Bonding again

[Plonker 3]

Went to look at a job the other day where the water and gas were correctly bonded in the house. But they also had a outhouse which was connected to the house via a covered walkway.

Inside there was a 2 way RCD board fedding a light and several sockets in the outhouse.

There was also a incoming water pipe from the house which came from under the floor. Would this also need bonding too or because it is bonded on the house is that satisfactory?

 

[telectrix]

i would bond it. 1. the bond in the house could fail. 2. plastic could be fitted between house and garage.

 

[malcolmsanford]

That is a good one and here we go.

If you've extended the equipotential zone to the outhouse and that is bonded, and you take a water feed to the outhouse from the bonded equipotential zone, then theoretically there should not be any PD, and as a outhose in the BS 7671 is not classed as a special location when regarding bonding, then I would say no need to bond, especially as you have RCD protection.

But as Tel says there are several imponderables, and the main one for me would be continuity of that water pipe with the bonding.

 

[Plonker 3]

I did carry out a quick contiuity test between the earth bar in the RCD board and the water pipe and it was 0.63 ohms.

I was only carrying out a replacement of a batten lamp holder so I don't have to bond it for that do I? I told the customer I would write up a quick report for her to inform her of my findings and told her that should any installation work be carried out in the out house it would need bonding then.

 

[malcolmsanford]

Personally I would have done a continuity test from pipe to MET and then an IR from pipe to MET just to see what I had.

Again because of the RCD protection I would not worry about just the changing of a batten holder. I would though have tested the RCD with all 7 tests, I assume it is a 30mA kind

Finally before you put things in writing to a customer make sure what your writing is correct. Don't go advising them that if future work is carried out, you HAVE to bond that pipe, when you may not have to. Bonding something that does not need bonding, is just as dangerous as not bonding something that does

 

[Plonker 3]

Again because of the RCD protection I would not worry about just the changing of a batten holder. I would though have tested the RCD with all 7 tests, I assume it is a 30mA kind

Yes it was 30ma and I carried out the relevant tests and filled out the results on a MWC.

Finally before you put things in writing to a customer make sure what your writing is correct. Don't go advising them that if future work is carried out, you HAVE to bond that pipe, when you may not have to. Bonding something that does not need bonding, is just as dangerous as not bonding something that does

I know that, was just looking for some clarity on the situation, so I should say it would need testing to the current BS7671 standards at the time, and may need bonding if it doesn't meet these standards, don't really want to confuse the customer too much or try and frighten them into thinking their house is unsafe.

Does anyone have a PDF of a leaflet I could give to the customer explaining bonding?

 

[malcolmsanford]

Take the scenario on, you have water service coming into the house that is bonded as per the 17th. The house is all copper and there is an outside tap fed from a spur from the kitchen sink.

Now because you have bonded the services coming into the house the whole house in now an equipotential zone with no potential difference.

Next to the tap say 4ft away you have a socket again spurred from the kitchen RFC, so your pipe and socket are extensions from the equipotential and therefore bonded and are of the same potential .................but your now in the garden and of course that is of a different potential and so what is the best solution

 

[Deleted member 9648]

Take the scenario on, you have water service coming into the house that is bonded as per the 17th. The house is all copper and there is an outside tap fed from a spur from the kitchen sink.

Now because you have bonded the services coming into the house the whole house in now an equipotential zone with no potential difference.

Next to the tap say 4ft away you have a socket again spurred from the kitchen RFC, so your pipe and socket are extensions from the equipotential and therefore bonded and are of the same potential .................but your now in the garden and of course that is of a different potential and so what is the best solution

If you are in the garden you are completely surrounded by earth potentials,you cant create an equipotential zone,no point in bonding anything.

 

[Plonker 3]

Right, so it should be bonded in the future, due to it being buried underground and introducing a different potential to the outhouse?

 

[malcolmsanford]

Right, so it should be bonded in the future, due to it being buried underground and introducing a different potential to the outhouse?

Then there is a chance because of it being buried and you've extended your equipotential zone from the house into the outhouse then yes it would most likely be at a different potential and need bonding, but you would need to bring it back into the equipotentiall zone by bonding back at MET.

What I was thinking on your OP was a pipe not buried but say run around a wall. I know you said under the floor, but until actually said buried.

 

[Plonker 3]

Sorry, yes it is run under concrete should have made that clearer really :banghead: