What size earth for boiler

[Mick Leek]

Hi All

just a quick one, what size earth bonding should run from new boiler installed in new extension to consumer unit ?

I have been told 10mm ? seems a lot

Cheers guys

Mick

 

[Adam_151]

No reason to main bond a boiler at all, but 10mm is the norm for main bonding

 

[RF Lighting]

No reason to main bond a boiler at all

Except for the regulations of course
BS7671 Regulation 413-02-02 section (iv) to be precise

Please check you information is correct before advising it

 

[Crystal]

There is no reference to boilers in my copy of BS7671 Regulation 413-02-02 section (iv).

 

[RF Lighting]

BS7671 Regulation 413-02-02 section (iv)
Requires "main equipotential bonding bonding conductors complying with section 547 [10mm2 minimum copper equivalent cross-sectional area of the main equipotential bonding conductor for copper equivalent cross-sectional area of the supply neutral conductor 35mm2 or less] shall connect to the main earthing terminal for that installation's extraneous-conductive-parts including the following:" "(iv) central heating and air conditioning systems"
Surely this is a boiler is it not?
What does your regulation 413-02-02 refer to?

 

[Adam_151]

I was being a little generic there, it only applies to extraneous-conductive-parts, its not going to apply to the boiler* (well i'm having trouble dreaming up a situation where it would), I suppose there is a slim chance that a central heating pipe or two might need bonding (if they leave the equipotential zone to go to a garage or outbuilding, etc)

*the reg mentions CH systems generally, not boilers specifially

413-02-02 doesn't mean you go around bonding everything that could sometimes qualify as an ECP even though if it isn't, or you can get into some weird situations, if you blindly bonded aircon systems whether or not they had ECPs, are you going bond the fridge? pretty much the same thing inside them as an aircon system...

EDIT: spelling

 

[RF Lighting]

Is it not good practice to main bond and cross bond a boiler so that the very remote chance of any pipe work becoming live is removed? I know I would prefer this situation (belt and braces), but I have to admit my bonding in my own home is sadly lacking . In reply to the OP IMHO 10mm2 is the correct size to use. Feel free to shoot me down in flames if you feel this is incorrect. This argument could go on forever.....I really need to go to bed now.

 

[TeesdaleSpark]

Regulation 413-02-02 states "main equipotential bonding ... shall connect to the main earthing terminal extraneous-conductive-parts ... including ... (iv) central heating and air conditioning system"

So if a domestic central heating systems is an extraneeous-conductive-part then there is no alternative than to bond. The only question is: is the heating system an extraneous-conductive-part or an exposed-conductive-part?

BS7671 defines these:
Extraneous-conductive-part. A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation.

Exposed-conductive-part. A conductive part of equipment which can be touched and which is not a live part but may become live under fault conditions.

The pump and part of the boiler must be an exposed-conductive-part. But where does the exposed part stop and the extraneous part start/stop if at all. To my mind the boiler is an exposed part and is protected by a cpc. In my opinion to say the pipes and radiators are exposed parts would be stretching the definition.

The radiators and pipe work are not forming part of the electrical installation, are conductive (unless plastic pipes are used) and are liable to introduce an earth potential because they are connected to equipment that is earthed i.e. boiler, supplementary bonding and possibly a water pipe. Therefore I consider them an extraneous-conductive-part. If it's an extraneous part there is no choice but to provide bonding.

However 543-02-06 allows the use of extraneous-conductive-parts as a protective conductor as long as it satisfies some requirements. These requirements are generally met by the connection of copper gas and/or water pipes to the boiler.

So in summary, generally you would need to provide main equipotential bonding to the central heating system but this may be achieved by the fact the water or gas pipe is already bonded.

 

[Mick Leek]

Cheers adam, and the rest of you..

Sorry i didnt want to start a debate.

Maybe i should clarify a few things,

Firstly, its a new extension and re location of a a new boiler, Used to have an old back boiler in a different part of the house) secondly my main consumer unit hasnt any spare outlets so having to install a MINI unit for new plug ring and lighting.

I have purchassed a garage type consumer that the shop said would be fine. Its only a single storey extension ( living room & Utilty)

And thirdly, the original earth bond apears to only run to the bathroom ? I havent seen any additional main earth wires whilest all the floor boards were up ..

Thanks

Mick.