I was in hosue last week. The Spark said all you need do to bond is for the upstairs, take an earth wire from the meter to the bathroom light earth terminal then the switch, then the pipes under bath taps, jump from one to the other, then to the basin taps, as per bath and then to radiator copper tails and stop.
For downstairs, an earth wire from the meter to the pipes of the boiler in the kitchen, just linking each boiler pipe under the boiler an then stop. None on the sink taps, pipe under the sink or to the ligh fittings or switch.
Then from the meter earth block to the gas pipe at the meter and the water pipe as it comes into the house.
Not quite, he seems to have lost the plot somewhere along the way.
With bathrooms you are simply attempting to create an supplementary equipotential zone. This involves connecting together all exposed metalwork that has the capability of introducing a potential into the zone. So basically metal pipes (supply or waste), any exposed building metalwork (unlikely in a domestic place), and the CPCs of any circuits supplying the room (which would include potentially ring or radial circuits feeding appliances, and shower feeds etc). Where appliances are present you may make use of the CPC supplying it as a bonding conductor. There is *no* requirement for a dedicated connection to the main earth terminal.
Kitchens do not actually need supplementary equipotential bonding at all since they are not "special locations".
Both of the above are separate from the requirements to provide main equipotential bonds between incoming services. The main bonding should include the CH system, which may or may not be in the kitchen. The required cable sizes are different from those used for supplementary bonding as well.
Maybe there are different regs in this mysterious place Hosue...
What I've just done is to apply main bonding between elec meter/gas meter/rising main (the latter not being in the kitchen); then separately in the kitchen applied supplementary bonding between kitchen sink/taps and the gas pipe, CH flow and return at the adjacent boiler.
I appreciate that kitchen supplementary bonding isn't a requirement (but the sparks who does my testing insists on it so I just don't argue!) but does my scheme 'work' OK in terms of the CH system?
Connection from the main earth terminal in 10mm^2 yellow/green single to the main incoming services and any "extraneous conductive parts".
BS7671 spells it out as:
413-02-02 In each installation main equipotential bonding conductors complying with Section 547 shall connect to the main earthing terminal extraneous-conductive-parts of that installation including the following:
(i) water service pipes (ii) gas installation pipes (iii) other service pipes and ducting (iv) central heating and air conditioning systems (v) exposed metallic structural parts of the building (vi) the lightning protective system. Where an installation serves more than one building the above requirement shall be applied to each building.
547-02 Main equipotential bonding conductors
547-02-01 Except where PME conditions apply, a main equipotential bonding conductor shall have a cross-sectional area not less than half the cross-sectional area required for the earthing conductor of the installation and not less than 6 mm2. The cross-sectional area need not exceed 25 mm2 if the bonding conductor is of copper or a cross-sectional area affording equivalent conductance in other metals. Where PME conditions apply, the main equipotential bonding conductor shall be selected in accordance with the neutral conductor of the supply and Table 54H.
(and 54H says 10mm for a supply neutral of 35mm^2 or less.)
Hmm, thanks, hadn't realised that one. OK, so if my spark's feeling particulary anal, then to connect the boiler to electric meter would require a new 10mm^2 earth cable right through the house (which would necessitate a lot of destruction of freshly plastered surfaces - not great.)
Would it be allowable to run a short (new) cable from the exisiting earthing clamp on the rising main as far as the nearest CH pipes (which is a long way from the boiler; and would the earth route from the CH back to the electric incomer would be via a non-continous cable)?
Might be worth asking him. Since the extraneous conductive paths in this case have no "entry point" into the property, one could argue that there is no requirement to make the connection at the boiler. (other than that being a place where you can be reasonably assured the pipes will go)
I believe it should be unbroken[1], but I am not sure if that is actually a hard requirement. There is no reason that the conductor has to pass round the inside of the house either. You may well find that the presence of supplementary bonding on the boiler connections (even if not actually required), may satisfy an inspection. The primary thing that one would be looking for is a connection to the water and gas mains in most cases.
[1] The on site guide makes reference to "unbroken" conductors looped through the clamps, but I can't immediately see an equivalent clause in BS7671
I don't believe there is one. However C&G specify it as a fault for visual identification in one of the practical tests for the 2391 Inspection, Test and Certification course. A bit of "Gold Plating" has gone on I think.
It's important to realise that the items in that list only have to be main-bonded if they come within the definition of extraneous-conductive-parts - i.e. if they are liable to import a potential from outside the equipotential zone. A typical gas CH system with all its pipework above ground level and not in a steel-framed building will not usually require bonding. An oil-fired system with the fuel feed pipe entering from underground should be bonded though.
Oops, I meant 528-02-04. Incidentally, cable-tying bonding conductors along gas and water pipes to keep them tidy is a deprecated practice, at least according to NICEIC, by dint of the same regulation. Wiring should not rely on the presence of any other service hardware for its support.
That was almost a Rimmer Vs Kryten moment (for Red Dwarf fans!) ;-)
That seems like a pretty tenuous link.... in so far as you could remove a bonding clamp from a pipe without disconnecting its (potentially not unbroken) wires. I take it there is a note in one of the "guidance to the regs" type docs?
That at least seems like a more logical deduction from the above regulation.
I think the idea is that a plumber (for example) can completely remove a redundant clamp without affecting anything downstream and without the need to re-make an electrical connection.
Pass - I don't have a full up-to-date set. I can't see any reference to it as an inspection point in the current version of GN3, nor in an old edition of GN1. It might be in the new GN8 on earthing and bonding, but I'm waiting for the 17th edition version to appear before I buy that one.
See also the article on earthing and bonding in /Wiring Matters/ Issue
Gas boilers in kitchens I see all the pipes under bonded and in some, and not in others, the earth cable run back to the meter. Other boilers I see not bonded at all.
It appears that this bonding is so confusing that Sparks just bond everything in sight and run it back to the meter to be sure.
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