CU (Bonding connected)

I'm investigating at present, but I can't understand why 261V if the earth isn't connected to earth? If there is a break in the main earth there wouldn't be any circuit?