Codes for this EICR?

[HappyHippyDad]

This is a follow on from my thread regarding the megger code that I did not understand What is this megger code? - https://www.electriciansforums.net/threads/what-is-this-megger-code.189699/

I conducted an EICR on a top floor flat but did not have access to the room which stored the meters and cutouts.

Previously my megger was not letting me obtain a Zs at the consumer unit and was saying 261V Ut >50v.

I have today gained access to the meter room and discovered there was no continuity between the earth in the switch fuse, and the Main Earthing Terminal for all the flats. This has been remedied with a 16mm earth. However, the meter room looks awful....

It looked like an earth went from top flat switch fuse to off peak switch fuse and then into another flats switch fuse and so on, but did not get back to the MET. Is it normal for the Main earth to meander between different flats switch fuses before a single cable goes from the last switch fuse to the MET? Should they not have a separate cable for each flat?

Also, the supply cable looks dire (see pictures), but I have not studied a new piece of this cable so am unsure what it should look like and whether the state it is in is dangerous?

Lastly, the TNS seems to have a bonding clamp rather than the usual joint I see on a TNS, this is not a proper TNS joint so would you be contacting the DNO for this?



Cheers all

 

[pc1966]

The wires to that bond clamp are green, suggesting it is pre-1977 installation for that, though the meters seem to span many decades!

I guess other flats also had no earth continuity then? Wonder if other EICR just skipped that bit?

I have no idea what is considered proper for the earth route, but to me the first choice would be a large enough MET to take separate wires from each flat's switch-fuse. If impractical, I would at least run the CPC round as a ring back to the MET so there is a redundant path in case of a bad joint, etc.

Hopefully others here can provide more useful inputs.

 

[HappyHippyDad]

The wires to that bond clamp are green, suggesting it is pre-1977 installation for that, though the meters seem to span many decades!

I guess other flats also had no earth continuity then? Wonder if other EICR just skipped that bit?

I have no idea what is considered proper for the earth route, but to me the first choice would be a large enough MET to take separate wires from each flat's switch-fuse. If impractical, I would at least run the CPC round as a ring back to the MET so there is a redundant path in case of a bad joint, etc.

Hopefully others here can provide more useful inputs.

Thanks for that PC. How about the condition of the supply cable, the outer sheathing/insulation is falling apart in places as seen in the pictures?

I do think that perhaps electricians sometimes skip taking the main earth out of the earth bar for the Ze, hence not getting a correct result and on occasion missing this type of fault.

 

[pc1966]

Thanks for that PC. How about the condition of the supply cable, the outer sheathing/insulation is falling apart in places as seen in the pictures?

I don't know enough about those cables really to comment, but I would try and forward a photo to the DNO (assuming they have a facility to receive it!) for this take on that matter. Same for the earth clamp, it is not looking that bad and could well be original, but it has a bit of a pipe-bond look to it.

 

[ipf]

The cable, I would say, is an old lead sheathed and, as a result, will be perfectly OK. The connection should really be renewed by the DNO...should be a soldered connection to the lead, although a constant pressure spring clip will suffice. (Hepworth)

edit. What type of clip is on at present?...can't tell from the photo.

 

[HappyHippyDad]

One more thing, why was I getting 261V from the line to the disconnected main earth (which wasn't connected to earth)? There was no circuit, so it was just like connecting to a random piece of metal which didn't go anywhere.

Ps.. sorry @ipf I don't know the name of the clamp.

 

[ipf]

One more thing, why was I getting 261V from the line to the disconnected main earth (which wasn't connected to earth)? There was no circuit, so it was just like connecting to a random piece of metal which didn't go anywhere.

Is that in the flat or at the supply point? If it's at the flat, it could be parallel paths. Have you tested for all details in the sub room, the actual incomer?

edit. Some of those outgoing T&E's look a bit old and ropey, by the way.

 

[davesparks]

I do think that perhaps electricians sometimes skip taking the main earth out of the earth bar for the Ze, hence not getting a correct result and on occasion missing this type of fault.

This type of fault should be found visually before testing for Ze.

Don't forget that you weren't testing Ze at the flat, you were testing the Zs of the submain, but with the CPC of the submain disconnected. Which is the incorrect procedure for testing Zs as all protective conductors must be connected before carrying out the test.

If when you carried out the Zs test with the CPC disconnected you had got an acceptable result what woukd you have done next? Would you have written it down as Ze and carried on without checking the intake position?

What you see on the outside of the supply cable is the tar soaked jute serving on the outside of the cable cracking, it is an additional protective layer over the lead sheath. It's similar to seeing the PVC sheath of MICC damaged by sunlight, it's not pretty but it doesn't affect the cable.
[automerge]1598802656[/automerge]
It's hard to tell from the picture but I think that is one of the older type of clamos designed for connecting to the lead sheath of the cable. A side view would help.

All those green protective conductors leaving the room are likely to be the original bonding to each flat, at a guess it has probably been disconnected in your flat by whoever did the shoddy board change through a lack of checking/understating on their part.

As for linking all the switch fuses tigether with a single earth, yes this was acceptable and still is. Those older switch fuses and other switchgear/DBs had an earth terminal or bolt on the outside of the enclosure for this purpose.

 

[snowhead]

That cable has a steel band under the outer covering and it's corroded.
If that location is in a cellar then it's most likely water has got into the cable outside and crept down the outer corroding the steel band as it goes.

The clamp looks to be the type the DNO would use and no-one else and also looks like it's on the lead not the steel

 

[davesparks]

That cable has a steel band under the outer covering and it's corroded.
If that location is in a cellar then it's most likely water has got into the cable outside and crept down the outer corroding the steel band as it goes.

View attachment 60490

View attachment 60491

Yes there may be steel tape or wire armour, in there. These are mechanical protection for the cable which is additional to the cable rather than being an essential part of it.
The armour, whether it is tape or wire, does not form part of the protective conductor and the cable is electrically sound without it.

Whilst it is obviously degraded and far from in ideal condition the DNO won't do anything with it as it is still serviceable.

 

[pc1966]

One more thing, why was I getting 261V from the line to the disconnected main earth (which wasn't connected to earth)?

If the open-CPC was near another phase it could well be seeing the ~415V phase-phase voltage reduced by whatever capacitor-divider effect there is.

 

[davesparks]

One more thing, why was I getting 261V from the line to the disconnected main earth (which wasn't connected to earth)? There was no circuit, so it was just like connecting to a random piece of metal which didn't go anywhere.

I am a little confused by the 261V, as the switchfuses were linked together it should have found a route to earth via the other installations.
This suggests that the CPCs of the submains are all cut off at the load end and have been replaced by the green protective conductors seen in your first picture. (I've seen this before where a 16mm T&E has its earth cut off and a seperate 10mm taped to the outside of it used instead)

If all those other CPCs were cut off and only connected to each other, not to earth at all, then that's quite a bit of capacitive coupling to give you an unusual voltage reading. This is just guesswork on my part though.

 

[HappyHippyDad]

If the open-CPC was near another phase it could well be seeing the ~415V phase-phase voltage reduced by whatever capacitor-divider effect there is.

I am a little confused by the 261V, as the switchfuses were linked together it should have found a route to earth via the other installations.
This suggests that the CPCs of the submains are all cut off at the load end and have been replaced by the green protective conductors seen in your first picture. (I've seen this before where a 16mm T&E has its earth cut off and a seperate 10mm taped to the outside of it used instead)

If all those other CPCs were cut off and only connected to each other, not to earth at all, then that's quite a bit of capacitive coupling to give you an unusual voltage reading. This is just guesswork on my part though.

So would this 261V only show up on a digital tester? If I used a drummond test lamp would it still show any voltage?

 

[pc1966]

So would this 261V only show up on a digital tester? If I used a drummond test lamp would it still show any voltage?

Pretty much so. The likes of voltage testers typically need a couple of mA to work so don't respond to most "phantom voltages" the way a multi-meter with its 10M impedance does.

 

[HappyHippyDad]

Pretty much so. The likes of voltage testers typically need a couple of mA to work so don't respond to most "phantom voltages" the way a multi-meter with its 10M impedance does.

I'm not too sure if you meant this voltage would or wouldn't show with a drummond pc1966? Sorry
I'm pretty sure you said it wouldn't show up with a drummond, if so I wish I'd popped the drummond on it just to see!

 

[pc1966]

No it would not show on the Drummond as typically the capacitive current is quite small so even if it shows it would be a a very much lower voltage.

 

[Lucien Nunes]

Lots of good information above. I agree generally:

1. The floating CPC can drift anywhere including towards another phase if it is connected to another floating installation, so 261V line-CPC is feasible. It probably won't show up on a Drummond tester. You can work out what leakage currents will register on a voltage scale using Ohm's law, multiplying the leakage current by the input resistance of the tester. E.g. 1mA on a tester with 10kΩ input resistance would show as 0.001 x 10,000 = 10V. There are some subtleties but it gives an idea. (The resistance of the tester and the capacitive reactance are in quadrature so they don't add alegbraically, but as you don't know the actual phase angle of the leakage current, part of which might be resistive, it will only be an approximation)

2. Re:

One more thing, why was I getting 261V from the line to the disconnected main earth (which wasn't connected to earth)? There was no circuit, so it was just like connecting to a random piece of metal which didn't go anywhere.

When there is AC about, it will couple capacitively to any piece of metal. The bigger the piece of metal, the higher its stray capacitance so the lower the capacitive reactance (AC resistance) so the more current can be drawn from the piece of metal by the meter. A screw lying on the bench will have such a low capacitance and therefore such as high reactance at 50Hz that you can't measure anything from it with a multimeter. But the CPC system of an entire installation, bundled with lots of live line conductors and snaking around for tens or hundreds of metres, will have a reactance low enough to source sufficient current into the meter to make it register a reasonable approximation of its true voltage. But in turn, probably not enough to make the Drummond register more than an unreadable tiny fraction of the true voltage.

Remember, 'ghost voltage' is just a concept popular amongst superstitious electricians who can't be bothered to interpret or understand every measurement as a voltage divider consisting of the circuit under test and the meter input. In precision and RF electronics, often one has to see all measurements like that, a combined system of the device under test and the instrument, and correct every measurement to allow for the influence of the test on the circuit. The floating CPC truly is at 261V wrt the line due to the aggregate leakage; the multimeter displays this accurately, the Drummond deliberately influences it by its low input resistance and doesn't register the voltage 'accurately'. However, it usefully tells you without need of further measurements, that the source of the 261V has such as high impedance that it must be leakage and not an actual connection to an energy supply of 261V.

2. The daisy-chain connection of the SF's to the MET might be acceptable, however it ought to meet the requirements of high-integrity CPC as it would be expected to carry significant leakage.

3. The clamp on the incomer lead looks like a constant-pressure type designed for the purpose and is probably correct.

4. The tarred jute serving is peeling off the cable but the STA looks OK inside, and the lead will be fine inside that. Nothing unusual to worry about as far as I can see.

 

[HappyHippyDad]

I really appreciate all the comments above. Some have gone into great detail and were very interesting to read.

Thanks