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Is this method of earthing a water pipe permissible?

Arran Cameron

A house has the main earth terminal block located next to the electricity supply cable in a cupboard in the living room. The water supply is a blue MDPE pipe located in the kitchen that transitions to a copper pipe about 2m before the stop tap.

About 1m away from the earth terminal block are a pair of copper central heating flow and return pipes. These same two pipes are located right next to the copper water supply pipe in the kitchen.

The easiest, and most economical on cable, method to earth the pipes is to connect the earth terminal block to the central heating pipes in the living room, then connect the central heating pipes to the water supply pipe in the kitchen.

Is this permissible, or must a long length of earth cable be installed under the floorboards connecting the earth terminal block to the water supply pipe?

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    You need a surprisingly short insulating section to limit any currents to a level that is negligible (less than 10mA say) The rules for UK drinking water purity means that a foot or two of water  filled 15mm dia plastic pipe is  likely to be many 10s of k ohms if not exceeding 100k. Gas and oil are essentially insulators, It gets more complex with contaminated water, perhaps central heating systems, and swimming pool circulators, but  these do not commonly pass out of the building under terra-firma and back in again. If a metal pipe comes in and changes to plastic - the opposite of the case here I think, then it is sometimes just easier to box in or cover the short section so it cannot be touched.

    Mike.

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    You need a surprisingly short insulating section to limit any currents to a level that is negligible (less than 10mA say) The rules for UK drinking water purity means that a foot or two of water  filled 15mm dia plastic pipe is  likely to be many 10s of k ohms if not exceeding 100k. Gas and oil are essentially insulators, It gets more complex with contaminated water, perhaps central heating systems, and swimming pool circulators, but  these do not commonly pass out of the building under terra-firma and back in again. If a metal pipe comes in and changes to plastic - the opposite of the case here I think, then it is sometimes just easier to box in or cover the short section so it cannot be touched.

    Mike.

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