I've just Persaud-ed John Rumm's piece from the thread 'Earth Bonding' into a brief article on the wiki:
- posted
15 years ago
I've just Persaud-ed John Rumm's piece from the thread 'Earth Bonding' into a brief article on the wiki:
Shall we add:
Conductor sizes and clamps required a list of things that do not require bonding but are often incorrectly assumed to be in need of it? (Kitchen sinks etc)
If appropriate, I would like to see each of the different incoming mains earthing schemes described, together with the implications of each for consumer wiring and earthing/bonding. This is something which I've never totally got my head round, and having it described in the Wiki would be great.
It's currently in the FAQ.
Not sure if the implications of different earthing schemes are perhaps better dealt with in the articles describing things that are affected - e.g. the taking electricity outside article talking about implications of exported earths with PME earthing. I can see pros and cons. Perhaps a little duplication would not be a bad thing in this case.
A nice helpful article.
A few details to chew on - I'm putting them here as some I'm sure are best discussed first.
h to a safe level (under 50V typically) during the fault.
TT earthing is unable to limit V rise to 50v, and TT is no rarity. Also some older non-TTs fail to limit to 50v.
suggestion: (under 50v for some installation types) or (under 50v in many cases)
suggest: taps would expose one to a 230V potential difference, causing a risk of electrocution.
There are a few reasons why its a risk rather than a cert.
voltage (230V) under fault conditions, but touching both exposes one to zer= o volts of potential difference.
Its often said, and theres a valid point in there of course, but i'm not convinced its actually true. A wet person standing on a concrete ground floor is surely liable to experience a painful pd between taps and floor.
ch as the earth wires of any circuits feeding power into the room as well a= s metal plumbing) are securely connected together and there are no conducti= ve items or surfaces connected to earth.
Conductive items or surfaces connected to earth are not a problem in such a scheme, as long as they're bonded. And this is normal. The fact that equi bonding is in practice normally earthed is perhaps one of the reasons for popular confusion.
If we take it a step further, equi bonding also (often but certainly not always) is effective where an earthed bathroom item is _not_ part of the equi bonding, for the reason that under fault conditions the rise of pd between the equi bonded and the earthed items isnt high enough to cause a nasty. Even with a TT install this is usually the case, since almost any fault causing a rise in V on the equi would also cause the same V rise on the earthed item - not in 100% of cases but normally yes.
It may also be worth mentioning the various arguments against equi bonding - and bear in mind the 17th is significantly relaxing the requirement for equi, so its pretty relevant if one wants to understand it properly.
otective conductors of any circuits that are included in the equipotential = bonding.
=2E.. or more often via copper pipes
NT
a safe level (under 50V typically) during the fault.
Hence why additional protection (RCD) is required...
I would expect a solid connection between mains and earth across the hands would be fatal in the vast majority of cases.
voltage (230V) under fault conditions, but touching both exposes one to zero volts of potential difference.
Not often you have a bare concrete floor. Normally there will be tiles, or carpet, or vinyl, or cork etc.
as the earth wires of any circuits feeding power into the room as well as metal plumbing) are securely connected together and there are no conductive items or surfaces connected to earth.
Yup, true. Although its not a requirement that is is. It works just fine without.
I think the 17th recognises the complexity if the concept and funds ways to make it a non issue.
protective conductors of any circuits that are included in the equipotential bonding.
well both if done right...
clear on.
For example, in a wash basin. The hot tap is supplied via copper pipe & fittings. The cold is supplied via copper pipe & a plastic tap connector. The bonding isn't now continuous?
If the plastic tap connector were replaced by one of the metal braided flexible tap connectors
Forgot to add - would things be OK as long as both taps were bonded in the same way?
Assuming that the copper pipes supplying the hot and cold are bonded together (this is usually done behind the pedastal) then it does not matter if the pipes are supplied by plastic connectors or not. The supply to the taps is now potentially balanced and there is no way either if the taps will be at a different voltage each other. If one tap is supplied by a plastic connector and is insulated from the pipe then it would not be an exposed conductive part and so would not need bonding. If the the tap is not insulated from the pipework (copperpipework all the way) then the bonding is already complete.
Adam
--8
On a slightly less serious note, I bet the wiki would get more hits if you changed the title to earthing & bondage
NT
Yup, that seems to read quite well...
I wonder if it is worth including a note somewhere about the extra significance of bonding in PME installations (with regard to disconnection of a suppliers PEN conductor in particular - which is probably a more likely real world danger for users with overhead supplies and PME)
I have to disagree. Main bonding is there to ensure that the incoming services (or any extraneous conducive part such as structual metalwork) is at the same potential as the suppliers earth or on a TT system the owners earth.
A metal incoming water supply will be at earth potential. There is no need to bond it to the CU to make it an electrical earth potential. The reason for main bonding is in case of a problem with the incoming supply. For example if the earth from the supplier was to become live then all the metalwork in the sockets, switches, washing machines could become live. Main bonding will bring all the earthed points (the extraneous condutive parts) up to mains potential as well so that you cannot touch an earthed stoptap etc and a now live metal lightswitch.
There way well be an extraneous condutive parts in these special locations. These would have to be protected under the main bonding though. Stop taps in bathrooms are not uncommon.
Just my opinion. Not a dig at your work.
Adam
Should say "Not a dig at your work on the article you wrote" :-)
Adam
Maybe, but perhaps it should go in the Types of Earthing article (I also excised some lines of NT's to the discussion page with a suggestion they should go in that article too.)
Well you could read "at the electrical earth potential" as meaning that, but it could do with clarifying if that's what it does mean. TBH I dodged that issue as I'm not sure that is the reason: I just know one's got to do it!
What you say makes sense and I'm inclined to agree with your analysis, but I'd like to see chapter and verse from the regs or suchlike, not just your or my interpretation/opinion, so I know what's going in the article is gospel[1]
True, but in that case you have main bonding *and* supplementary bonding in the bathroom, and your eqipotential bonding is also earthed. I don't see any contradiction.
[1] or true, as the case many be ;-)
Purlease, nooooo - don't set the hot pr0n site spammers off again ;-)
The regs tell you what needs to be done not why they need to be done. Your main bonding part is virtually reg 413-02-02 of the 16th edition. It tells you what needs/may need main bonding. My query was with your statement "This ensures that (metallic) gas and water installation pipework running through a building are at the electrical earth potential." Maybe a more constructive suggestion would be "This ensures that all extraneous conductive parts such as (metallic) gas and water services entering a house are at the same potential as the suppliers earth"
You supplementary part uses the term extraneous conduvtive part instead of exposed-condutive part. I will re read it later with suggestions. It looks good though.
Adam
"as the electrical system's earth" may be better (to account for TT systems)
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