equipotential bonding request

29 Jun 2008
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West Midlands
United Kingdom

Having done an EICR today, i inspected and saw that there was, off an external MET, a 10 mm main earthing conductor to a tnc-s supply to also, the cu Met (as plit load 2002 crabtree) from this, 10mm2 to nearby gas and then 2x 4mm2 sheathed earths to the water.

Testing revealed. 0.03 ohms from water pipe to MET end, with other eathing bonding conductors out off circuit.


I know all PME supplies require 10mm2 equipotential bonding, but does the reading above allow me to preclude this, other than the main earth and other items noted

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With my mpfc does allow it, but PME demands the calculation is taken away from you with 544.1.1

Now the asterix at the bottom of the page 134 quotes that the equivalent material affording equivalent conductance.

Well its 0.03 ohms, can i agree with my opinion, i need some guidance.
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sorry rob, i meant PFC or mpfc (maximumpfc at cu)

anyway, the adiabatic is not inportant, i was saying that the adiabatic satifies the existing main earthing conductor but i was interested in the Equipotential bonding or, Main protective bonding, if you will, lol
The 10mm2 minimum requirement is just that and not related to anything other than the current carrying capacity of the conductor.
In theory the supply could be issued with an improvement notice by DNO staff or even disconnected on safety/non compliance grounds (see ESCQR).

In reality either is unlikely but there is not a way around it
I would say that the current installation is code 2.

You can not have a MPB smaller than 10.0mm² on a PME supply. That bonding isn't sized purely for fault clearing. Think about network currents, and even a failed CNE conductor where the extraneous parts are connected back to the the CNE somewhere else on the network. The bonding is going to have to carry the entire installation current for sustained lengths of time.

What the asterisk is saying is that you could for example use the steel structure of a building as your bonding conductor providing it has at least the same conductance as the required copper bond. So for example if the regs require you to bond an incomming service with a 10.0mm² copper bond, then you need to ensure your steel bond is ~90mm²* as copper is much more conductive than steel.

It isn't saying that you can use what ever size cable you like as long as it's resistance is less than 0.05Ω

* that's a guess without actually working it out
IIRC the NICEIC advise that an undersized bond is C3 unless there is signs of thermal damage apparent. though I'd probably lean to C2 as well though.
so, theoretically, i could have a piece of balsall wood as a main protective bonding conductor as long as it was <10mm2 cross sectional area and was less than .005 ohms reistancance.
No. There is a specific list of what may be used as a main protective bonding conductor, and the precautions that must be taken to ensure against their removal etc. in the regs.
so, theoretically, i could have a piece of balsall wood as a main protective bonding conductor as long as it was <10mm2 cross sectional area and was less than .005 ohms reistancance.

No. Any alternative material used as a MPB must be on the approved list and be of copper equivalence with regard to conductance.

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