Special Locations Pool Rebar Bonding

Question

Hi all, in a domestic pool installation, the contractor has formed the concrete base of a swimming pool, linked to the main house, and not bonded the slab rebar. My understanding is that the contractor will now need to expose the rebar and bond back to the main earth terminal. My concern is this will affect the integrity of the pool slab (future weak spots and leaking) and also whilst trying to achieve complete rebar continuity could result in many holes. I believe there is insulation and screed going on top of the slab (I maybe wrong), could a secondary earth nest be sat on top of the slab or would this create more issues by in essence adding secondary extraneous conductive parts?

Sparkingchip · Accepted Answer

This needs to be considered along with your installation earthing question. 
 engx.theiet.org/.../domestic-2-phase-system-and-additional-single-phase-supply

mapj1 · Answer

you wont need complete re-bar continuity, just two widely spaced points of connection that you can do a ring-round meter test to. The steel to steel contact does not need to be great, after all the resistance of the concrete is in series between it and terra-firma, and the same concrete envelopes all the rebar thus linking any poor twizzle wire contact. Actually, unless the rebar is folded up the sides in a way that means accessing it is easy, beating holes in a swimming bath is a really bad idea.... Can you get away from PME earthing and the need to earth the rebar altogether ? Mike.

AJJewsbury · Answer

I'm probably being dim ... but where has this requirement for bonding rebar come from? Unlike 705 I can't see any particular reference to rebar in 702. There is a reference to an earth mat or electrode providing a resistance of 20 Ohms or less when using PME, but there doesn't seem to be any guarantee that the rebar would achieve that (if there's a plastic sheet under the slab, it's probably quite unlikely). Is the assumption that the rebar is an extraneous-conductive-part? If it's not accessible from within the installation (either directly or via something conductive, e.g. damp concrete) is that the case here? 
 - Andy.

gkenyon · Answer

AJJewsbury said: There is a reference to an earth mat or electrode providing a resistance of 20 Ohms or less when using PME, but there doesn't seem to be any guarantee that the rebar would achieve that (if there's a plastic sheet under the slab, it's probably quite unlikely). 
 See also G12/5. It's also commonly done for ground floor shower blocks in sports clubs etc ... and cattle sheds. 
 No "firm requirement", but if there is a grid it should be bonded. 
 There is no guarantee that such a grid will prevent "tingles" from diverted neutral currents - it depends on the magnitude in the area. A TT approach might be recommended where this is practicable (e.g. suitably separated outbuilding).

Special Locations Pool Rebar Bonding

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