Equipotential bonding

[Notasparki]

Hi, a friend of mine has had his house partialy re-wired, by someone who i suspect is a bit of a cowboy. I am an industrial spark but used to do a bit domestics many moons ago so he has asked me for some advice. The trouble is that he has no equipotential bonding on any of his water pipes. And from where his combi is, without pulling up floor boards or doing lots of chasing into new plaster i cannot get a suitable earth path back to the main earth terminal. What i thought of doing but wasnt sure if it met with regs, wasrunning a 10mm earth cable straight down under the floor boards and sinking an earth rod directly below the boards inside the house. Is this ok to do, providing i test it out to be ok.

 

[Notasparki]

Incase you were wondering, the "electrician" he used before has disapeared!!

Typical

 

[Spark123]

No, it is the worst thing you can do.
The reason for equipotential bonding is to try and ensure everything is at about the same potential i.e. that of the MET. Doing what you suggest is the opposite of this.

 

[davy_owen_88]

The point of equipotential bonding is to ensure that all metalwork stays at roughly the same potential. If you connect the main bonding to an earth rod then it will not be at the same potential as other metalwork connected to the MET, especially during a fault which is when it is most important.

EDIT: BAH!

 

[Notasparki]

Does this mean he must start pulling boards up to go back to the CU? Or is there another way?

 

[davy_owen_88]

He could use mini-trunking or clip it at skirting height...

 

[Jolly Roger]

While on the subject, can you "overbond"?

To my knowledge the lighting / shaver socket circuit in the bathroom is not bonded. Any harm in doing so to the hot/cold water and central heating pipes?

At the end of the day, surely this will guarantee that the Earth of the circuit is at the same potential as any pipework - the whole point of bonding after all.

OK, there are cost and time implications, but is there any technical reason not to?

 

[plugwash]

jolly rodger: all circuits serving equipment need to be included in the bathroom bonding.

Notasparki: The bonding that is required by current regs in a typical domestic situation is:

Main bonding (generally needs to be 10mm) from the main earth terminal (either a seperate block or the earth bar of the CU) to incoming services (water, gas etc). How you get the wire there is up to you, conduit on the outside is often an option. So is crawling under the floor.

supplementry bonding between any circuits supplying equipment in the bathroom and any pipework liable to introduce a potential into the bathroom (that is metal or mostly metal pipework that comes into the bathroom). This isn't quite as bad as it seems because you can use circuit earth conductors and metal pipes as part of the bonding.

 

[Notasparki]

I think he has plastic pipes going into the bathroom but copper from the boiler (not sure where the copper/plastic join is) . Do the pipes from the boiler still need to be bonded even if the only exposed part in the house is just from the boiler?

 

[mikely]

It seems to be common practice to only cross bond pipes at the boiler, on the assumption that the gas and water pipes are electrically continuous from their main bonding connections, as shown in this note from Worcester Bosch

 

[Notasparki]

Thanks guys, think i know what i need to do now. Much appreciated

 

[equitum]

It seems to be common practice to only cross bond pipes at the boiler, on the assumption that the gas and water pipes are electrically continuous from their main bonding connections, as shown in this note from Worcester Bosch

It may be common practice but it is not necessary to bond at the boiler (unless the boiler is in a room adjacent the bathroom and is being done as supplementary bonding for the hot/cold/CH copper pipes in the bathroom)

 

[mikely]

The Worcester Bosch note addresses the regulation for main bonding (413-02-02) which requires that a central heating system is bonded to the MET. Is it normally assumed that the central heating system is bonded because gas and water are bonded? What would you bond if you have an oil fired boiler?

 

[equitum]

The Worcester Bosch note addresses the regulation for main bonding (413-02-02) which requires that a central heating system is bonded to the MET. Is it normally assumed that the central heating system is bonded because gas and water are bonded? What would you bond if you have an oil fired boiler?

The only items that require "main bonding" are incoming "earthy" services such as gas and water, and exposed metalic parts from other earthy elements such as structural steel, lightening protection etc. As a boiler already has its gas and water supplies bonded there is no need to cross bond at the boiler. If you had an oil fired boiler which had an earthy entry into the house and had exposed matalic parts within the house then this should also be bonded at entry to the premises. You should note that main bonding and supplemetary bonding are two different things.
Hope this helps !

 

[mikely]

The only items that require "main bonding" are incoming "earthy" services such as gas and water, and exposed metalic parts from other earthy elements such as structural steel, lightening protection etc.

So when and how would you main bond a central heating system as required by 413-02-02?