Domestic situation, VRI (cotton covered) = grip steel conduit, as in Eric's example photo -
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What has the OP said, which might lead you to believe it might be the much more expensive installation of threaded conduit?
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Electrics after a fire
- Thread starter MickieMonday
- Start date
Domestic situation, VRI (cotton covered) = grip steel conduit, as in Eric's example photo -
.
What has the OP said, which might lead you to believe it might be the much more expensive installation of threaded conduit?
could you send us some useful pictures?
Such as:
Inside several sockets switches etc
The fusebox showing the ends of the conduits and any earth wires or clamps please.
I think most unlikely - when I've heard of TNC systems existing (and I've heard the same from two different 'grey beards' so I'm believing what I was being told*). The circuits were wired in single core MICC with the larger CSA of the sheath meaning the voltage drop on the PEN conductor was minimal. The instances were more commerial fit-out rather than industrial and it was done to save money (The idea of someone wiring something in MICC trying to save money sounds a bit silly in the modern world - but different times etc) I've heard of it being applied to both submains and also to final circuits as well. Even back then the engineer in charge had to get permission from the home office to install a PEN in a customers installation. The idea that someone would drag a drum off single core MICC off the site and start wiring mrs jones's sockets in it, with the increase in installation and termination time -No they'd just get someone to liberate a drum of twin & ecc from a more conventional job - they might actually make it to the pub on the saturday afternoon after finishing the private job.
More likely its just using the containment as earth, possibly with a fifty year DIY bodge to get past some some bad joints (possibly by someone who had heard about north amercian practices) , but no way was it intended that way
*It was never that widespread either, I'm yet to have have seen an example, despite having worked on plenty of installations wired in that sort of era, there is also the possibility that it was a localised practice or even in a number of jobs being done by the same contractor or being overseen by the same engineer.
As I'm sure you actually know, "PME" is not "another name for TN-C-S", since they relate to totally different things. TN-C-S is only allowed if PME is present.
There is also PNB (Protective Neutral Bonding).
Surely not 'totally different'.
I am still puzzled by this. Could you explain please?
You are quite probably right - but it's that equals symbol that is a guess, since there is no evidence for it.
Why not? "TN-C-S" relates to how the DNO's earth is supplied to an installation - with a two-conductor feed and the earth derived from the neutral within the installation. "PME" means that the neutral of the DNO's final distribution circuit has at least one other connection to true earth in addition to the one at the transformer/substation. They are surely very different things, afren't they?
I'm also puzzled, because I thought I was just "stating facts" ...
Any supply could be configured within the installation as TN-C-S (i.e. the installation's 'earth' could be derived from the neutral within the installation {at the cutout}) - but that is surely only 'allowed' if the supply (distribution circuit) has been PMEd?
Again, there is also PNB. TN-C-S is not always PME.
There is, but I doubt that you'd ever see that in a domestic installation (and this is a DIY forum).
There isn't really any appreciable difference between 'PME' and 'PNB'. With PME, there is at least one further connection (in addition to the one at the transformer) between supply neutral and earth in the course of the DNO's distribution cable. With PNB, there is again (just) one additional connection between neutral and true earth, but that is "at" the installation.
Hence, if there was just one additional neutral-earth connection, it would be called PNB if that connection was located 'within' the installation, but PME if it were a few centimetres before it connected to the installation - i.e. essentially 'no difference'.
There is, but I what I was writing (and have just posted) whilst you were writing that.
"PNB" is really just a subset of "PNB" (both requiring at least one 'additional N-E connection - the only difference {in the case of a single additional connection} being its location) - so one can really take "PME" to include PNB.
As you say the earth is supplied to the installation [by the neutral]. I am not sure that is classed as within the installation.
Connecting exposed and extraneous-conductive-parts to the neutral within the installation is prohibited.
So - PME is TN-C-S plus [at least] one other earth connection.
I wouldn't class that as totally different, would you?
In fact, within the installation it is exactly the same.
Presumably not.
By the DNO - but I dispute that as being within - which is prohibited.
I don't think so. If it hasn't been PMEd then it is TN-C-S.
I had this discussion ( PME v PNB ) last weekend. Found this
professional-electrician.com
Protective Earthing Systems: What’s the difference between PME and PNB? | ECA
Darren Crannis, ECA Technical Manager, looks at protective earthing systems and unravels the difference between PME and PNB. The distinctions between TN-C-S earthing variants, Protective Multiple Eart
professional-electrician.com
You appear to be quibbling, I would say somewhat 'pedantically' about the terminology, and I'm not sure why.
Well, in electrical terms that's obviously what one does - and in the cases of the bonding of extraneous-c-ps it's essentially literally what one does.
What is 'prohibited' (within a domestic installation) is connecting an exposed-c-p to a conductor which is a single 'combined N & E').
Not really. PME is PME and is a feature of the distribution network, whereas TN-C-S relates to how the installation derives its 'earth'.
The supply to my house has been PMEd but I am certainly not using the supply as TN-C-S (and, at least theoretically, could not do so unless they provided the connection to their incoming neutral).
Yes, I would.
As above, the only thing which is 'prohibited' is having conductors within an installation which are a 'combined N & E'. I think that makes sense, since it would mean that, even under non-fault conditions, exposed-c-ps in the installation would not all be at exactly the same potential.
I don't really understand what you are saying. If the supply hasn't been PMEd, then it is not 'allowed' to be used as TN-C-S
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