Bonding a boiler

[Paul Barker]

Now we aren't talking about special location here, I mean boilers in non special locations. Most local earthing arangements are PME, and tails are 16mm so Main eq bond sb 10mm.

All local sparkies give me a different answer on this one. Most of us gas fitters now are using 10mm and doing every copper pipe, and if practical taking it to the MET if not, just to the cpc of the doublepoleswitchedfusedspur.

If customer has a sparks on site I usually ask him to do it, one guy just bonded two pipes in 4mm and took it nowhere. Most of them agree on 10mm but not all take it anywhere, especially not to MET.

bs7671:Note2 2004 states 413-02-02 (iv) that central heating and air conditioning systems is part of the main equipotential bonding.

I would read that to mean that it is same size as gas and water service conductor and like them should go to MET and be seperate conductors or have no breaks.

BUT this indicates that only the flow and return pipes are to be bonded and not necessarily directly underneath the boiler, as long as it is copper pipework throughout the clamps could be placed in a more convenient part of the system.

Any thoughts / rulings from experts?

 

[JohnD]

As you said, it's part of equipotential bonding. It's not main earthing of incoming services.

So it doesn't need 10mm bond to MET, just 4mm of all pipes. I can't see kitchen equipotential bonding as an electrical regulations since the
?14th?

 

[dingbat]

If you read the reg ulation you quote you should also read the definition of extraneous conductive parts in Part 2 of the regs. Read also the diagram on page 25 and understand the reasons for bonding at all.

If your c/h originates inside the house (as most domestics do) it cannot introduce an earth potential except via the incoming gas and water service pipes, which are already bonded. It's very nice of you to tie up our supplementary bonding for us though.

 

[dingbat]

As you said, it's part of equipotential bonding. It's not main earthing of incoming services.

Careful with the terms, John. This is one area where it is absolutely necessary to use the correct language.

Earthing conductor
Main equipotential bonding conductor/s
Supplementary equipotential bonding conductor/s
Circuit protective conductor
(BS 7671, p.25)

It's all the other linguistic variants that lead everybody astray and add to the confusion.

 

[JohnD]

"Supplementary equipotential bonding"

 

[Adam_151]

If your c/h originates inside the house (as most domestics do) it cannot introduce an earth potential except via the incoming gas and water service pipes, which are already bonded. It's very nice of you to tie up our supplementary bonding for us though.

What about those of us who have CH pipework buried in concrete floors ?

 

[securespark]

I can't see kitchen equipotential bonding as an electrical regulations since the
?14th?

15th.

 

[Paul Barker]

Thanks,

so because it doesn't come from outside the equipotential zone (except the gas and water which should have been Main Equipotential Bonded to the MET) it is just required to be supplementary bonded, therefore every pipe beneath the boiler should be cross bonded.

In a bathroom (which is a special location so different rules apply) the bonding is also taken to the cpc's of equipment inside the zones, but not outside.

Presumably then, as long as no zones apply the boiler pipework bonding doesn't have to go to the cpc of the dpsfs, right? Is this why when the local sparkies do the job some don't bond all the pipes (seeing as in many ways and in many places boiler pipework is already interconnected) and some don't take it to cpc or MET?

I have to tell you that when I asked this of a trainer at Napit he came back with a shrug it off response that it was not a electrical rule but a corgi rule to do boiler bonding. I am sorry, but there is no mention of it in the corgi manual which is what prompted me to get to the bottom of it, we never used to do it before the part P fiasco, then came a knee jerk reaction and loads of people are slavishly (perhaps ignorantly) bonding every pipe in 10mm and taking it to the MET. My point is, what is the point? If there is nop point, let's all go back to doing as little as is required.

By the time we have run all the other extras now required of us like condensate drain, plume management, powerflushing, most boiler swaps are running over to a second day instead of taking 4 to 6 hours like before Jags got his hands on our trade.

 

[Adam_151]

so because it doesn't come from outside the equipotential zone (except the gas and water which should have been Main Equipotential Bonded to the MET) it is just required to be supplementary bonded, therefore every pipe beneath the boiler should be cross bonded.

There is no requirement to supp bond a bioler unless it happens to be in the bathroom, or its in the airing cupboard next to the bathroom and you are actually sup bonding the bathroom at the bioler location (bathroom bonding is allowed to be just outside the bathroom and doing so makes it easier to do in a a lt of cases, but there is no rule to bond boilers in their own right, it might be argued that its a nice idea to do so, but not a rule)

In a bathroom (which is a special location so different rules apply) the bonding is also taken to the cpc's of equipment inside the zones, but not outside.

You bond everything that can introduce a potenial into the bathroom, that is all the earths of the circuits supplying kit in the bathroom zones and all metallic pipes that can introduce a potenial (which is not them all, if you have a house in plastic pipe and you stop plastic under the bathroom floor and bring 18" of copper into the bathroom then that can't introduce a potential and should not be bonded any more than a metal soap dish!) The bonding itself does not need to be in zones, it may be just outside the bathroom and an airing cupboard backing onto the bathroom is a sensible place to bond the bahroom in most cases.

Presumably then, as long as no zones apply the boiler pipework bonding doesn't have to go to the cpc of the dpsfs, right?

Unless your SFCU happens to be in a bathroom zone then there is no requirement to bond its cpc to anything

Is this why when the local sparkies do the job some don't bond all the pipes (seeing as in many ways and in many places boiler pipework is already interconnected) and some don't take it to cpc or MET?

Some are confussed about what the requirements are, some may know what they are but do things they consider are good practice but extra to the requirements

I have to tell you that when I asked this of a trainer at Napit he came back with a shrug it off response that it was not a electrical rule but a corgi rule to do boiler bonding. I am sorry, but there is no mention of it in the corgi manual which is what prompted me to get to the bottom of it,

I have to admit I thought the same, theres no electrical rule for sup bonding a boiler, and sparkies just tend to think it must be a gas rule, maybe it was a gas reg once? or maybe there are quite a few plumbers that think it is? and thats what sparkies keep getting told?

we never used to do it before the part P fiasco,

Part P doesn't say very much at all, it makes some work notifiable and it says that work has to be done in a sfae way basically (which the existing laws covering liability and duty of care to people would have covered anyway, in a more roundabout why, and would have been brought into play if you ****ed up and injured someone)

then came a knee jerk reaction and loads of people are slavishly (perhaps ignorantly) bonding every pipe in 10mm and taking it to the MET.

Bit like what I believe happened when the 15th (?) edition of the electricial regs came out, earth bonding everywhere... (we still have people sup bonding kitchens even now...)

My point is, what is the point? If there is nop point, let's all go back to doing as little as is required.

That would be sensible, also remember that bonding an isolated part doesn't increase safety, quite the opposite... so leave that sap dish alone

By the time we have run all the other extras now required of us like condensate drain, plume management, powerflushing, most boiler swaps are running over to a second day instead of taking 4 to 6 hours like before Jags got his hands on our trade.

So what has two shags done to the plubling trade, I know about something to do with part L requireing condensing boilers in most cases, but thats as far as I know is power flushing a requirement as well? and what is plume management?


If I've missed anything out or talked nonsense do to the fact that I've just got up, I'm sure someone will throw something heavy at me, but I'm pretty sure I've got everything right... will proof-read it later though...

 

[JohnD]

... I've just got up...

I spy a student

 

[Adam_151]

... I've just got up...

I spy a student

Meh, Monday and Tuesday is my 'weekend'

(work sat+sun)

 

[philrosenberg]

I can't quite remember the definition of extraneous conductive part, but I always took it to be any metal bit that sticks out of your house (please correct me if wrong) I included the overflow pipe in that so bonded it. To me it seemed quite useless, but by the letter of the regs seemed necessary.

Tell me if I was wasting my time

 

[Spark123]

An extraneous conductive part is, by definition, a conductive part which is liable introduce a potential, generally earth potential, and does not form part of the electrical installation.
These are usually items which are in contact with the generall mass of earth.
An equipotential zone is where all conductive parts are bonded together to minimise the potential difference between conductive parts in the event of a fault.
Some like to refer to this as similar to the faraday cage. If you were stood in a faraday cage and it was livened up to 240v you would not receive a shock owing to all conductive parts being at the same potential. If someone were to introduce a bare earth wire into the cage without it being connected to the cage it this would be dangerous as there is now a potential difference of 240v between the cage and the earth wire.

 

[Paul Barker]

Ah that is a great explanation that aslong as all the conductyive parts are at 240v you would be stood at 240v if you touched them and there would be a lower resistance route to ground than through you, so you probably wouldn't feel a thing. Yes I like that.

Thanks very much also to the first replier to the latest line of question from me, that was very comprehensive and answered all my questions.

I feel that there is too much boiler bonding going on. The key is to understand the intent of the regs and understand the science and apply them together, perhaps erring on safety.

I certainly shall be better equiped after this discussion to do that element of the job right but not to excess.

Two Jaggs has a website (office of the deputy prime minister) in which he basically says if you can **** through the eye of a needle you can hang a boiler. He's a lot harder man to please than corgi.