BATHROOM SUPLEMENTARY BONDING


Postby DAVENPORT » Fri Aug 27, 2010 3:48 pm

HI ALL
I HAVE A GOOD MAIN BONDING FROM THE BATHROOM COLD WATER MAIN FEED PIPE TO THE C U
I HAVE NO CROSS BONDING IN THE BATHROOM
I AM FULLY RCD PROTECTED

AN ELECTRICIAN WHO I KNOW AND RESPECT TELLS ME THAT I DO NOT NEED
CROSS BONDING IN THE BATHROOM IF I HAVE R C D s IN THE C U

ALL THE COMMENTS I READ SEEM TO SAY I DO NEED CROSS BONDING ??
GLAD TO HEAR YOUR COMMENTS

JAYS
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Postby stoneyboy » Fri Aug 27, 2010 9:44 pm

DAVENPORT,
I would suggest that if you have an installation totally carried out under the 17th then you can get away with no bonding.
Whilst you may be RCD protected do you test their operation regularly as the instructions specify? RCDs can get sticky and may not operate under fault conditions.
Unless it's going to give you a lot of problems I would recommend you fit the bonding - it won't cost a lot for materials and you can DIY, certification is not needed.
end
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Postby ericmark » Fri Aug 27, 2010 10:01 pm

701.415.2 Supplementary equipotential bonding states:-
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.

So he is correct. OK why do we bond anything! The idea is to keep everything as the same voltage not really worried what voltage as long as it is the same. Idea of birds on power cables. The problem was that if something goes wrong in one place for example the airing cupboard with a faulty immersion heater it can move that fault to another room for example the bathroom and if one was to touch the hot water pipe and the radiator one could get a shock.

However with the use of plastic pipes bonding could just as easy transmit the fault as protect against it and careful consideration had to be given as to if the cross bonding made things safer or more dangerous and so it was considered that if some other protection could be used like a RCD this would remove the danger from fault transmission without possibly introducing other dangers so the new 17th Edition (BS7671:2008) removed the need to cross bond and required 30ma RCD's which will trip is 40ms or less instead.

This then still give protection where plastic and metal pipes are used. Because metal pipes look better than plastic they have been used where the pipe work can be seen but then plastic used where hidden. Although in industry we have used plastic pipes for many years with air pressures of over a 100psi it seems plumbers have been having problems with water. In the main it is their attempt to make them neat and lack of pipe clips so expansion and contraction can in time allow them to pop out. Also different makes used different thickness and insert types and sizes and it seems mixing makes also causes a problem. As a result some insurance companies don't like plastic and there seems to be a battle going on as to if to use plastic or not.

All this has resulted in some odd mixtures with plastic couplers on metal pipes meaning the separation is too short to electrical isolate but long enough to stop the current to flow that would trip a MCB and many cross bonded system has as a result lost it's bonding.

All down to a risk assessment and with RCD protecting all circuits the risks of having no cross bonding are considered to be acceptable.
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Postby DAVENPORT » Sat Aug 28, 2010 5:47 pm

THANKS A LOT FOR THE REPLY ON CROSS BONDING
I AM SURE MY RCD INSTALLATION GIVES ME THE REQUIRED PROTECTION
HOWEVER IF I WENT FOR "BELT AND BRACERS" IN THE BATH ROOM
AND DID CROSS BOND MIGHT I BE INTRODUCING A UNNECESSARY RISK ??
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Postby ericmark » Sat Aug 28, 2010 11:57 pm

Unlikely I would still cross bond.
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Postby buzbydiy » Sun Feb 06, 2011 1:01 pm

Just picking up from Davenport's question about bonding. I have gutted our bathroom at the moment, and am at the stage where pipes are accessible. When I stripped the old suite out - there was bonding on the radiator by means of a clamp at the bottom of it ..... as well as cross bonding on the hot & cold of the basin. Nothing on the bath.
My main questions are - as I am at a stage to do something about it is:-
1. How 'extensive' do I bond pipework. I presume I need to cross bond hot & cold of bath & basin & cold feed for the toilet where they are out of the floor.
I am fitting a chrome finished towel warmer, [ not electrically heated ]. Though it said nothing in the instructions will I have to put a clamp say on one of the rungs, and will I also need to bond the supply and return pipes to it as well. In other words. Would I need three points of bonding ? ? ?
2. I will have a ceiling light that has a chrome finish, and a Shaver socket in the room. Do I need to run a seperate 4mm earth lead from these appliances to a pipe within the bathroom, or is the electrical earth sufficient ? ? ?
An additional question if I may. I am fitting a thermostatic bar valve shower unit on the wall above the bath, [ so bath can be used as a shower ] which has its hot & cold tee'd off the bath hot & cold. Will bonding the shower beyond the 'tee' - be enough to bond the chrome bar valve. Distnce from tee to valve is 4ft, or do I have to bond the bar valve as well.
I don't mind what ever I need to make my family safe, but could do with some clarity please.
Regards,
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Postby ericmark » Sun Feb 06, 2011 9:47 pm

It would have been better to have started a new post as many ignore posts which already have a number of replies.

With the RCD and plastic pipes the whole idea of bonding has needed revising. With a radiator fed with plastic pipes the bonding could make it more rather than less dangerous. And since it is often impossible to tell if any plastic has been used the safe method now required in the regulations is to have every item including lights in a bathroom supplied through a 30ma RCD.

However where a RCD is not fitted doing a risk assessment then one would still come down on the side of bonding all metal.

However do remember the idea is to ensure all items are the same voltage not necessary earth voltage. So bonding means all metal parts connected together not connecting them to the main earth.

In practice since likely the shower will be connected to main earth and that will in turn be bonded in real terms everything is connected to main earth.

The wires unless part of a cables need to be at least 4mm.

In my bathroom loads of plastic pipes. (Far safer) And RCD on all circuits. So no bonding.

In spite of what people say about water and electric a length of one foot of plastic pipe even though filled with water is a good insulator. The problem is where a plastic fitting is used on copper pipe. Here you may only have an inch between the two metal parts. This means not enough current will flow under fault conditions to open a MCB and make it safe. Hence why we used RCD's.
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Postby Kevin Davies » Sat Apr 16, 2011 8:36 am

stoneyboy wrote:DAVENPORT,
I would suggest that if you have an installation totally carried out under the 17th then you can get away with no bonding.
Whilst you may be RCD protected do you test their operation regularly as the instructions specify? RCDs can get sticky and may not operate under fault conditions.
Unless it's going to give you a lot of problems I would recommend you fit the bonding - it won't cost a lot for materials and you can DIY, certification is not needed.
end


I have fitted RCDs foor many years and have NEVER known one to stick in fault..

As for OP. Your main bonding for water should not be from bathroom unless your supply pipe enters bathroom from outside.

If your bathroom circuits are protected by RCD and any circuits in walls and ceiling adjacent to bathroom are similarly protected you don't need sup bonding in the bathroom.

Pre 17th edition you actually should not have had any lighting circuit on an RCD by the way!
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Postby Kevin Davies » Sat Apr 16, 2011 8:48 am

DAVENPORT wrote:THANKS A LOT FOR THE REPLY ON CROSS BONDING
I AM SURE MY RCD INSTALLATION GIVES ME THE REQUIRED PROTECTION
HOWEVER IF I WENT FOR "BELT AND BRACERS" IN THE BATH ROOM
AND DID CROSS BOND MIGHT I BE INTRODUCING A UNNECESSARY RISK ??


You would be breaking the law. ALL works in bathroom are notifiable. They may not be classed as Minor Works. You must either be competent to BS7671, carry out all tests and give them to Building Regs or BS7671 and part of an approved self cert scheme

YOU WOULD NOT MESS WITH GAS SO WHY MESS WITH ELECTRIC? FAR MORE PEOPLE ARE KILLED WITH ELECTRIC EVERY YEAR THAN WITH GAS ...

THESE REGS ARE DESIGNED TO STOP people KILLING THEMSELVES AND OTHERS. Some people just COPY AND PASTE SECTIONS OF BS7671 AND THEN OFFER UNTRAINED AND OFTEN DANGEROUSLY INCORRECT OPINION AS IF IT WERE EXPERT FACT!!

EVEN WHERE THE ADVICE IS FACTUALLY CORRECT IT CAN BE MISLEADING IF NOT SEEN IN THE ENTIRE CONTEXT OF BS7671.

STOP MESSING WITH ELECTRIC..... IT KILLS.... EVERY DAY!!!!!

YOU WILL NOT LIKE THIS POST BUT IT IS THE BEST ADVICE YOU WILL EVER GET!

Please PAY AN ELECTRICIAN!!!!
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Postby ericmark » Sat Apr 16, 2011 5:43 pm

I have come across many RCD's that either did not trip or have tripped too slow. Many were not in domestic premises but some were. Where moulded breakers are used the trip electronics and current transformer are often not built into the breaker so can be wired incorrectly.

The lighting in my bathroom has been supplied vie a 30ma 40ms RCD since 1992 when I fitted two RCD's one to each consumer unit.

Nearly all TT supplies I have visited have had the bathroom supplied vie a 100ma delayed RCD and I have found much confusion here as the owner has read that RCD protection is required and feels it is provided. It has taken some time to explain he needs a 30ma @ 40ms RCD and the 100ma RCD is only for fire protection not for personal protection.

The other point is the "Test" button does not test the time taken and also does not complete a complete test for current. It is possible for a fault to mean either the RCD trips when it should not or will only trip on pos or neg and not on both. The tests on an RCD are done 6 times.
Twice pos and neg to show it will not trip at under 1/2 rated value.
Twice pos and neg to show it will trip at rated value.
Twice pos and neg to show it will trip in 40ms at 5 times rated value.

As well as faulty RCD's I have also found by-passed RCD's where some one has I would assume put in a temporary link and forgot to remove it after testing. The RCD meter will pick this up but test button still often works.

After two months likely this post is no longer being monitored but I have been picked up a few times for making general statements which are not true in all cases. It is very easy to forget TT supplies when working in an area with nearly all TN-C-S supplies and as a result give wrong advice.

Ordinary persons should not have access to variable RCD's however it is common for hire generators to be fitted with them. On a DIY site should we assume we are talking to ordinary persons in the UK? I have raised Part P a few times then found not a domestic premises or in Scotland.

I find the question "Is it OK to xxxx" hard as in nearly every one there will be some exception to the rule. Don't know what others charge but to plug in a RCD tester and press the button 6 times is not hard and I would not think any electrician would charge over the minimum charge for doing it?
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