High Ze reading fails EICR

[Maarel]

Hello there. I've been looking around here and found some conflicting information. I have a question if I may ask. I had an electrician come over to perform an EICR, and all the installations were in good nic. However, he said that the Ze measurement was 14.5 Ohms on a TNS system, so he refused to sign it off. I've arranged for the DNO to investigate, and they say that our stairwell need to be rewired due to outdated wiring, which would take them 1-2 months. The issue is that I need a valid EICR in a maximum of two weeks, and I'm wondering if there's any chance he could have signed this off as satisfactory, considering that the dwelling's electrical installation is protected by an RCD, which, if I understand correctly, would isolate the system within the required 0.4 seconds in case of an Earth fault.

 

[westward10]

This all sounds very confusing. Firstly EICRs do not fail they are either satisfactory or unsatisfactory. Secondly you don't refuse to sign it off, observations are Coded and noted in the Report and submitted to the client. Thirdly why are the DNO suggesting your stairwell needs rewiring which could take up to two months. What exactly needs rewiring, their supply or your stairwell wiring?

 

[Maarel]

This all sounds very confusing. Firstly EICRs do not fail they are either satisfactory or unsatisfactory. Secondly you don't refuse to sign it off, observations are Coded and noted in the Report and submitted to the client. Thirdly why are the DNO suggesting your stairwell needs rewiring which could take up to two months. What exactly needs rewiring, their supply or your stairwell wiring?

My apologies for being confusing. Yes, he mentioned that he couldn't sign off the EICR with high Ze readings. He explained that if someone were to see that he had issued a satisfactory EICR under those conditions then he could get in trouble, he said he would return to retest and issue a satisfactory EICR once the earth issue is resolved. He didn't assign a specific fault code; I asked him for an EICR, and he stated that he could only provide it as unsatisfactory.

I live in an 1890 tenement building. The DNO guy says that the entire block stairway needs to be rewired, the part from the street to each flat.

 

[plugsandsparks]

The earth reading is poor and it makes all the individual ccts fail the maximum allowed readings. When i have come across such instances i have aborted the testing until the earth has been corrected. It will need testing again when the earthing system has been improved anyway (ze at least).
Suggest address the DNO as i would be worried (and it sounds like it affects multiple homes) that i and others have a poor electrical installation that cannot react correctly to all possible fault types.

 

[Rockingit]

Firstly, the ‘inspector’ is way off the mark. They are required to issue a report regardless of the ultimate outcome so therefore should have just noted this issue on the report they produced. Secondly, whilst it sounds like this situation does indeed need investigating/resolving it needs to be taken in a greater context - Ze isn’t generally speaking an issue, Zs IS, however if circuits are RCD protected then this becomes a moot point. Which basically in layman’s terms means making a decision on whether or not something is likely to harm someone before it gets fixed.

 

[Maarel]

Firstly, the ‘inspector’ is way off the mark. They are required to issue a report regardless of the ultimate outcome so therefore should have just noted this issue on the report they produced. Secondly, whilst it sounds like this situation does indeed need investigating/resolving it needs to be taken in a greater context - Ze isn’t generally speaking an issue, Zs IS, however if circuits are RCD protected then this becomes a moot point. Which basically in layman’s terms means making a decision on whether or not something is likely to harm someone before it gets fixed.

Many thanks. I have a feeling that something is off with this guy. I was just wondering if he could have coded this as C3, or is it more likely to be C2 or even FI? I understand that that’s he’s decision to make but would like to hear other seasoned electricians take on this.

He conducted R1+R2 tests for all circuits and mentioned that the resistance readings were acceptable. He also tested the RCDs, and all the tests passed, as did the insulation resistance tests.

 

[westward10]

I would Code 2 it, the fact it has RCD protection is not really relevant as you cannot rely on an RCD for protection in the absence of an earth.

 

[pc1966]

Following the BPG#4 guidance this would be a C2 for "Absence of a reliable and effective means of earthing for the installation" so unsatisfactory.

If the DNO supply has a failing earth (which is pretty much what has been measured) then all of the supplied flats are at risk. It is possible that the Zs due to bonded service pipes will be much lower if they are in turn linked to properties with good earthing, etc, but that is not something you can depend upon (basically it only takes a plumber to replace a section in plastic, or use a plastic push-fit joint, and it is gone).

It is also true that RCD/RCBO protection would deal with such a high Ze for faults downstream of the devices, but any fault on the cables feeding the flats would leave the installation metalwork at a dangerously high voltage, as well as faults in any flats sharing the faulted earth connection that have MCB-only protection for any circuits.

While the DNO is proposing to replace the old failing cable here, in some cases where the DNO earth is no longer acceptable they will not do anything about it and instead you need to convert the property to a TT earth arrangement using a suitable earth rod instead of using the DNO's connection. Although the design of a TT installation is not very different to a modern all-RCD/RCBO protected installation, the Devil is in the details of lowered risk for faults pre-RCD as they simply will not clear on the typically available earth.

If you absolutely must have it solved before the DNO can act, and there is a sane route for a separate TT earth to a rod, then having an upfront delay RCD fitted and making it TT for now is an option to discuss with your electrician.

 

[loz2754]

they will not do anything about it

I thought the ESQCR required the DNO to maintain any earth that they provide.

 

[kropaske]

This is interesting scenario. Seems that DNO are very slow in response to this situation. When I had similar readings on the job they were within couple of hours not months digging outside.
But assuming there is relatively new CU with tails nicely glanded and secured and all circuits RCD protected. The path to earth exist but it's high resistance, which will be rectified by DNO. What danger is actually present to the occupiers with Ze of 14.5ohms
Are the readings within limits - NO
Will RCD provide fault protection within specific time for all circuits - YES
So where is potentially dangerous situation here? Can we not rely on RCD for fault protection in a same way we do on TT, just for the time until repair is done, then revisit and retest?

 

[Mike Johnson]

The issue is that I need a valid EICR in a maximum of two weeks, and I'm wondering if there's any chance he could have signed this off as satisfactory, considering that the dwelling's electrical installation is protected by an RCD, which, if I understand correctly, would isolate the system within the required 0.4 seconds in case of an Earth fault.

First why do you need a valid EICR in two weeks? are you letting the property?
The RCD protection will not work effectively/efficiently without a satisfactory Earth.
Looks like your only route is to install an earth rod and delay type RCD as pc1966 suggests.
Your electrician should have issued an EICR with the content noted, this at least shows willing on your part if you are letting out the apartment.

 

[pc1966]

I thought the ESQCR required the DNO to maintain any earth that they provide.

Almost. What it actually says is:

Equipment on a consumer’s premises
24.—(1) A distributor or meter operator shall ensure that each item of his equipment which is on a consumer’s premises but which is not under the control of the consumer (whether forming part of the consumer’s installation or not) is—

(a) suitable for its purpose;​

(b) installed and, so far as is reasonably practicable, maintained so as to prevent danger; and​

(c) protected by a suitable fusible cut-out or circuit breaker which is situated as close as is reasonably practicable to the supply terminals.​

​

The catch is "so far as is reasonably practicable" which I have heard leads to occasions when they simply decide it is not practical / cost-effective to replace something.

 

[westward10]

This is interesting scenario. Seems that DNO are very slow in response to this situation. When I had similar readings on the job they were within couple of hours not months digging outside.
But assuming there is relatively new CU with tails nicely glanded and secured and all circuits RCD protected. The path to earth exist but it's high resistance, which will be rectified by DNO. What danger is actually present to the occupiers with Ze of 14.5ohms
Are the readings within limits - NO
Will RCD provide fault protection within specific time for all circuits - YES
So where is potentially dangerous situation here? Can we not rely on RCD for fault protection in a same way we do on TT, just for the time until repair is done, then revisit and retest?

14.5 ohms today but what will it be in a weeks time. With TT we have a reference for the fault path but can this be compared.

 

[pc1966]

So where is potentially dangerous situation here?

In most cases the risk is low, but seeing 14.5 ohms for a TN earth means that some cable corroded or loose to the point of barely conducting. In the event of a high current fault I would expect that to blow open. After someone resets the MCB/RCBO no more earth and ADS.

Now it might be OK, it might be the cable has opened / corroded through at a far end and really is a 14.5 ohm earth rod now, so it would take the fault energy with only warm earth around it, but it is not known so not something that would make me sleep easy.

edit: beaten to it by @westward10

 

[kropaske]

@pc1966 , @westward10
I take both of you points guys but we only testing on the day and we can't really assume how long this fault was preset, and whether it will get worst in a day or year. We also know that repair is arranged. Whether satisfactory or not, would you leave this installation live and walk away? Why not for example make it satisfactory and schedule weekly visits to verify that connection it's still there untill repair is complete. Would that not be better then just give unsatisfactory and walk away.