Bonding problem

[MarkP]

Hi guys. I've got a job to go to next week where the customer has had central heating installed. There is no existing bonding or supplementary in place on the boiler, gas pipe, water pipe or in bathroom. The first objective to bond the gas pipe and water pipe which appears to be straight forward. (earth block at side of cutout cable run to each). The central heating system is a bit more tricky as the plumber has done some of his runs in plastic and others in copper. This is the first time I've come across the plastic and copper combo so it's stumped me. The gas pipe from the meter appears to be a full copper run to the boiler, where as the water in and water out pipes are half and half. In the bathroom I am presented with a similar problem, the water pipes to the metal towel rail are run in plastic, but the pipes out of the floorboards are metal.

My question is where do I start?! Shall I only bond the pipes which I know are full copper runs between ie: gas meter and boiler and in the bathroom just between shower, toilet intake pipe, sink pipes and bath pipes?

Thanks for a help gents.

 

[Deleted member 9648]

You require main bonding to the incoming sevices....gas and water...on the consumer side of the stopcock. There is no requirement to main or supplementary bond heating pipes/boilers unless the boiler is outside and external pipework is coming in. Supplementary bonding may be required in a bath/shower room between conductive parts and extranuous conductive parts if....
1 There is no RCD protection to all circuits within the bath/shower room
2 There is poor continuity (> 1667 ohms) between conductive and extranuous conductive parts within the bath/shower room

Nothing else is required.

 

[MarkP]

Nice one, cheers for that

 

[Davey101]

A lot of people seem to be of the opinon that central heating pipework does not need bonding. Reg 411.3.1.2 clearly states that central heating pipework shall be connected to the MET . This question also came up on my 17th course. As I was aware of this being a Corgi requirement, but unsure of the regs, I specifically asked the question, and was told very firmly that it IS a requirement, and always has been.

I can't see anyway around bonding heating pipework, unless I have missed something. Another point is that the plumber will most likely mention the requirement for an earthing conductor, your client may not be happy that you have not installed one.

 

[Sintra]

Main Protective Bonding Conductors
All extraneous conductive parts in an installation must be connected to the main earthing terminal by main protective bonding conductors. This applies to the metallic sheath of a telecommunications cable where permission from the owner of the cable must be obtained. 411.3.1.2
For TN-S or TT systems the csa of main protective bonding conductors must be a minimum of 6mm and not be less than half the csa of the main earthing conductor. 544.1.1
For a PME system the csa of the main bonding conductors must not be less than that given in Table 54.8 ie a 10mm protective bonding conductor for a neutral conductor of 35mm or less. 544.1.1
For a service pipe, the main bonding conductor should be connected as near as possible to the point where the service enters the building. The connection must be before any branched pipework and on the consumers side of any meter. If possible the connection should be made within 600mm of the meter outlet. Where the meter is outside, the bonding connection should be made at the point of entry of the service into the building. 544.1.2
Main bonding conductors should not be supported by the service pipes they are connected to. 543.3.1
Where a main bonding conductor loops in and out to connect to an extraneous-conductive-part, the conductor should be unbroken at the connection. 528.3.3
It is not necessary to run a main protective bonding conductor to an incoming service where the incoming service pipe and the consumers pipework are both made of plastic. If the incoming service pipe is made of plastic and the consumers pipework is made of metal it is recommended to main bond any metal pipework. OSG p29
Supplementary Bonding Conductors
Supplementary bonding is not required in a bath or shower room if all the extraneous conductive parts of the installation are connected to the main equipotential bonding. p6, 701.415.2
It is not generally required to supplementary bond the following :kitchen pipes, sinks, draining boards, metallic kitchen furniture, boiler pipes, metallic parts supplied by plastic pipes or metal pipes to hand basins or wc's ( excluding metal waste pipes in contact with earth ). OSG p31

 

[Davey101]

Reg 411.3.1.2 also clearly states that heating pipework needs bonding.Page 27 of the OSG also clearly states the need. Every large job I've run/worked on in the past few years has also had an earth run to pipework, ducting etc, although designers arent always right

There seems to be a contradiction in the regs regarding this, unless there is something simple I'm missing. Anyone got an actual answer?

Edit- There is a simple answer, one reg says connection of a main protective conductor , the other is talking about supplementary bonding (I really must concentrate more). So, presumably you have to run an earth to the flow and return pipes at the boiler, but you dont have to cross bond loads of pipes in a plant room, or pipes in an airing cupboard etc.

 

[Deleted member 9648]

QUOTE A lot of people seem to be of the opinon that central heating pipework does not need bonding. Reg 411.3.1.2 clearly states that central heating pipework shall be connected to the MET . This question also came up on my 17th course. As I was aware of this being a Corgi requirement, but unsure of the regs, I specifically asked the question, and was told very firmly that it IS a requirement, and always has been.

I can't see anyway around bonding heating pipework, unless I have missed something. Another point is that the plumber will most likely mention the requirement for an earthing conductor, your client may not be happy that you have not installed one QUOTE


Regulation 411.3.1.2 states EXTRANEOUS CONDUCTIVE PARTS require main bonding.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". A central heatng system within the confines of the equipotential zone is not liable to introduce an earth potential and therefore is not an extraneous conductive part and will not require main bonding.Only if parts of the system are external and metallic pipes are coming in from outside would main bonding be required.

The definition of Extraneous conductive parts is the key to understanding the requirements of 411.3.1.2


Edit.... I have been part of an NIC approved contractor for 20 odd years and in that time I have only ever main bonded a handful of heating systems, with pipework extending outside the equipotential zone . The vast majority of normal heating systems have not been main bonded. In that time we have had four different inspectors come annually to inspect our work and never have any of them picked up a lack of main bonding to heating systems....because for the reasons above it normally is not required.

 

[Davey101]

Wirepuller, I noted that the reg refers to extraneous conductive parts. I can't see how metal pipework, especially connected to an electric boiler and potentialy running in close proximity to T+E cables would not be classed as such.

For what its worth, I've never pulled an earth from the MET to the boiler/pipework in a house either, although, as I've said its pretty much mandatory on larger projects.

Cheers, Dave.

Edit- just rechecked definitions of 'extraneous conductive part', and it is more specific than I realised, stating that it must be 'connected to the mass of earth', so, er maybe heating pipework isnt classed as 'extraneous', although bearing in mind that the pipework has a good chance of being in contact with the fabric of the building, seems strange to me.
Learn something new everyday I guess.

 

[Deleted member 9648]

Hi Dave,
Like I said we've been having annual NIC inspections for twenty plus years and they've never picked up on no main bonding to heating systems entirely within the building..(as most are). I guess i'ts up to the individual...spec...or customer,if they are happy to pay for it I'd be happy to bond it but I'm not going to price in unnessesary work if they dont ask for it.
Had a related experience a while back on a refurb....builder asked why I hadnt bonded the steel sink in the new kitchen he was in the process of installing,I explained that it isnt required and it is only down to a persistant myth that you still see it done. Next thing he produced the box that the sink was supplied in which had in big bold letters on the side....WARNING,THIS SINK MUST BE EARTHED......What chance have you got?
Have you noticed as well that when electrical issues like this crop up the client always seems more inclined to take on board the opinions expressed by the builder/plumber/gardener rather than the sparks who's only been doing it 30 years ?

 

[Davey101]

Yeah, I know what you mean mate, a little knoweledge and all that eh?
It also doesnt help when the lecturer running your course tells you one thing, and everyone else tells you something else, or when guidance notes and books list heating pipes as 'extraneous conductive parts'. Just one very small point- what about underfloor heating pipes? These are connected to the 'mass of earth', any thoughts?

I'm going to start a thread- 'What I found out I didnt know today'.