Protective bonding conductors in a flat?

alanl · Dec 2, 2011

I've just been to a flat tonight to look at some potential work, but there is no bonding conductor to the incoming water pipe inside the flat.
I had a quick look in the main distribution board cupboard of the flats, but could see no evidence of bonding to the water, and the main water incomer to the flats is hidden away anyway.
So, should there be protective bonding to the water in each flat?
Or, is one bond enough between the main block of flats Dist. Board and the water incomer for the flats?
I'm presuming not, and it will need some 10mm put in, but would like others thoughts on this.

Thanks
Alan.

Guest123 · Feb 2, 2012

Main protective bonding is carried out to extraneous conductive parts. The definition of an extraneous conductive part is "a conductive part liable to introduce a potential, generally earth potential and not forming part of the electrical installation".

Therefore as you've said it is to protect against fault currents introduced to the installation from a source external to it.

1shortcircuit · Feb 8, 2012

I'm pleased that the forum search function works correctly and I found this thread :thumbsup

Does someone have the exact wording from GN8 regarding this issue that they don't mind posting on here pleeeease

(going to search google in a moment)

I'm interested to see this because it will help me resolve a situation that I am in the progress of quoting on (4 flats, only one with gas bonding, 4 separate meters all sharing water bonding and one main earth rod)

I quoted to bond from top flat to within 600mm of the outside gas meter but then the client asked, IF I was to do all four flats could it be done from the main earth terminal to each meter. Thinking along the same lines as Spin I couldn't see an issue with this but it seems I need to look into this further.

Also, surely if each flat is classed as it's own installation then it should also be supplied with it's own seperate means of earthing (rod in the case?)

With regards to the bonding to the gas in each flat would I presume that the bond would be taken from the main earth terminal in the CU to within 600mm of the POINT OF ENTRY to that flat and THEN a main bond from the MAIN earth terminal in the meter cupboard (basement) to within 600mm of each meter (one continuos bond as all next to each other)

Sorry OP for adding this but I believe this is relevant to your post and doesn't warrant creating another thread discussing the same issue

Kind Regards

1SC

Engineer54 · Feb 8, 2012

You bond from each apartments CU position MET/MET to the water/gas service as it enters that apartments boundaries. Doesn't matter if the main earthing system is TT or TN.

As for a TT system earth supplying this multi dwelling building, no, each apartment wouldn't need it's own rod as you put it. But it would be a good idea not to rely on a single 1m rod!! Personally i'd use your one rod per apartment on installing a 2 position TT system each with 2 coupled rods. At the very least this will give you a stable system that's not prone to failure during adverse weather conditions. ...And depending on soil conditions, certainly give you a better/lower Ra value overall, for these 4 apartments...

spark 68 · Feb 8, 2012

@ 1shortcircuit:
Re:GN8 (5.7 p52/p53) the relevant part/s

Multi-occupancy premises:

BS7671 requires main equipotential bonding in each installation.

(definition of installation and origin given here)

It is clear that BS7671 requires main equipotential bonding in each and every installation connecting together extraneous conductive parts to the MET and this would apply equally to seperate installations on a multi occupancy building.

This then goes into details on minimum size CSA for PME etc....

1shortcircuit · Feb 8, 2012

Engineer54 said:
You bond from each apartments CU position MET/MET to the water/gas service as it enters that apartments boundaries. Doesn't matter if the main earthing system is TT or TN.

As for a TT system earth supplying this multi dwelling building, no, each apartment wouldn't need it's own rod as you put it. But it would be a good idea not to rely on a single 1m rod!! Personally i'd use your one rod per apartment on installing a 2 position TT system each with 2 coupled rods. At the very least this will give you a stable system that's not prone to failure during adverse weather conditions. ...And depending on soil conditions, certainly give you a better/lower Ra value overall, for these 4 apartments...