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

 

[Bobster]

What do you think, and what do the regs say on the matter?

 

[crotley32]

Don't have the regs to hand at the moment my friend I'm actually on holiday and forgot to bring it with me.
It's just a question I've been pondering over.
I personally think 6mm is fine. I was just wanting a few others input.

 

[Bobster]

What's the Ze?

Should point you in the right direction of looking for an answer.

 

[crotley32]

0.11 ohms relativley low

 

[The Ghost]

Adiabatic equation?

 

[Midwest]

Never used the adiabatic equation to calculate size of the EC myself, too lazy is my excuse (more likely clueless ). I prefer to use Table 54.7.

I guess the adiabatic equation, could possibly calculate that the 10mm EC may be of sufficient size , but I always thought the protective bonding conductors were selected (reg 544.1.1) rather than calculated?

Perhaps someone could demonstrate some examples of the adiabatic, for us lessor mortals (or lazy arses!), if the OP supplies some more detail.

 

[Ian1981]

In a TN-S the bonding conductors must not be less than half the size of the earthing conductor and not less than 6 mm.
If the existing bonding conductors show no signs of thermal damage, have continuity and are in good order they could be left as they are.
Sure others will disagree but if they've been installed for quite a number of years then there is no problem.
You wouldn't even code them on a eicr if no problems where found.
Adiabatic equation is for sizing protective conductors only and not equipotentioal protective bonding conductors.
Adiabatic is I2t square root divided by 115 if conductor is Incorperated in a cable or divided by 143 if seperate and not bunched.

 

[Midwest]

I seem to recall, the idea of leaving undersized EC's & protective bonding conductors, as is, if there's no sign of thermal damage is no longer passé, I might be wrong.

 

[Ian1981]

I seem to recall, the idea of leaving undersized EC's & protective bonding conductors, as is, if there's no sign of thermal damage is no longer passé, I might be wrong.

Non-compliances with the current editon of BS 7671 that do not give rise to danger and do not require reporting

• Inadequate CSA of main protective bonding conductors provided that the conductor is at least 6 mm2 and that there is no evidence of thermal damage
  
  Taken from electrical safety first best practice guide updated to amendment 3

 

[Midwest]

If you forgive me, I will retort in due course and quote my citation (might be about PME?), but her indoors is demanding I make the tea!

 

[Ian1981]

Using the Adiabatic equation I get a required CSA of 5 mm2 that is assuming t in the equation is 0.1 seconds.
So 10mm will satisfy the equation for the CSA of the earthing conductor

 

[westward10]

Non-compliances with the current editon of BS 7671 that do not give rise to danger and do not require reporting

• Inadequate CSA of main protective bonding conductors provided that the conductor is at least 6 mm2 and that there is no evidence of thermal damage
  
  Taken from electrical safety first best practice guide updated to amendment 3

Aha The Best Practice Guide, it is a fool who relies upon this as opposed to BS7671.

 

[Midwest]

Whilst my Pigeon with warm foie gras sorbet, are resting, I've looked back at my recollections, and the advice given by our cohorts, Certsure, was for PME main protective conductors.

However, it does refer to reg 132.16, 'the earthing & bonding, shall be adequate' and makes no mention of existing installation.

 

[Midwest]

Perhaps Electrical Safety First, and its forbearers Certsure, should have a little chat?

 

[Midwest]

Back to my chilli, urrrgh I mean me Pigeon

 

[westward10]

I wonder how one defines "adequate".

 

[Ian1981]

Aha The Best Practice Guide, it is a fool who relies upon this as opposed to BS7671.

I'll grab my jesters hat then shall I!?

What a good persuasive answer that was!

 

[Ian1981]

I wonder how one defines "adequate".

Sufficient, acceptable, enough, ample

 

[westward10]

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.

 

[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.

 

[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.