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.