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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details. |
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21st Jul 2022, 8:49 pm | #1 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,609
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EICR unearthed an unearthed TT
We were doing an EICR on a TT house installation the other day and measured a Ze of 408Ω .... so we took the lid off the earth rod terminal box, only to find it full of - earth. The 10mm PE was fitted with a suitable crimped terminal, but it wasn't connected to the the clamp on top of the earth rod. I can only think that someone thought it was amusing to "Earth" the system is this way.
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Richard Index: recursive loop: see recursive loop |
21st Jul 2022, 11:15 pm | #2 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,723
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Re: EICR unearthed an unearthed TT
A bit like connecting a radio set earth terminal to a rod in a plant-pot. Such plant-pot earths were actually sold to the gullible.
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-- Graham. G3ZVT |
22nd Jul 2022, 1:59 am | #3 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,554
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Re: EICR unearthed an unearthed TT
If it was for an audio reason the earth wire should have been routed to a coal bunker surely
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22nd Jul 2022, 7:15 am | #4 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,609
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Re: EICR unearthed an unearthed TT
The house is in South Wales - no need to look far for coal, a working earth rod would do it by default. Maybe the house could be sold, when the earth fault is corrected, as an audiophile listening chamber?
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Richard Index: recursive loop: see recursive loop |
22nd Jul 2022, 9:05 am | #5 | |
Octode
Join Date: Jul 2004
Location: Dundee, UK.
Posts: 1,813
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Re: EICR unearthed an unearthed TT
Quote:
I wonder what they would make of C & G 2382, 2392 and 2393, just the names I mean, let alone what they stand for. PMM |
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23rd Jul 2022, 10:17 pm | #6 |
Nonode
Join Date: Aug 2010
Location: Resolven, Wales; and Bristol, England
Posts: 2,609
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Re: EICR unearthed an unearthed TT
Unfortunately I think you might be correct. I have C&G 2392 and I was an accredited tutor on C&G 2399 where my experience did not fill me with confidence.
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Richard Index: recursive loop: see recursive loop |
23rd Jul 2022, 11:07 pm | #7 |
Pentode
Join Date: Mar 2022
Location: Retford, Nottinghamshire, UK.
Posts: 195
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Re: EICR unearthed an unearthed TT
Reminds me of something TT related I saw at a neighbour's. We are all on TT here, and they had just had a solar panel installation. He was showing me the installer's handywork in the cubby hole built around the meter and fusebox (still on Wylex rewireables), when I noticed something odd.
The cubby had been built over the main earth block, making it inaccessible - so the installer had put the earth for the solar inverter and panels into the neutral...
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Paul |
24th Jul 2022, 8:53 am | #8 |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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Re: EICR unearthed an unearthed TT
If the supply is TN-C-S that's naughty but not very dangerous. If it's traditional TN-C with no nearby CNE, or TT, it gets more dodgy.
Working mainly on large non-domestic installations we don't tend to see bodges on the service equipment like DIY TN-C-S, BS951 clamps on PILC, etc. We did find a 315A intake at a college earthed by a loose M6 roofing bolt. |
24th Jul 2022, 10:04 pm | #9 |
Pentode
Join Date: Mar 2022
Location: Retford, Nottinghamshire, UK.
Posts: 195
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Re: EICR unearthed an unearthed TT
Certainly gets interesting if a TT neutral to the building becomes accidentally disconnected - certainly not beyond the realms of fantasy when the two conductors are fed from the pole by singles.
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Paul |
24th Jul 2022, 10:31 pm | #10 | ||
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Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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Re: EICR unearthed an unearthed TT
Quote:
Quote:
My comment about the retrospective TN-C-S for the solar inverter being potentially dangerous (see what I did there?) ws referring to two different 'versions' of earth, one from the rod and one from the neutral, existing side by side in what is supposed to be an equipotential zone. The TT earth becomes an unbonded extraneous conductor relative to the TN earth. Last edited by Lucien Nunes; 24th Jul 2022 at 10:40 pm. |
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24th Jul 2022, 11:11 pm | #11 | ||
Pentode
Join Date: Mar 2022
Location: Retford, Nottinghamshire, UK.
Posts: 195
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Re: EICR unearthed an unearthed TT
Quote:
If the neutral was disconnected from the building, the neutral inside the building (and indeed the solar panel earth) would rise to live, back fed through any connected appliances. Under normal circumstances, no neutral would not trip the incomer RCD... but with the neutral connected to the solar panel earth?
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Paul |
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24th Jul 2022, 11:20 pm | #12 | |
Rest in Peace
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
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Re: EICR unearthed an unearthed TT
Quote:
Since the RCD is in the neutral only, downstream of the neutral-earth link, it does nothing to protect against open CNE. This is a big deal with equipment used outside the equipotential zone and new monitoring devices are on the market to deal with the scenario by disconnecting all three conductors in the event of a CNE loss. |
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