Earth Bonding on New Consumer Unit

[DropDeadFred]

I have been told that when upgrading my old style fuse box with a new consumer unit it needs to be double earth bonded. The existing box has an earth bond running to a gas pipe 30cm away but this is the only metal pipe nearby. My water mains pipe runs under the house and emerges over 20ft away from the location of the fuse box.

Is this correct and if so, what are the options to meet the regulations?

PS This is not a job I will be going anywhere near myself but just wanted to make sure I knew what I was letting myself in for if floors had to come up (concrete!!).

Cheers

 

[didthathurt]

Not quite.
The new consumer unit will need an earth connection to it. The water pipe used to be allowed to be used for this purpose, but not anymore. Both the water and the gas pipes will need to be connected to the earth either within 600mm of your side of the meter or where the pipe enters the building if the meter is outside.

How this is done depends on what you have now, and what is available. What sort of house in what sort of location do you have?

 

[DropDeadFred]

I have a Semi detached corner plot property elevated 4ft from street level. As such the water main runs from the street, under the concrete floors, only emerging in the kitchen at the back of the property. Should I expect to see an earth wire on this mains pipe after it enters the kitchen?

The fuse box has one earth running back to the supply companys earth near to the main fuse and another one connected to the gas pipe nearby. (Both at front of property inside the hallway)

If a second bonded earth is still necessary in this situation, what else can they use without digging up the floor as there are no other supply pipes nearby (other than next doors!!)

Hope that makes sense

 

[JohnD]

You can run it to the water pipe where it emerges inside your property. Sounds like it rises through the kitchen floor. Bond on your side of the stop cock which I hope is a few inches above.You will be using a 10mm G&Y which is fairly big. It must have no joints in it between the CU and the pipe.

If you are thinking of having a new CU, it can be useful to fit an earth Block as an MET (at least 4-way but 8 can be handy) next to the service head and meter. This is because many older CUs do not have have enough room for the 16mm from the service head, plus the 10mm from the gas and the 10mm from the water.

Leave some slack in the earth wires so they will go into the new CU when fitted. Each Earth Bonding connection and the MET must have a permanent label saying Electrical Earth Do Not Remove (one is provided with each bonding clamp).

 

[DropDeadFred]

Silly Question John...but where are they allowed to run the earth cable back from the kitchen to the CU? Can it go behind skirting/under carpet etc. The flooring is concrete and don't fancy ripping my floor up.

 

[dingbat]

Please, please, please get the terminology right!

You have only one Earthing Conductor, between the MET (whether internal or separate from the CU) and the means of earthing.
Then you have as many Main Equipotential Bonding Conductors as you have 'earthy' services entering the equipotential zone, each connecting that service to the MET, which should be labelled "Safety Electrical Connection - Do Not Remove" (shame on you, JohnD!)

There is no such thing as 'earth bonding', earthing and bonding are different things and the mixing of terms is part of the reason a lot of supposedly qualified sparks, never mind Joe Public, have no idea what the green-and-yellow cables are actually for.

Phew, that's better. Had to get that off my chest!

 

[DropDeadFred]

I'm not qualified in any way to know all the terminology, but I'm sure you have got the drift?

""Then you have as many Main Equipotential Bonding Conductors as you have 'earthy' services entering the equipotential zone, each connecting that service to the MET""

So going back to my original question, bearing in mind the location of the services entering the building, are they classed as in the equipotential zone?

 

[JohnD]

I get the impression you are hoping someone will tell you not to bother bonding the incoming watermain.

No chance

 

[Steve]

The equipotential zone is YOUR WHOLE HOUSE. All metallic services rising out of the ground and/or entering the house must be bonded.

Have you thought about running the bonding conductor in the ceiling? Or find the boxing that carries the water pipes upstairs and run in that back to the point of emergence. In our house, said boxing runs along the kitchen ceiling, right past the back of the consumer unit, very convenient

There's normally a void under and behind kitchen cabinets that is ideal for running cables in too.