Another couple of main and supplementary bonding questions!

FX · 11 Nov 2009

Hope someone maybe able to help with these queries.

Main Bonding Incoming water main is in mdpe coming into the kitchen. It then has a copper stop tap and runs for about 2-3m in copper, mainly behind units, apart from top half metre as it enters into the loft (single storey). At this point it becomes Hep20 plastic and remains so throughout the house. Does this piece of copper pipe require bonding?

Supplementary Bonding In bathroom. Central heating pipes run as Hep20 plastic under floor and then tails above floor to towel rail are chrome plated copper (100mm ish). All domestic water pipes are in Hep20 plastic. The bathroom has ELV downlighters, a shaver socket and an ELV extract fan set into the wall (transformer located in loft above). All these are served by the same lighting circuit. There are no other electric points or services in the bathroom. Is supplementary bonding required?
NB the lighting ring is served by a 6A MCB and an 80A 100mA RCD. (TT installation)

Can you explain why even if the answers are no. Many thanks[/u]

bongos · 11 Nov 2009

FX said:
Main Bonding Incoming water main is in mdpe coming into the kitchen. It then has a copper stop tap and runs for about 2-3m in copper, mainly behind units, apart from top half metre as it enters into the loft (single storey). At this point it becomes Hep20 plastic and remains so throughout the house. Does this piece of copper pipe require bonding?

Main Protective Bonding

FX said:
Supplementary Bonding In bathroom. Central heating pipes run as Hep20 plastic under floor and then tails above floor to towel rail are chrome plated copper (100mm ish). All domestic water pipes are in Hep20 plastic. The bathroom has ELV downlighters, a shaver socket and an ELV extract fan set into the wall (transformer located in loft above). All these are served by the same lighting circuit. There are no other electric points or services in the bathroom. Is supplementary bonding required?
NB the lighting ring is served by a 6A MCB and an 80A 100mA RCD. (TT installation)

Supplemental Bonding

Have a read of the links. At a guess I would have thought you should still run a main protective bond to your copper section of water pipe incomer in the kitchen.

As for the supplemental bonding - don't know! It would normally be required due to no 30mA RCD protecting the bathroom circuits but it doesn't sound like you actually have any extraneous conductive parts in the bathroom!

Aside from this, it would be a very good idea to add 30mA RCD protection to your installation anyway, especially as you are on a TT setup

FX · 11 Nov 2009

bongos";p="1402732 said:
FX said:

Have a read of the links. At a guess I would have thought you should still run a main protective bond to your copper section of water pipe incomer in the kitchen.

As for the supplemental bonding - don't know! It would normally be required due to no 30mA RCD protecting the bathroom circuits but it doesn't sound like you actually have any extraneous conductive parts in the bathroom!

Aside from this, it would be a very good idea to add 30mA RCD protection to your installation anyway, especially as you are on a TT setup

Click to expand...

Hi Bongos........

Could you explain your rationale for bonding the water pipe?

Anyone else?
Just for clarity the the sockets (plus others) are protected by a 30mA RCD.

ricicle · 11 Nov 2009

If you look in to the physics of why a metallic pipe entering a property/zone needs to be bonded then it is clear that a copper pipe that does not enter from outside will not need bonding.
It is up to you the designer to state your reasons for not doing so.

bloxy · 11 Nov 2009

ricicle said:
If you look in to the physics of why a metallic pipe entering a property/zone needs to be bonded then it is clear that a copper pipe that does not enter from outside will not need bonding.
It is up to you the designer to state your reasons for not doing so.

Can you clarify then?

Most houses since the 70s will have black or blue plastic water mains entering the property and then maybe going to copper but I believe we are told that there must be main bonding of the copper within 600mm from where the service enters and the copper starts.

If I have a plastic water main then there is no route for a potential to enter from outside even if the rest of the house is plumbed in copper is there?

Gas is different because the plastic main can't enter the property and has to change to metal outside, an outside potential could be introduced, so it needs bonding?

Oil? Well my oil enters the boiler house in copper but then goes to a rubber hose to the boiler(no steel braid) and the boiler has copper going from the boiler house to the main house but the two are separated by the rubber hose. There is no point where a potential could be introduced from the oil pipe to the metal work of the house. So should the oil feed be bonded when it enters the boiler house?

ricicle · 11 Nov 2009

All new properties which are fed with water/gas in plastic out of the ground are still bonded generally in 10mm² but as I said above if you know the correct reason for bonding these and can justify your reasons for not bonding because you know they cannot introduce a different earth potential fron outside then why bond ?

bloxy · 11 Nov 2009

So in the three scenarios I gave what should be bonded and what need not be bonded? (just trying to increase my understanding)

barcelona · 11 Nov 2009

No and no.
See here. http://www.blogcdn.com/www.cinematical.com/media/2007/11/joker113007.jpg

FX · 11 Nov 2009

If you look in to the physics of why a metallic pipe entering a property/zone needs to be bonded then it is clear that a copper pipe that does not enter from outside will not need bonding.
It is up to you the designer to state your reasons for not doing so.

According to the definition I have of Main Eqiupotential Bonding or Protective Eqiupotential Bonding) it states that
MEB conductors are required to connect the following metallic parts to the MET, where they are extraneous conductive parts
The definition of an extraneous conductive part is
A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation.
I would suggest that a piece of copper tube isolated by plastic tube is no more an extraneous conductive part than a kettle, door handle, metal chair, taps etc[/b][/i][/quote]

bongos · 12 Nov 2009

bloxy said:
Most houses since the 70s will have black or blue plastic water mains entering the property and then maybe going to copper but I believe we are told that there must be main bonding of the copper within 600mm from where the service enters and the copper starts.

This was my thinking - the water pipe can't introduce a potential from outside but I thought that the copper section just inside the property would commonly have to be bonded. But as ricicle says, if you can justify your reasons then I suppose you might not need to bond this short section of copper in this case.

FX · 13 Nov 2009

Looking at it another way, is this section of copper tube any different from a pair of taps in a cloakroom if the water supply is MDPE and the house is plumbed in Hep20 and then metal taps at the basin. Surely, these are equally liable to introduce a potential?

ricicle · 13 Nov 2009

FX said:
Looking at it another way, is this section of copper tube any different from a pair of taps in a cloakroom if the water supply is MDPE and the house is plumbed in Hep20 and then metal taps at the basin. Surely, these are equally liable to introduce a potential?

How would they introduce a potential. They couldn't if there is no metallic connection to an outside zone.

bernardgreen · 13 Nov 2009

ricicle said:
How would they introduce a potential. They couldn't if there is no metallic connection to an outside zone.

Pure water does not conduct electricity so in a non conductive plastic pipe pure ( as in distilled ) water will not introduce a potential and more importantly will not provide a path for fault currents that could be passing through a human body.

The water supplied in the domestic mains is not pure, it has dissolved salts, minerals from its source and other chemicals are added to ensure it is biologically safe. Therefor it is NOT an isulator and will carry current, water in a 15 mm diameter pipe will carry enough current to provide a fatal shock at 230 volts.

bongos · 13 Nov 2009

bernardgreen said:
ricicle said:

How would they introduce a potential. They couldn't if there is no metallic connection to an outside zone.

Click to expand...

Pure water does not conduct electricity so in a non conductive plastic pipe pure ( as in distilled ) water will not introduce a potential and more importantly will not provide a path for fault currents that could be passing through a human body.

The water supplied in the domestic mains is not pure, it has dissolved salts, minerals from its source and other chemicals are added to ensure it is biologically safe. Therefor it is NOT an isulator and will carry current, water in a 15 mm diameter pipe will carry enough current to provide a fatal shock at 230 volts.

True but for this to happen surely there would have to be metal pipe out in the road (for example) of one potential before turning to plastic pipe and entering the house and then carrying this initial potential in the actual water within the plastic pipe to where it would rejoin metal piping and reitroduce this potential to the metal pipework.

Surely not likely (in practice at least)?

Edited (now probably makes even less sense)

bernardgreen · 13 Nov 2009

The potential the water brings in may be from the pipe work in adjacent houses. Normally this should be ground but if one house has an earth fault such that its pipe work in not at ground potential then other properties could be affected via the water in the network pipes.

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Another couple of main and supplementary bonding questions!

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