Bonding 😣

bennie · Apr 30, 2024

No waffling, going to get straight to the point. Main water on the exterior of the building in plastic. Changes to copper inside the building. According to regs doesn't need main bonding. Incomer to building is 120mm SWA, TNS with a 70mm earth. Current bonding to the water is 10mm but as said according to the regs it's not needed. Many water heaters & showers on the installation so when an insulation resistance test was carried out between the MET & the stop cock it was showing a dead short. As main bonding isn't required but there is still resistance between the pipework & the MET should there just be supplementary bonding & if so does that mean 6mm would be sufficient.

westward10 · May 1, 2024

In general terms the earthing system is not relevant regarding supplementary bonding.

bennie · May 1, 2024

westward10 said:
In general terms the earthing system is not relevant regarding supplementary bonding.

Disregard the supplementary bonding question. If services are insulated from earth but still have a main bond in a TNCS system & have accessories that give a pathway surely that would be an issue & would need noting.

Pretty Mouth · May 1, 2024

bennie said:
Disregard the supplementary bonding question. If services are insulated from earth but still have a main bond in a TNCS system & have accessories that give a pathway surely that would be an issue & would need noting.

Not quite following you. Is your concern diverted neutral currents, or is it open supply neutral causing a rise in voltage on the earthing system?

bennie · May 2, 2024

Pretty Mouth said:
Not quite following you. Is your concern diverted neutral currents, or is it open supply neutral causing a rise in voltage on the earthing system?

Open supply neutral

Pretty Mouth · May 2, 2024

bennie said:
Open supply neutral

Any metalwork connected to the MET could rise in voltage compared to true earth under an open supply neutral fault (on TN-C-S), and that would include the bonded pipework. However, in the property you're inspecting, the pipework is connected to the MET in numerous places, so removing the main bond isn't going to make a real difference.

Either way, the regulations permit the general use of TN-C-S, so it wouldn't be something you would code on an inspection. There are circumstances where TN-C-S is not permitted (eg caravan hookups) in which case you would code it