Earth bonding


Postby collectors » Sun Jan 10, 2010 6:05 am

Am i correct in what i have heard that only the gas/water & electric supply's need to be bonded in 10/10/16mm earth cable if a newer 17th addition twin rcd board has been fitted with all circuits being RCD controlled.
IE: No cross bonding is required on sinks/boilers/bathrooms etcetera.

Many Thanks.

Chris.
collectors
Rank: Foreman
Progress to next rank:
27.7%
Posts: 283
Joined: Mon Dec 01, 2008 7:26 am

Sponsor

Simply Build It

Postby ericmark » Sun Jan 10, 2010 5:40 pm

The 17th Edition has removed some of the requirements part of

701.415.2 Supplementary equipotential bonding says:-

Where the location containing a bath or shower is in a building with a protective equipotential bonding system in accordance with Regulation 411.3.1.2, supplementary equipotential bonding may be omitted where all of the following conditions are met:
(i) All final circuits of the location comply with the requirements for automatic disconnection according to Regulation 411.3.2
(ii) All final circuits of the location have additional protection by means of an RCD in accordance with Regulation 701.411.3.3
(iii) All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2.
NOTE: The effectiveness of the connection of extraneous-conductive-parts in the location to the main earthing terminal may be assessed. where necessary. by the application of Regulation 415.2.2.

It does not simply say it is not required. What it does say is where all the parts are bonded in other places (See 411.3.1.2) then there is no need to do it all a second time.

The 17th Edition or BS7671:2008 is quite a big book and there are cross references all through the book. On another site many Electricians have been debating the use of spurs and many seem to think these are limited to 3 meters! Also on lighting in one part it says you can protect to 16A but in another part it says manufactures recommendations must be followed and ceiling roses are rated at 6A.

So to take one part of the book and to try to follow just that small part can lead to all sorts of problems. However since bathrooms are special locations under Part P this is really only a problem for the trade as there is really no DIY in bathrooms any more.

The question must be: Why do you ask? I see no problem with bonding and simple answer is if not sure then play safe and bond which is what most Plumbers do.
ericmark
Rank: Project Manager
Posts: 1749
Joined: Fri Oct 02, 2009 8:49 pm
Location: Mold, North Wales.

Postby collectors » Mon Jan 11, 2010 4:41 am

Hi ericmark,
i am retired from the electrical work now & was just interested on comments on another forum & still like to keep up to date with things going on in the electrical world. The guides sometimes seem a bit a bit disjointed & contradicting of themselves. But hasn't that always been the way. LOL.
collectors
Rank: Foreman
Progress to next rank:
27.7%
Posts: 283
Joined: Mon Dec 01, 2008 7:26 am

Postby ericmark » Mon Jan 11, 2010 4:49 pm

Forgive me the way I replied this is a DIY forum and it is so easy to give misleading information as to regulations.
As an Electrician even if ex then you are unlikely to make errors. However tell the DIY man you don't need to bond if and he will miss out the if bit.

Main thing is must have RCD on all circuits including lights before you can use relaxed rules.

I have also heard people comment on sockets in a bathroom. These were allowed in a bedroom with a shower cubical all they have done is make the rule universal so if you remove the bed you don't need to take out sockets.

At 3 meters from zone to socket no normal bathroom can have a socket as they are not big enough but no need to limit to bedroom.

Some of the government rules are worse. In a wash room, Utility room etc. You don't need to notify work under Part P. Add a food preparation area and you have. I would have thought it was the sinks and water with high powered cookers etc which need special attention why adding a hygienic counter top means you then need to notify the council seems daft.

I would think the guy who wrote the rules never looked up was made a room a kitchen.

The 17th does have some major flaws. The main one is no one said that SELV supplies do not need RCD protection. Since separated an RCD would never work but the rules on cables buried in walls seemed to have missed this.

Once there is a flaw then one has to make up ones own mind as to what was intended.

And with bathrooms I can see it is daft to earth short isolated bits of metal work where so much is now plastic. However I have also seen copper pipe with plastic push on connectors which to me are far too short to isolate.

And common sense is not that common. It seems people no longer regard it as a guide but as law. It always seems odd to me to have a guide to tell one how to use a guide?
ericmark
Rank: Project Manager
Posts: 1749
Joined: Fri Oct 02, 2009 8:49 pm
Location: Mold, North Wales.

Postby collectors » Thu Jan 14, 2010 10:43 am

Hi ericmark, as you know your self there has been so many changes & contradictions over the years, i think it was best to just cross bond as before as i am sure they will change the rules again. I can remember many years ago where just about anything in a property was bonded, including steel door frames. But that was short lived & the ruling changed after a couple of shocks. (But not all was ELB protected back then. Sorry RCD as it is now)
Thanks for the info.

Chris.
collectors
Rank: Foreman
Progress to next rank:
27.7%
Posts: 283
Joined: Mon Dec 01, 2008 7:26 am

Postby moggy1968 » Sat Jan 23, 2010 11:47 pm

I think one reason for removing equipotential bonding was that it could, under certain circumstances introduce a risk of shock where non previously existed, which would be rather contradictory. As above, the regs don't always make sense. where there is no chance of metalwork becoming live, taking a cable to it introduces that chance in the event of a fault. BU the rules say the main bonding has to be in place, and equipotential bonding if the conditions above aren't met. I have seen this happen on a property where the main earth had come loose, while in the kitchen a back box with no grommets had chaffed a cable through. result, bathroom taps holding a potential of mains voltage just waiting for someone to touch them, which they did!! (no RCDs either)
moggy1968
Rank: Ganger
Progress to next rank:
98.7%
Posts: 198
Joined: Sat Feb 21, 2009 11:32 am

Display posts from previous
Sort by
Order by



  • DIY How to Project Guides

  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!



 


  • Related Topics