Equipotential & supplementary bonding

[Bennyboy1974]

Hi,

My folks are just about to embark on installing a new kitchen and whilst i was round there last week i noticed that the main incoming water mains (lead pipe > copper) is not earth bonded back to the consumer unit. My Dad reckons it once was but had some work done 20 years or so ago where the main was relocated and the earth has not been connected since. I would have expected to see a clamp above the stop tap and the 10mm earth wire attached, is my understanding correct??

When they had a new boiler and central heating installed some 6 years ago, i notice that all of the pipework going into the boiler has been supplementary bonded together and clamped on to the pipe, but i don't understand how this has any effect if the main service hasn't been bonded back to the Consumer unit??

It may well be that i have no idea what i am talking about and everything is fine, however, something doesnt look right to me and i wanted to check. If they install a metal sink, will this need to be bonded to the pipework so that it all ends up back at the CU?

Look forward to your replies.

Cheers

Ben

 

[Richard Burns]

Metallic incoming services, gas. oil, water in general will probably require bonding back to the Main earth terminal (MET); normally either a block of metal connectors near the incoming power supply or the earth bar of the consumer unit.
If the central heating pipework is fully correctly supplementary bonded then that area would not be subject to dangerous voltages during a fault.
If the incoming gas/oil is bonded back to the MET then this will connect to the water pipes to some extent via the supplementary bonding and limit the risk.
There are reasons why a main service may not need to be bonded, but this is normally for plastic incomers.
The size of the bonding conductor does vary according to the installation but 10mm² is generally suitable for most average single domestic properties.
The location of the bonding is usually close to the incoming stop tap but may be further away if access is limited.

 

[Bennyboy1974]

Metallic incoming services, gas. oil, water in general will probably require bonding back to the Main earth terminal (MET); normally either a block of metal connectors near the incoming power supply or the earth bar of the consumer unit.
If the central heating pipework is fully correctly supplementary bonded then that area would not be subject to dangerous voltages during a fault.
If the incoming gas/oil is bonded back to the MET then this will connect to the water pipes to some extent via the supplementary bonding and limit the risk.
There are reasons why a main service may not need to be bonded, but this is normally for plastic incomers.
The size of the bonding conductor does vary according to the installation but 10mm² is generally suitable for most average single domestic properties.
The location of the bonding is usually close to the incoming stop tap but may be further away if access is limited.

Cheers for the detailed answer, thats great. If all of the central heating pipework has been bonded together but the main has not been bonded to the Earth bar at the Consumer unit then is it a pointless exercise? Apologies if my terminology is wrong, but i have been googling as much as i can to try and understand but i reckon there is some fundamental bit of info that i am just not understanding. I think my dad is going to call in an electrician anyway now as he is thinking of upgrading the old fuseboard to a new consumer unit. Thank you.

 

[Richard Burns]

Probably easiest to get an electrician as they can assess on site.
I cannot describe bonding simply on a forum so I will attach the following images from the wiring regulations guidance notes.