EICR - Undersized earthing conductor

[Andy78]

Doing inspections today and found a couple of properties with under sized earthing and bonding conductors. Earthing system is TNC-S and features 6mm earthing conductor and 6mm bonding conductors.
I normally code 6mm bonding conductors as C3 and am happy to do so here too, but should I be coding the small earthing conductor more harshly ?
It will not conform with 542.3.1 as the earthing conductor will not be at least the size of the required size for the bonding conductor, but the bonding conductors are not of the required size anyway. The size does conform with the adiabatic equation for thermal constraints.

Could do with some helpful thoughts as I have a couple dozen of these to do and they look like they might all be of similar construction.

They are all looking at board upgrades anyway so this may be academic, but would like to be coding correctly.

 

[Deleted member 26818]

If you are ok with the bonding being undersized, why would you have a problem with the Earth being undersized?

 

[Andy78]

If you are ok with the bonding being undersized, why would you have a problem with the Earth being undersized?

No idea, I'm second guessing myself I suppose

 

[Strima]

Have you done the adiabatic to see if it is suitable?

 

[Andy78]

Have you done the adiabatic to see if it is suitable?

I have and it is.
Just the extra requirements of PME conditions made me doubt the coding requirements. It's not a situation I have come across in periodic inspection I don't think.

 

[7029 dave]

You will come across thousands of TNC-S earthing arrangements in the 70's with 6mm main earthing conductor, 60amp cut out, IMO I can't see anymore than c3.

 

[Andy78]

You will come across thousands of TNC-S earthing arrangements in the 70's with 6mm main earthing conductor, 60amp cut out, IMO I can't see anymore than c3.

Aye I think that's when these date from. I'm usually dealing with much older installs with TN-S, or TNC-S conversions of these. I tend to have a relatively small work area and don't see a lot of different supplies at all.

 

[westward10]

You will never know if the main protective bonds were correctly sized originally as the IEE Wiring Regulations which would have been in force during the 1970s, assuming we are talking this kind of era never quoted quoted main equipotential bonding sizes for TN-C-S systems, a small note stating the supplier should be consulted. If anyone says to me it was common practice and okay back in the 70s I say, prove it.

 

[Andy78]

Cheers guys, that's cleared my head on got me back on track

 

[Baker1988]

If the adiabatic is fine and it has no sogns of thermal damage then there is no problem really thats my two cents haha

 

[Richard Burns]

If the adiabatic is fine and it has no signs of thermal damage then there is no problem really that's my two cents ha ha

But what about the oft mentioned "disconnected supply neutral" when the load current will flow though the bonding conductors and cause a fire because they are too small!
I must admit I did do a few basic calculations and think 6mm² should be fine so long as there are not multiple houses connected after the neutral break and only one bonding conductor between them.

 

[Deleted member 26818]

But what about the oft mentioned "disconnected supply neutral" when the load current will flow though the bonding conductors and cause a fire because they are too small!
I must admit I did do a few basic calculations and think 6mm² should be fine so long as there are not multiple houses connected after the neutral break and only one bonding conductor between them.

Yep, but if the bonding is 6mm2, I doubt the Earth also being 6mm2 will make any odds.

 

[Richard Burns]

The earthing conductor would only take current during an earth fault; unless the neutral became disconnected before some of the PME earths to give an earth path, it will just be a floating conductor. The bonding will take the "heavy" load depending on the quality of the connection of the extraneous parts with earth.