Earth Cross Bonding


Postby snanceki » Sun May 13, 2007 6:33 am

Hi.

I'm new to this forum and have found some of the advice most useful.
However there seems to be lots of confusion over cross bonding.
Maybe you can clarify.

For example:

Kitchen (No boiler).
Power socket (kettle) within reach of sink. Do hot, cold and sink need to be cross bonded. I assume so.
If so, to what earthing point.
A previous post stated it must NOT be the consumer unit unit.
Another stated to ANY earth in ANY socket.
Cable size presumably 4mm min?

What about the radiator. (3 mtrs from sink)

Boiler (not in kitchen)
Does the pipework (copper) have to be cross bonded?
Presumably so. If so to what earthing point?

Bathroom.
No electrics other than sealed halogen downlighters and pull cord.
Do all the taps, handles and radiator need to be cross bonded?
and if so to what earthing point?

Garage.
Should the gas pipe (pre or post meter) be cross bonded.

My understanding is that these "potential contact points" all need to be cross bonded (between one another) but only one location needs to be connected to earth, since all are connected by the pipework (copper) itself.

I, possibly incorrectly, have interpretted that the main earth point should be the supply box / consumer unit rather than "any socket" earth.

If so why 4.0mm cross bonding wires?

Finally what earth cable should run between the supply fuse header and the consumer unit. 4mm or 10mm min?

Appears as though the 2008 regs seek to clarify some of these points.

Any clarification would be appreciated.

Stuart
snanceki
Posts: 2
Joined: Sun May 13, 2007 6:04 am

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Postby snanceki » Sun May 13, 2007 6:46 am

Hi.

I'm new to this forum and have found some of the advice most useful.
However there seems to be lots of confusion over cross bonding.
Maybe you can clarify.

For example:

Kitchen (No boiler).
Power socket (kettle) within reach of sink. Do hot, cold and sink need to be cross bonded. I assume so.
If so, to what earthing point.
A previous post stated it must NOT be the consumer unit unit.
Another stated to ANY earth in ANY socket.
Cable size presumably 4mm min?

What about the radiator. (3 mtrs from sink)

Boiler (not in kitchen)
Does the pipework (copper) have to be cross bonded?
Presumably so. If so to what earthing point?

Bathroom.
No electrics other than sealed halogen downlighters and pull cord.
Do all the taps, handles and radiator need to be cross bonded?
and if so to what earthing point?

Garage.
Should the gas pipe (pre or post meter) be cross bonded.

My understanding is that these "potential contact points" all need to be cross bonded (between one another) but only one location needs to be connected to earth, since all are connected by the pipework (copper) itself.

I, possibly incorrectly, have interpretted that the main earth point should be the supply box / consumer unit rather than "any socket" earth.

If so why 4.0mm cross bonding wires?

Finally what earth cable should run between the supply fuse header and the consumer unit. 4mm or 10mm min?

Appears as though the 2008 regs seek to clarify some of these points.

Any clarification would be appreciated.

Stuart
snanceki
Posts: 2
Joined: Sun May 13, 2007 6:04 am


Postby sparx » Sun May 13, 2007 9:32 am

Hi there is confusion between 'Main equipotential' bonding & 'cross bonding' they are 2 totally seperate issues! so heres an attempt at clarifying,,,
Main bonding :
from service head cut out (company fuse) to consumer unit requires 16mm2.
consumer unit to your side of water stop cock & to your side of gas meter,'after flex pipe, before any branch or tee' within 600mm of meter or if extenal meter 600mm of point of entry to property in 10 mm2 .
If convenient to do so you may loop 10mm main bond from water to gas without breaking wire at first point only loop through clamp.
Cross bonding cross bonding in 4mm if unprotected from damage or 2.5mm if in mechanical protection is no longer reqd in kitchens, or bathrooms unless in bathroom there is a current using appliance ie electric towel rail when it's circuit earth must be bonded to all metal work in the room, but this can be taken fron the fused spur supplying the appliance to a convenient place ie airing cupboard where pipes are running or say in loft above. each situation varies but principle remains same,
hope this helps
As for boiler if you look most pipes to boilers go through metal 'gland plate' which the boilers mains wiring is connected to internally so no point in further earthing!
Following on from bonding regs. actually say that if electrician carries out 'high current' bond test and finds all exposed metal work that could under fault conditions come up live is effectively earthed no cross bonding reqd!!!
But still needs main bonds & nobody wants to chance it so still cross bonding more than required,
Regards SPARX
sparx
Posts: 2166
Joined: Wed Mar 21, 2007 8:33 pm
Location: The fifth continent.


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