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

[crotley32]

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

 

[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.

 

[mickfred]

Or you could disconnect and measure it and see it's resistance

 

[hightower]

Regs are very clear on this, as Richard has already eluded to: TNS with a min earth of 5mm (as OP has calculated), bonding is half that to a min of 6mm. I wouldn't even install 10mm for the 'easy' gas, 6mm is fine and perfectly within the standard.