Bonding... can I keep it at 6mm?

[Ian1981]

Wasn't having a dig at you Ian though I see it looks like it now, it was a generalisation. I always think oh God here we go The Best Practice Guide, even the title irritates me.
Me if I replace a consumer unit I will upgrade the earthing conductor and bonds because I don't like this adequate scenario because there are no parameters to judge this by.

No I agree that I would upgrade earthing conductor and protective conductors if possible as it would improve the installation to current standards.
Just I think if you can't possibly upgrade the water in this case there is an argument that it can be left as it is.
The problem with text is that you really can't tell the manner in which it's written.
No problem Westwood I like your honesty as it's to the point.

 

[joelee131]

According to the yellow book chapter 54, 543.1.1, 4mm2 is minimum with no mechanical protection, so 6mm is fine for bonding conductor.

 

[Ian1981]

According to the yellow book chapter 54, 543.1.1, 4mm2 is minimum with no mechanical protection, so 6mm is fine for bonding conductor.

That's supplementary equipotential bonding not main protective bonding conductors

 

[joelee131]

Still a bonding conductor. 6mm2 is fine.

 

[joelee131]

Make sure you check the termination to the ID plate is correct and secure.

 

[Ian1981]

Still a bonding conductor. 6mm2 is fine.

Read regulation 544.1.1
544.1.1 Except where PME conditions apply, a main protective bonding conductor shall have a cross-sectional area not less than half the cross-sectional area required for the earthing conductor of the installation and not less than 6 mm². The cross sectional area need not exceed 25 mm² if the bonding conductor is of copper or a cross-sectional area affording equivalent conductance in other metals

 

[joelee131]

544.1.1 refers to earthing conductor, the bonding to water or gas pipes is a way of reducing the risk of electric shock, that's why they are called bonding to achieve the equipotential for the whole installation wherever possible.

 

[Ian1981]

4mm would be for supplementary bonding between say hot and cold pipes in a bathroom where 4mm can be used without mechanical protection.
If mechanically protected throughout you can go as low as 2.5mm2

 

[Ian1981]

544.1.1 refers to earthing conductor, the bonding to water or gas pipes is a way of reducing the risk of electric shock, that's why they are called bonding to achieve the equipotential for the whole installation wherever possible.

No it referes to a main protective bonding conductor
Not the earthing conductor
2 different things explained in the definitions

 

[Ian1981]

No it referes to a main protective bonding conductor
Not the earthing conductor
2 different things explained in the definitions of bs 7671

 

[joelee131]

This is what the regulation say. To mechanically protect single cord bonding conduction will not be economical. so 4mm2 will be cheaper. To use 6mm2 or above is only to satisfy ones unexplained psychology.

 

[westward10]

According to the yellow book chapter 54, 543.1.1, 4mm2 is minimum with no mechanical protection, so 6mm is fine for bonding conductor.

Not sure you should be carrying out EICRs.

 

[Ian1981]

Are you yanking my crank???

 

[westward10]

This is what the regulation say. To mechanically protect single cord bonding conduction will not be economical. so 4mm2 will be cheaper. To use 6mm2 or above is only to satisfy ones unexplained psychology.

Yep you just confirmed it.

 

[joelee131]

Sorry Ian1981, mis-read your original post. You are correct the size should be 10mm2 as min. If you cannot pull new cable due to prior agreement with client not to damage any building fabric, and the exisiting cable is free from any damage including thermal, then I would put this down into the report and put C3 against it.

 

[Richard Burns]

Hi guys any advice.
I have had a request for a consumer unit change. I always carry out a condition report prior to find any issues that need resolving. The installation has a few defects but no C1's . It's a TNS installation and the main earth is 10mm and bonding to gas and water both 6mm the gas is easy to upgrade to a 10mm but the water is another matter it's virtually impossible to get a new cable to the water stop tap without causing disruption to the internal fabric. The client wants no damage! And I don't have my magic wand.
So my question is it ok to leave the 6mm to the water, continuity has been confirmed and make a note on the installstion cert?
Thanks

For your installation the minimum size for the earthing conductor might be calculated to be in the region of 5mm² and therefore the size of the main bonding would be half this subject to a minimum of 6mm². You have 6mm², so it is fine and can be left as it is is with no consideration of non compliance.

 

[Midwest]

For your installation the minimum size for the earthing conductor might be calculated to be in the region of 5mm² and therefore the size of the main bonding would be half this subject to a minimum of 6mm². You have 6mm², so it is fine and can be left as it is is with no consideration of non compliance.

Could you show your calculations Richard?

 

[Ian1981]

230/0.11 ohms = 2090 amps
2090 x 2090=4368100 x 0.1 =436810
Square root 436810=660.91/143=4.62mm2

 

[Midwest]

230/0.11 ohms = 2090 amps
2090 x 2090=4368100 x 0.1 =436810
Square root 436810=660.91/143=4.62mm2

Cheers, might start doing some of these calculation things myself.

 

[Deleted member 26818]

Hmm.
The adiabatic equation and the fact that the installation is TN-S suggest that the bonding conductors are correct and the installation Earth is oversized.
The Ze value of 0.11 ohms is very low and suggests that PME conditions apply, which would mean the bonding conductors are undersized and the installation Earth correct.
However, this is not a new installation, but an alteration to an existing one.
As such, the requirement is to ascertain whether the bonding and earthing is adequate for the protective measure intended to be used.
I imagine that ADS will be the protective mesure used, with additional RCD protection.
As neither require bonding to operate and the installation Earth complies, it would seem there is no requirement to upgrade either the earthing or bonding.