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Can Zs at DB ever be less than the Zs of the feeding circuit?

Former Community Member over 4 years ago

I am reviewing an EICR recently issued for a building with several Distribution Boards feeding sub-Distribution Boards.

I have noted that in some instances, the figure recorded for 'Zs at this board' is significantly less than the Maximum Measured Zs for the circuit recorded on the feeding DB.

e.g. DB FF4 is recorded as being fed from DB FF1. The feeding circuit to DB FF4 is recorded as having a Maximum measured Zs of 0.4 Ohm, but the 'Zs at this board' for FF4 is recorded as 0.05 Ohm - which is less than the 'Zs at this board' recorded for FF1 (0.08 Ohm) - and which, is in fact, in turn itself less than the 'Maximum measured Zs' for the circuit feeding it. Can this be true or are there errors in the report? I thought that cascaded Zs can only get larger due to the added impedance of the feeding circuits? This is not my primary area of expertise, but I am concerned that the EICR is being used to justify the upgrade of several circuits which have passed previous inspections with no problem (hope the resolution of the extracts from the EICR below are sufficient resolution to read)...

Many thanks if anyone is able to confirm my concerns or otherwise put me straight...

0 mapj1 over 4 years ago

Do not worry UKPN, the chances of being served with an N20 due to comments made on here are very slim - perhaps more likely if we were witnesses of fact - that is to say we had accompanied the chap on his apparently ill fated inspection visit. As it is we are commenting only on information presented. A written deposition in a civil case at most.

But I agree - in general in a case like this the redaction needs to be good, as we need to discuss matters 'in principle'. If a case like this arose this is the opinion.
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0 Alan Capon over 4 years ago

Sparkingchip:

. . . If that calibration certificate dated two days after the testing says it’s accurate and did not need any adjustments it is more valid proof of the accuracy of the tester used than the previous calibration certificate. . .

We only got the front page (certificate), not the results pages that back it up. These would tell how accurate it was when received and what was done.

Regards,

Alan.
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0 Chris Pearson over 4 years ago

Peter S3:

Which raises the question: what would folks advise should be my next step? The trustees have no confidence to invite the original contractor to repeat/correct the report, and it does not appear that he is NICEIC approved (I was not involved in his initial selection). I am considering to ask whether he wishes to retract his report or allow us to submit it for independent review - with potential resulting claim through legal channels.

I can understand why the Trustees have no confidence in the report.

I think that the first step should be to make the contractor aware of their dissatisfaction. If he is not a member of any professional body, then clearly there will be no possibility of redress there. Being rather pessimistic, it may be necessary to get a new report and the Trustees can consider whether to seek redress for breach of contract.

Good luck!
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0 Sparkingchip over 4 years ago

Alan Capon:
Sparkingchip:

. . . If that calibration certificate dated two days after the testing says it’s accurate and did not need any adjustments it is more valid proof of the accuracy of the tester used than the previous calibration certificate. . .

We only got the front page (certificate), not the results pages that back it up. These would tell how accurate it was when received and what was done.

Regards,

Alan.

Agreed, it depends on what the whole calibration certificate says, not just the front page.

Andy Betteridge.
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0 Sparkingchip over 4 years ago

For an installation that appears to have been installed around the 1960's the EICR from five years ago was remarkably free of observations, whilst the latest EICR has some unconvincing observations.

It appears that the contractor needs to reattend site to check some details and tidy up the report, if the contractor has not been paid the trustees have some leverage to help resolve the situation. Personally I carry a camera and take a considerable number of photographs whilst inspecting and testing, all dated stamped, should someone raise a question at least I can start emailing photos to back up my comments and conclusions. I actually have a camera I just use for EICRs and a routine that starts with taking a photo of the job sheet, followed by the exterior of the building, working through the I&T and finishing up with my notes. So if I said cables were leaching plasticiser I would have photos to prove it.

If the contractor won't resolve the issues then you have little choice other than to commission another report, how you now choose another contractor is open to discussion, but I would not be surprised if the third report has a few observations on it unlike the one from five years ago, apart from anything else there have been changes in the Wiring Regulations over the last fifty years and the new EICR will be comparing it to the latest regulations.

Regards legal action, what for? If the bill has not been paid and the trustees refuse to pay it, it would be up to the contractor to take the trustees to court for non-payment. If the bill has been paid it's up to the trustees to try and claim their costs back for having yet another EICR completed, if someone got in touch with me asking me to do an EICR and then potentially be an expert witness in court to prove the other EICR was inadequate I would decline the job, I have been an expert witness in court and for something like this it wouldn't be worth the hassle.

The trustees are probably going to have to get another EICR produced by another contractor, who should be provided with a copy of the EICR from five years ago to work off, then when they have the new report decide what actions to take, unless the last contractor steps up and resolves the issues.

Andy B.
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0 Sparkingchip over 4 years ago

On the EICR it should say that records are available and are held by the trustees, these records should have been made available to the inspector.
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0 Former Community Member over 4 years ago

Sparkingchip:

On the EICR it should say that records are available and are held by the trustees, these records should have been made available to the inspector.

He has ticked to say he has seen evidence of installation documentation;
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0 Sparkingchip over 4 years ago

The only information available to me for the one I posted was an EICR sticker with a date on it on the replacement consumer unit that was installed four years ago, without actually seeing the documentation it's a no from me, despite having recorded the date of the last inspection.

There seems to be far too many loose ends with the EICR that was done at the church leaving too many questions, such as did the inspector actually see the previous EICR or not? In addition to the previous EICR the paperwork for the additions or alterations made since then three years ago should also have been made available to the inspector.

There should be a file of relevant paperwork, ideally kept on the premises and available to all electricians and others who may have reason to see it.

Andy B.
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0 Former Community Member over 4 years ago

Peter S3:

"I assume it’s the rubbish software used for this forum, both reports have disappeared.

No, sorry, I removed the attachments as I realised that the redacting was not 100%. Since it is looking like the trustees will need to be seeking resolution on this, I need to be careful.

I may re-post once I have double-checked the redaction.

Which raises the question: what would folks advise should be my next step? The trustees have no confidence to invite the original contractor to repeat/correct the report, and it does not appear that he is NICEIC approved (I was not involved in his initial selection). I am considering to ask whether he wishes to retract his report or allow us to submit it for independent review - with potential resulting claim through legal channels.

Hi Peter, fair point thanks for letting us know. It is not an easy position to be in. Do you know if there have been any alterations between the previous and current EICR?

Would some anonymous pics of similar DBs and the C2 areas be available?
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0 Former Community Member over 4 years ago

I've made the 2015 and 2020 reports available for viewing again - I think you will find them back under their original posts.

Also, please see below latest attempt to justify their quote to install a new cable feed to DB GF2, after I pointed out that we had proven that DB GF2 was fed by a 3-phase 100A MCCB and not a 1-phase 32A MCCB;

I will be interested to see if you come to the same conclusion on their cable calcs as I did;

"Yes, sorry you are correct on the routing of the feed to GF3. Unfortunately there was some confusion at our end regarding “feed to Boiler Room” and assuming this was the feed to GF2.

However although this means that there is not a MCB Discrimination issue, there is still the problem that way GF3 is fed, results in excessive voltage drops on full load and the Disconnection tomes of the RCBO FAILS test.

Attached is our cable sizing report based on feeding GF3 the way it is currently fed. As you can see it FAILS on all three calculated headings.

Based on this our recommendation to run a new feed direct from MF1 to GF3 stands as this is the only way the required disconnection times and impedances can be achieved. It will also overcome the potential full load Voltage Drop issue.

Please digest the attached report."

(pages 2 details a different circuit not part of this issue).

Page 3 (below) details their proposed new circuit to GF2;
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Can Zs at DB ever be less than the Zs of the feeding circuit?

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