Earth requirements for TN-S with RCD 30ma main switch

[Golden Graeme]

Hi,

I am newly qualified and didn't really cover this scenario.

I am a little unsure, so some advice would be great.

I have an old installation that has a 6mm earth cable from the DNO TN-S to the consumer unit earth bar.

The consumer unit main switch is a combined 100A and 30mA switch.

This does not comply with earthing requirements as the earth cable isn't 16mm.

Is the RCD Main switch sufficient to cover the disconnect

Also there is no supplementary bonding to gas and water extranious conductors, is this also cover by the additional disconnect of the RCD?

 

[The Ghost]

Well first off TNS, I personally am too scared to mess with the connection on the sheath of the DNO cable. They are known to explode when tightening it up especially old supplies as when you tighten the earth it can cause the L-N to short. So the DNO would connect a 16mm² to it instead of you. People may tell you otherwise but I would say don't take the chance, let the DNO.
If you did an adiabatic calc you may find 6mm² is adequate however whenever I say this on site 10 other electricians start shouting NO you gotta go by the regs etc.
I am not clear about the Protective/switching devices, a photo speaks a thousand words. Of course you would need to upgrade bonding to services. And extraneous parts is a bit of a tricky area, what is extraneous in the installation? The term "cover the disconnect" is hard to envisage what you are asking there?

 

[Golden Graeme]

Here are a couple of the pics showing DNO and consumer unit.

 

[Wilko]

Hi - IMHO the main protective bonding conductors to water and gas are still required. Using 543.1.1, the size of the protective conductor can be selected as 16mm (table 54.7) or calculated from eqn in 543.1.3 . Its possible that 6mm will calculate as OK, depending on house fuse size and prospective fault current. Also a visual check of the 6mm to confirm its not been heat damaged in the past. (But I do feel better with the bigger cable )

Edit : just read V's post and seen the pics ... yes, I would get DNO to upgrade if required.

 

[The Ghost]

So what are you supposed to do in the installation? Great pics btw. Not to sure about that black tape on the line either, looks very poorly wired.

 

[telectrix]

where does that cable in tern 8 of the earth bar go to? it looks like 10mm main bonding.

 

[Golden Graeme]

Garage to bedroom conversion
Minor work.
My work is to :-
Extend ring to add a couple of sockets and sw spur outlet for electric heaters.
Split single lighting cct to two new rooms individually switched and add smoke and CO2 detectors.

 

[Golden Graeme]

where does that cable in tern 8 of the earth bar go to? it looks like 10mm main bonding.

Just large sleeving on lighting cpc.

 

[Golden Graeme]

Main earth maybe 4mm !

 

[telectrix]

and whoever did that CU "upgrade" wants handcuffing to Diane Abbot.

 

[Deleted member 26818]

Umm, when did this requirement for 16mm main earth come in?

 

[Golden Graeme]

I've now got the DNO on the case, they are going to arrange a site visit to rectify the issue.

 

[Octopus]

Umm, when did this requirement for 16mm main earth come in?

The pretty picture in the OSG I imagine....

 

[Deleted member 26818]

So no requirement for 16mm then?

 

[Golden Graeme]

So no requirement for 16mm then?

The DNO is going to come out and rectify the main earth conductor.
They agree on the phone that's it's under sized but need to make an appointment to upgrade it.

Looks like sometime early November

 

[Golden Graeme]

So no requirement for 16mm then?

The DNO is going to come out and rectify the main earth conductor.
They agree on the phone that's it's under sized but need to make an appointment to upgrade it.

Looks like sometime early November.

The household haven't had shocks etc, so minimal risk, also all circuits are protected by a 30mA RCD.

 

[Pat H]

I'd upgrade the main earth to 16mm. Then 10mm for the supplementary bonding to gas water.
I didn't see a MET so you should drop one in.

 

[Golden Graeme]

I'd upgrade the main earth to 16mm. Then 10mm for the supplementary bonding to gas water.
I didn't see a MET so you should drop one in.

The DNO is due out in a few weeks to change the main earth cable which currently goes straight in to the CU.

I have added a 10mm make bonding to gas services, I can't find the water in Tom the house !!!

 

[Leesparkykent]

What is the Ze?

 

[HandySparks]

I didn't see a MET so you should drop one in.

Perfectly acceptable to use the earth bar in the CU as the MET.