Main bonding to services.

[juniorspark]

hello to all, just recently i have started to be sent out to carry out works on my own (recently completed my jib) and have now moved up from apprentice, however there is some grey areas that im struggling to understand and would like to give some scenarios ive recently come accross and can not get a definate answer too all regarding main bonding to water.

1. stop tap is in bathroom and is copper but new bathroom fitted and pipework in bathroom is plastic, shaould i main bond at the first available part where it returns to copper wether that be in the same room or not?

2. if there is a mixture of copper and plastic pipes and i main bond to the first copper part then of what use is this if it is then interrupted by plastic pipe before returning to copper.

I read a simmilar story to this on another forum but no one seems to give a definative answer.

thank you for any help in clearing up this confusion for me, i understand the reason and theory behind main bonding but the confusion lies where plastic and copper is involved.

 

[Tipi]

The way I understand it is that by bonding all the incoming services together there is no possibility of a potential difference between them. So, if a fault occurs, it will go to earth and there is no danger from touching an extraneous conductive part as it too will be at earth potential. Copper pipes in bathrooms etc should have supplementary bonding unless the conditions in reg 701.415.2 are met

 

[sparkytim]

Hi

Yes it can quite daunting to be out there on your own now and have to make all the decisions.

I have found it helps to get clear in mind what Bonding is for.

In simple terms this is how I understand it

It is EQUIPOTENTIAL BONDING, that means its purpose is to create and ensure an EQUAL POTENTIAL on exposed Metal work to minimise the shock risk. If two parts are at a DIFFERENT potential then that means there is a POTENTIAL DIFFERENCE between them i.e. PD= VOLTAGE, touching them both at the same time will result in a persons body acting as a conductor and current flowing thru it that is a SHOCK.

If a fault has occured that has put a large Voltage onto the Electrical system earthing then there could be a LARGE potential difference between it and other earthy metal work IF NOT BONDED, with fatal consequences

So we have an Earth POTENTIAL coming into the building on the Electricity supply cable say 0 Volts, ALSO coming into the building is a Metal Water pipe maybe at 10 Volts, if a person touches the Water pipe and the Electrically Earthed metal case of the washing machine he/she will get a shock.

IF we connect a BONDING conductor BETWEEN the Electric Main Earth terminal and the Pipe where it comes INTO the building then we make them the same POTENTIAL and therefor reduce the likelyhood of a shock.

So coming back to your question if it is a service coming into the property that can introduce an earth Potential then we Bond it AT the point it COMES in

Many houses now have an Alkathene NON conducting pipe coming in. If this connects onto some Copper pipework then yes Bond at that point, IF it is ALL plastic internally EXCEPT for SHORT pipes up to a sink or radiator etc, then NO it can not introduce an earth Potential INTO the property.

I dare say there will be further comments from or other learnered friends

 

[juniorspark]

so would you say that main bonding connected at the first possible place, or to be ommited and install supplemntary bonding only or both - im struggling with this , i understand the reasons behind both main and supp but putting into practice in certain installations is proving more awkward.

 

[sparkytim]

Yes MAIN BONDING ONLY required at ENTRY to building,

Supplementary Bonding as has been said is now NOT NORMALLY required if the Installation meets 17th Edition.

i.e. Main Bonding in place IF required

ALL CIRCUITS INTO BATHROOM RCD protected as required

and max DISCONNECTION times met to Table 41.1

See brb pG 46 and Pg 166

 

[juniorspark]

Yes MAIN BONDING ONLY required at ENTRY to building,

the stop tap is copper (no where to fit a clamp, then pastic until it resurfaces in another room as copper again, would you clamp where it reurns to copper even though this is not where it enters the building?

 

[sparkytim]

Depends

How far does it then go in copper?

If it is just a short length in free air then onto Plastic around the house then NO I would not, BUT OTHERS WOULD it won't do any harm IF you do.

If you are not sure then Do IT, better to have it when NOT really required then NOT HAVE it when it is.

There will be plenty of decisions like this to make, get the PRINCIPLE in mind and you will be able to make sensible decisions, If You just Wan't RULES then there are not enough of them to cover EVERY situation.

 

[juniorspark]

very helpfull info thank you.

I have decided that as i cant bond at the stop tap as there is no where to fit the clamp, then the next best place is where it resurfaces which is next to the combi boiler where the gas meter is also earthed.

If i then run a wander lead from my earth water pipe next to combi to say pipes under sink in kitchen i should expect to see a negligable resistance proving the rest of the pipework within the property is effectively connected.

 

[sparkytim]

Sounds a good plan, but if you get a very HIGH reading when testing to pipework in the bathroom i.e. > 299 M ohms, then that would mean it was segregated by plastic pipework maybe. This WOULD BE OK, because it would not introduce an earth Potential into the bathroom.

If the requirements were not met of 701.415.2 so that supplementary bonding IS REQUIRED (i.e. an existing installation with NO RCD protection to the lighting inside the bathroom), then you would have to provide supplementary bonding INSIDE the bathroom inter-connecting ALL Metal Pipes and CPC of lighting circuit, shower or other CIRCUITS if any.

This would NOT have to be taken back to the MET as some seem to do as you only need to provide SUPPLEMENTRY BONDING

 

[rainydays]

on a similar note, if the stop tap was in the bathroom and you could get a bond to it, then would you take it to this location as it would just be like taking a supplementary back to the M.E.T would it not

 

[sparkytim]

Yes in that case the MAIN BONDING connection would just happen to be in the bathroom if this was the MAIN stop tap at the supply point coming into the building.

 

[rainydays]

What i mean is, from previous post you do not take supplementary bonding back to the main earth terminal.

But if you take your main bonding to the stop tap in this location are you not creating the same scenario

 

[sparkytim]

Again what is the principle here?

The idea is to provide ADDITIONAL PROTECTION because of this areas special risk, i.e. naked wet people touching a metal radiator and Bath tap at the same time.

So SUPPLEMENTARY bonding IF required provides EQUAL POTENTIAL to all metal things that could be touched and reduces the shock risk.

---------- AUTO MERGE Post added at 15:40 ---------- Previous post was at 15:32 ----------

Its not a problem IF you do have interconnection back to the MET but it is NOT required to have it, IF its not there because of plastic pipe segregating it.

Just think of another situation TNCS supply earth segregated at entry to an Out-building, TT for outbuilding but it has a Water supply from house run in Plastic then on to copper pipe in outbuilding.

What do you do? you BOND THAT metal pipe to TT earth MET

No need to Bond back to MET in house.

 

[Manator]

Now thats what this forum is all about !

Thank you sparkytim.

 

[juniorspark]

i agree very helpful direct response, i understand the theory and know what and why things need to be done but in the real world certain situations prove a little more difficult.

many thanks much appreciated