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Discuss TN-S earthing query in the Electrical Forum area at ElectriciansForums.net

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Hi everyone,
This might be a silly question but I have been asked to look at job where they would like a new garage supply, its a old property with the re-wireable fuse board but previously someone has tapped off the meter to an additional RCD unit which was used for a shower (no longer required). They do plan on doing a board upgrade, but at the moment they could do with power in the garage. So my thought are i could use the RCD unit to feed the garage and use a main switch consumer unit in the garage for the time being. My question is in regards to the TN-S, it looks like a old supply with stranded cable with no insulation? Would this earth still be ok to use providing the earthing to the RCD unit is 16mm? Or would the DNO have to upgrade their earth first?
Thanks
 

Dartlec

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Hi everyone,
This might be a silly question but I have been asked to look at job where they would like a new garage supply, its a old property with the re-wireable fuse board but previously someone has tapped off the meter to an additional RCD unit which was used for a shower (no longer required). They do plan on doing a board upgrade, but at the moment they could do with power in the garage. So my thought are i could use the RCD unit to feed the garage and use a main switch consumer unit in the garage for the time being. My question is in regards to the TN-S, it looks like a old supply with stranded cable with no insulation? Would this earth still be ok to use providing the earthing to the RCD unit is 16mm? Or would the DNO have to upgrade their earth first?
Thanks
As long as the Ze reading is fine then nothing wrong with using it. Those stranded uninsulated cables are still pretty common, as are the braided tape type. (They are often soldered (not exactly, but can't think of the right word) to the incoming cable and rather more reliable than the ones that have had a bonding clamp added at some point)

Is there a separate earth bar to act as the MET? If not, that's the best way to set it up, with 16mm to each CU (or what ever is there currently if it's appropriate) - that way if they ever do upgrade the earth there will be no additional wiring to do.

You can request an upgrade and if the head allows an easy PME upgrade then they will come out and do it without too many problems. Otherwise if the head is fine and not ancient they'll probably leave it as it is unless you are requesting a fuse upgrade.

Nothing wrong in principle with using the shower unit. If the garage is separate and running SWA to it then better to have the RCD at the far end, but since it's already there makes sense to reuse it....
 

ipf

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Incoming earth no problem, as long as it tests OK,
If they've been naughty and 'tapped off the meter' direct, it sounds like Henleys would be practical.
 
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As long as the Ze reading is fine then nothing wrong with using it. Those stranded uninsulated cables are still pretty common, as are the braided tape type. (They are often soldered (not exactly, but can't think of the right word) to the incoming cable and rather more reliable than the ones that have had a bonding clamp added at some point)

Is there a separate earth bar to act as the MET? If not, that's the best way to set it up, with 16mm to each CU (or what ever is there currently if it's appropriate) - that way if they ever do upgrade the earth there will be no additional wiring to do.

You can request an upgrade and if the head allows an easy PME upgrade then they will come out and do it without too many problems. Otherwise if the head is fine and not ancient they'll probably leave it as it is unless you are requesting a fuse upgrade.

Nothing wrong in principle with using the shower unit. If the garage is separate and running SWA to it then better to have the RCD at the far end, but since it's already there makes sense to reuse it...
Thanks for your reply.
Yes theres is a MET there, I was planning on doing with the earths it made sence to me but just wanted to confirm it 🙂

The RCD unit would only be a until they upgrade the board then the garage can have a RCD main switch, just thinking of the safest and best way to do it at at the moment.
 

telectrix

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Thanks for your reply.
Yes theres is a MET there, I was planning on doing with the earths it made sence to me but just wanted to confirm it 🙂

The RCD unit would only be a until they upgrade the board then the garage can have a RCD main switch, just thinking of the safest and best way to do it at at the moment.
your plan looks good to me.henley block the tails if not already done. just make sure the armour of the SWA is earthed. myusualmethod would be to use 3 core SWA and use both the 3rd conductor and the armour as cpc. if it;s pme, though, you'd need equivalent of 10mm for bonding any extraneous parts in the outbuilding.
 
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Incoming earth no problem, as long as it tests OK,
If they've been naughty and 'tapped off the meter' direct, it sounds like Henleys would be practical.
Thank you, completly agreed. Ideally that would be a better situation, but there isn't a isolator there so would mean pulling the main fuse out, which I assume the previous person had done
 
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your plan looks good to me.henley block the tails if not already done. just make sure the armour of the SWA is earthed. myusualmethod would be to use 3 core SWA and use both the 3rd conductor and the armour as cpc. if it;s pme, though, you'd need equivalent of 10mm for bonding any extraneous parts in the outbuilding.
Hi tel,
I am pretty sure this is a TN-S, is there anyway to see if it has been converted? I have a picture but it isn't the best.

Thats great thank you 🙂20210504_162842.jpg
 

Taylortwocities

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Looks like TNS. Not converted to anything else.
Cannot see from the photo how the main earth is connected to the supply cable sheath. Has it been sweated on?

PS horrible big holes in the top of that Wylex mini CU.
Not IP compliant - needs sorting
 
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Looks like TNS. Not converted to anything else.
Cannot see from the photo how the main earth is connected to the supply cable sheath. Has it been sweated on?

PS horrible big holes in the top of that Wylex mini CU.
Not IP compliant - needs sorting
I knew someone would spot that haha, the wylex cu is not being used the 6mm twin and earth is disconnected and no power going to the cu so I will remove that.
It is at the back of the cable, is 'sweated on' like soldered?
 

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