Earthing and bonding

[westward10]

Don't understand the question.

 

[Wilko]

If I've understood correctly...
For TNS and TT - line conductor over 35mm bonding goes to 16mm, from table 54.7 and reg 544.1.1
For TNCS - DNO neutral conductor over 35mm bonding goes to 16mm, from reg 544.1.1 and table 54.8.

 

[westward10]

I see now, don't see relevance of question though.

 

[Rocboni]

Not all TNCS supplies are PME but all PME supplies are TNCS so how do you know if it's PME, will the DNO always put a sticker on?

 

[Wilko]

Not all TNCS supplies are PME but all PME supplies are TNCS so how do you know if it's PME, will the DNO always put a sticker on?

I had not heard this ... I look in BYB section 312.2.1 fig 3.9 where TNCS and PME seem to be the same thing (?).

 

[Rocboni]

Just what I've read elsewhere, so not sure, I think you might be right though.

I suppose you could have a on site Tx which TNCS supply with no multible earthing. So if no tx on site then the TNCS supply will always be PME?

 

[westward10]

TN-C-S is generally considered PME with some exceptions, the example you give could be one.

 

[DPG]

Page 47/48/49 of GN8 explain (and show) the difference between PME and PNB.
Daz

 

[Deleted member 26818]

I see now, don't see relevance of question though.

Quite simple.
By the time the CSA of the armour is sufficient to offer the equivalent conductance of 10mm2 copper, you need the equivalence of 25mm2 copper.
As such SWA is never suitable for bonding.

 

[westward10]

Nope still don't know what you are getting at, armour can be used for supporting bonding.

 

[Deleted member 26818]

Don't understand why you're having trouble with this?
The conductance ratio between steel and copper is about 9:1.
By the time you've found an SWA cable where the armour has a sufficient CSA to be a bonding conductor, you will require a larger bonding conductor.

95mm2 SWA has armour which has the equivalent conductance of a 10mm2 copper conductor. Unfortunately a 95mm2 SWA cable, would where PME conditions apply require a bonding conductor with the equivalent conductance of a 35mm2 copper conductor.

 

[westward10]

These cables would be used for supplies to other buildings where bonding would be required, the size of main bonding has already been decided at the DNO source. We are not discussing DNO supply cables.

 

[sparksburnout]

These cables would be used for supplies to other buildings where bonding would be required, the size of main bonding has already been decided at the DNO source. We are not discussing DNO supply cables.

In this case then, what's to stop you using a 4C 10mm SWA (even if you don't need one), and using the 4th core for the Bonding conductor?

 

[westward10]

In this case then, what's to stop you using a 4C 10mm SWA (even if you don't need one), and using the 4th core for the Bonding conductor?

Nothing.

 

[Deleted member 26818]

These cables would be used for supplies to other buildings where bonding would be required, the size of main bonding has already been decided at the DNO source. We are not discussing DNO supply cables.

Lol.
What does that mean?
Are you suggesting that this supply to another building would be larger than the DNO supply at source?

 

[westward10]

Lol.
What does that mean?
Are you suggesting that this supply to another building would be larger than the DNO supply at source?

Are you trying to get a rise or are you just not understanding.

 

[Deleted member 26818]

I think it is you that is having a problem with understanding.
If the main incomer requires 10mm2 bonding conductors, that would suggest the supply conductors are no greater than 35mm2.
Why would you then use 95mm2 SWA for a sub main?

 

[westward10]

Getting a rise then.

 

[Toneyz]

I think it is you that is having a problem with understanding.
If the main incomer requires 10mm2 bonding conductors, that would suggest the supply conductors are no greater than 35mm2.
Why would you then use 95mm2 SWA for a sub main?

length of run ,volt drop earth loop imp. etc

 

[westward10]

I think it is you that is having a problem with understanding.
If the main incomer requires 10mm2 bonding conductors, that would suggest the supply conductors are no greater than 35mm2.
Why would you then use 95mm2 SWA for a sub main?

I have no idea why you keep referring to the supply conductor size, the point is can a sub main swa cable support bonding when the armour is used as the earth. This will nearly always apply to a three phase supply where the minimum size to support bonding would be 50.0. In this day and age people nearly always use three core cable utilising a core as the cpc for single phase supplies. Otherwise it would have to be 95.0 for a two core.