what do you think of this DNO situation

[studentspark]

Called the DNO as I was getting a Ze reading of 3 ohms on a TNS system.

They changed the cutout as it was a very old cast iron head and reconnected the earth, a new silver braided cable off the supply cable to the MET. keeping it TNS

The owner said they did not test after finishing the work. DNO saying they don't test!.
I went back today and the Ze reading was still 3 ohms. So there is an issue with the external earth.
I find it hard to believe that the DNO would work like this.
I understand the DNO do not have to supply an earth, but if one is there they have to maintain it. A 3 ohm earth is not really maintained is it.

Any thoughts

 

[kai]

If this matter came to court, I'd hope that the DNO will lose the case, down to gross negligence and duty of care etc - ESQCR 2002 etc.

 

[westie101]

Get them back there to sort it out , as you say they have a duty to maintain an existing earth (though not on the same day).

 

[studentspark]

Difficult question I can imagine but, what are the likely causes of this high reading, and what can the DNO do.
If it affects one house is it likely that it will affect others in the road.
I am concerned that they say it has to be converted to a TT, which will mean expense for the house holder (new RCD board)

 

[JohnW2]

Difficult question I can imagine but, what are the likely causes of this high reading, and what can the DNO do.
If it affects one house is it likely that it will affect others in the road.
I am concerned that they say it has to be converted to a TT, which will mean expense for the house holder (new RCD board)

Common suggests that 'converting to TT' (i.e. not supplying an earth) would not be compatible with their duty to maintain an earth that they were already supplying, would it?

If the supply is actually PMEd, I imagine that conversion to TN-C-S might be another option. (I would assume that the most likely cause is damage/decay of the supply sheath).

Kind Regards, John.

 

[flameport]

I am concerned that they say it has to be converted to a TT, which will mean expense for the house holder (new RCD board)

In this area (Bournemouth/Poole), the usual fix is for the DNO to install a 100mA RCD between the meter and whatever fusebox/CU the customer has.
The cable sheath then becomes the earth rod.

As one of the DNO persons fitting it said - the alternative is to dig up most of the street, which simply won't be happening.

 

[JohnW2]

In this area (Bournemouth/Poole), the usual fix is for the DNO to install a 100mA RCD between the meter and whatever fusebox/CU the customer has. The cable sheath then becomes the earth rod.

If the cable sheath is (assumed to be) already failing somewhere, how confident can they be that it is going to remain good enough even as a TT earth?

Kind Regards, John.

 

[Guitarguy]

The dno are only obliged to supply a live and neutral, if the earth is there and tests good then we put an earth clip on the lead and a block for the customer to use, if is tests bad then we shrink heat shrink down on the sheath so it can't be used as its no good anyway. They should of tested it it's the last test of supply point testing on single phase supplies. There's not a lot of point digging up the road as it could be bad all the way to the s/s

 

[JohnW2]

The dno are only obliged to supply a live and neutral, if the earth is there and tests good then we put an earth clip on the lead and a block for the customer to use,...

Can someone perhaps clarify? Whilst it is generally agreed that a DNO is under no obligation to provide an earth, we keep being told that, if they do supply an earth, then they are then under an obligation to 'maintain' that earth (which I take to mean continue to provide a satisfactory earth connection). Is that true or not?

Kind Regards, John.

 

[westie101]

All that I can find mentioned in ESQCR is this: -

Unless he can reasonably conclude that it is inappropriate for reasons of safety, a distributor shall, when providing a new connection at low voltage, make available his supply neutral conductor or, if appropriate, the protective conductor of his network for connection to the protective conductor of the consumer’s installation.

Which has been interpreted to the meaning that DNO's only have to supply an earth for new installations.

I suspect anything further may be covered by industry Codes of Practice of individual DNOs proceedures

 

[JohnW2]

All that I can find mentioned in ESQCR is this: -

Unless he can reasonably conclude that it is inappropriate for reasons of safety, a distributor shall, when providing a new connection at low voltage, make available his supply neutral conductor or, if appropriate, the protective conductor of his network for connection to the protective conductor of the consumer’s installation.

Which has been interpreted to the meaning that DNO's only have to supply an earth for new installations.

Thanks. That seems to be a surprising 'general' interpretation, since I would have thought that, in the case of a new installation, it would rarely be possible for a DNO to 'reasonably conclude' that it would be unsafe to provide an earth.

In any event, that is obviously a bit different from the often-asserted belief that, once a DNO has supplied an earth, that they are then obliged to 'maintain' it. I wonder where (if anywhere other than mythology) that belief comes from - and, indeed, whether the DNOs themselves believe that there is any such obligation?

Kind Regards, John.

 

[17thman]

westie. I dont now how long that reg has been in situ or whether it has been in existance in another form in previous documents, but all supplies were once new. If so and that reg has been around in some form for a long period then as Johnw2 says, there is a duty to maintain the earth provided.

 

[westie101]

All I can really speak for is the DNO I work for, we do operate on the "if there is one we maintain it" principle

 

[JohnW2]

westie. I dont now how long that reg has been in situ or whether it has been in existance in another form in previous documents, but all supplies were once new. If so and that reg has been around in some form for a long period then as Johnw2 says, there is a duty to maintain the earth provided.

I guess that depends upon how inclined DNOs (and their lawyers) are prepared to adopt a 'weasel' approach. As you say, that regulation will have applied to any supply which was installed (as new) whilst the regulation was in force - but I suppsoe they could try to argue that it only applies to providing at earth at the time the new supply was provided, and says nothing about any obligation to 'maintain' that earth!

I presume that the great majority of supplies in the UK were initially provided (as new) before the ESQCR even existed, so will not have been subject to what westie quoted. However, as you say, it's possible that there were similar regulations, or at least guidelines or CoPs, in force prior to that.

Kind Regards, John.

 

[westie101]

Going back to the OP, we would either disconnect the supply and deal with it as an emergency to only restore supply with the recommended Ze of reduce the main fuse size and fit a temporary RCD until we could correct the situation.