Earth loop reading at 20.8 ohms!

[masona]

Hiya!

The electrician was doing some work at my bungalow, done a test on the earth loop(?) The reading was 20.8 ohms and should be 0.7 ohms, got UK Power Network in as it was urgent.

About 30 yrs ago I had the electric meter moved to external and they thought at the time there might be a poor connection or breaking away over the years. Enclosed photo, what have they done to get the reading back to 0.7 ohms?

 

[JohnW2]

Enclosed photo, what have they done to get the reading back to 0.7 ohms?

Repaired a fault in the underground cable, by the looks of it.

Kind Regards, John

 

[Iggifer]

Hard to say from just that photo, but as you had TN-S previously (a clamp around a lead sheathed cable before it enters the service head) the lead could have cracked/deteriorated in the street.

Likely now you are on PME (TN-C-S) meaning the neutral is also your earth (as they're both 0v). Or, they've re-earthed the lead sheath from where the break was.

 

[JohnW2]

Hard to say from just that photo, but as you had TN-S previously (a clamp around a lead sheathed cable before it enters the service head) the lead could have cracked/deteriorated in the street. ... Likely now you are on PME (TN-C-S) meaning the neutral is also your earth (as they're both 0v). Or, they've re-earthed the lead sheath from where the break was.

Is it not likely that they have 'repaired' a broken sheath? If they had merely converted the OP's installation to TN-C-S because of deterioration of the sheath that had been providing a TN-S earth (which is what I would have expected them to do), they surely would not have needed to do any digging, would they? Maybe there was no earthing of the neutral other than at the substation (and there was some problem in providing it), so that PME was not possible?

Kind Regards, John

 

[Iggifer]

I might be wrong, but I don't think there's any 'repairing a broken sheath' to be done. They may have put two clamps over each end of the sheath and simply resin filled the submarine over it, but I think once the sheath is gone, that's it.

Yea it might still be TN-S and hence the reason for the digging.

We don't really know what the damage to the cable was, and on a second look at the photo, there may well have already been a submarine there to begin with, they appear to be two different cables

 

[JohnW2]

I might be wrong, but I don't think there's any 'repairing a broken sheath' to be done. They may have put two clamps over each end of the sheath and simply resin filled the submarine over it, but I think once the sheath is gone, that's it.

That's what I would have thought - which is why I was struggling to think of a possible reason why they hadn't just converted the OP to TN-C-S, without the need for any digging.

I suppose it's conceivable the the high loop impedance was due to a problem with the L conductor (which, after all, is part of the 'loop' being measured), but that seems a bit unlikley.

Kind Regards, John

 

[crystal ball]

I had a similar problem, I swapped a light fitting in mates kitchen, did a loop test -25ohms, (TN-S) checked the mains and noticed the lead sheathed cable was not secured and every time the front door opened and shut the cable moved about 150mm, ENW came out and dug up the path and replaced the last few metres with split concentric