Earthing arrangement when moving consumer unit far away from TN-S supply?

[ZEDEZ]

I've been doing a lot of research, and am hearing a lot of conflicting information on this subject. Currently working on an important job and want to get this perfect, and the time is coming soon to connect the new consumer unit up to the supply, so would be interested to get some more feedback here.

So to put it in hypothetical terms, lets say you had a 100 amp TN-S supply & meter located on the outside of the house, and the consumer unit were to be relocated in a room within in the house, 5 - 10 m away from the supply, with the cable disappearing underground. How would you do it in the most efficient and compliant way possible?

Here's what I'm thinking I'd do:

Install 100 amp metal clad switched fuse next to meter. Meter tails go into this. To get from here to the new CCU I'd use 2 core 25mm SWA, glanded and Earth nutted to switched fuse enclosure, with a 16mm copper flying lead connecting Earth nut to MET. The same same gland / Earth nut arrangement would apply at the CCU, connecting the Earthing bar to SWA armour. So no unsightly additional CPC tagging along with the SWA, and no unnecessary re purposing of a core of 3 core SWA.

Assuming disconnection times / adiabatic equations etc. all work out (which so far given optimal circumstances seem that they do), can anyone see any problems with this arrangement, or is there a better way? Also - on the schedule of results, if using this arrangement, what would the e̶a̶r̶t̶h̶i̶n̶g̶ ̶c̶o̶n̶d̶u̶c̶t̶o̶r̶ CPC of the distribution circuit (thanks for clarification of terms there davesparks) material be listed as, given that it's a combination of copper and steel?

Generally interested to hear how you'd do it / have done it, and reasons why. I am inexperienced but very keen to really get to grips with best practice & the theory behind it.

EZ

 

[Deleted member 9648]

Whats your problem with a 3c SWA?

 

[davesparks]

The earthing conductor would be the 16mm copper which connects the installation to the means of earthing.

 

[Andy78]

Where will your bonding cables be terminating ?

 

[ZEDEZ]

It just seems unnecessary some of the time. If the armour is adequate to use as an earthing conductor, why add unnecessary copper to the cable with an additional core?

Also, 2 core SWA is coloured BROWN / BLUE. 3 core requires over sleeving if used with a single phase supply.

I've got nothing against using 3c SWA per se, neither 4 core or 5 core ... What I am against is doing things in an inefficient manor and the waste (including time) associated with said inefficiency.

 

[davesparks]

The armour will not be the earthing conductor, it will be the cpc of the distribution circuit.

 

[ZEDEZ]

MET at the supply, located on outside of the house, same place the SWA eventually terminates (via Earth nut & copper fly lead of course).

So the earthing route from CU to Earth is, CU Earth Bar -> 16mm copper fly lead -> Earth nut -> steel armour -> Earth nut -> 16mm copper fly lead -> MET -> DNO Earth.

 

[ZEDEZ]

The armour will not be the earthing conductor, it will be the cpc of the distribution circuit.

Thanks davesparks, I have edited my original post to clarify

 

[Pete999]

Whats your problem with a 3c SWA?

What he said^^^^^^^^^

 

[Simonslimline]

What about post 4?

 

[Pete999]

What about post 4?

Good point,

 

[bigspark17]

3core swa everytime for me.. Also get ur zdb reading as low as possible! Seems lazy doing 2c and unprofesional.. What part of country are you, i live by coastline and seasalt in the air can do some serious damage to swa glands overtime especially as ur terminating in outside box!

 

[davesparks]

3core swa everytime for me.. Also get ur zdb reading as low as possible! Seems lazy doing 2c and unprofesional.. What part of country are you, i live by coastline and seasalt in the air can do some serious damage to swa glands overtime especially as ur terminating in outside box!

What is unprofessional about using a cable in the way it was designed to be used. Do you think it's coincidence that 2 core SWA has core colours suitable for single phase and 3 core doesn't?
You are insulting myself and all of the other electricians here who have used 2 core cables by stating that it is unprofessional.

Glands rotting in the sea air suggest that the wrong glands have been used.

 

[ZEDEZ]

3core swa everytime for me.. Also get ur zdb reading as low as possible! Seems lazy doing 2c and unprofesional.. What part of country are you, i live by coastline and seasalt in the air can do some serious damage to swa glands overtime especially as ur terminating in outside box!

I'm near London, but I hear what you're saying, I'm always amazed with the corrosion levels in coastal places. I was recently on a Welsh coast, visited a city car park and was looking at the metal conduit for the wiring in there. The whole installation looked like it'd been installed on an oil rig out at sea for 20 years!

But back to the SWA, my thinking on this is in line with davesparks, and there could be an argument for having an additional CPC whether core or external in a harsh environment, as an alternative / backup to the armour CPC (though as far as I'm aware, in these situations the copper has to be able to take the whole fault current on it's own, due to the fact that the conductivity of copper is much higher).

 

[Simonslimline]

I'm near London, but I hear what you're saying, I'm always amazed with the corrosion levels in coastal places. I was recently on a Welsh coast, visited a city car park and was looking at the metal conduit for the wiring in there. The whole installation looked like it'd been installed on an oil rig out at sea for 20 years!

But back to the SWA, my thinking on this is in line with davesparks, and there could be an argument for having an additional CPC whether core or external in a harsh environment, as an alternative / backup to the armour CPC (though as far as I'm aware, in these situations the copper has to be able to take the whole fault current on it's own, due to the fact that the conductivity of copper is much higher).

Bonding?

 

[bigspark17]

For the sake of say £20 on 5-10M run.. It really is a no brainer lads.! Are u seriously pricing jobs that close.. I pride myself on being a local spark and here for the long run on the local work i do! not it complies now and sod the future degrading and then its some1 else's problem! Didnt mean to offend you davesparks non ment, but reading back i see my bluntness!

 

[ZEDEZ]

Bonding?

In the original scenario? As said in reply to Andy78:

MET at the supply, located on outside of the house, same place the SWA eventually terminates (via Earth nut & copper fly lead of course).

So the earthing route from CU to Earth is, CU Earth Bar -> 16mm copper fly lead -> Earth nut -> steel armour -> Earth nut -> 16mm copper fly lead -> MET -> DNO Earth

 

[sam400]

Hi is it xlpe or pvc insulated 2c your planning on using?

sam

 

[ZEDEZ]

For the sake of say £20 on 5-10M run.. It really is a no brainer lads.! Are u seriously pricing jobs that close.. I pride myself on being a local spark and here for the long run on the local work i do! not it complies now and sod the future degrading and then its some1 else's problem! Didnt mean to offend you davesparks non ment, but reading back i see my bluntness!

"...and am hearing a lot of conflicting information on this subject."

Glad we're thrashing it out

 

[ZEDEZ]

Hi is it xlpe or pvc insulated 2c your planning on using?

sam

Unsure ... In this scenario what are the differences between the two?