TN-S Earthing

[Gardner]

Are earth rods or earth electrodes required for TN-S supply?

 

[Gardner]

If there is an earthing system of TNCS or TNS then the supply earth is provided by the distribution network operator, it is not permitted for us to create a TNCS system by making a N-E link.
The earth must either be supplied from the public supply system by the DNO or, if an earth is not provided by the DNO, then we can install an earth electrode.

If there is no earth provided at the installation then one can request an earth provision from the DNO, but they do not need to provide one, e.g. if the network conditions are not suitable or the installation may present danger with a TNCS system.

What do you mean the DNO will provide an earth? My understanding is the DNO will either proved 3 wires (TN-S), 2 wires with the incoming neutral bonded (TN-C-S) or 2 wires with neither conductor supposed to be earthed at the premises (TT supply).

Or you mean the N-E link must only be made by the DNO and not the electrician?

 

[Engineer54]

What do you mean the DNO will provide an earth? My understanding is the DNO will either proved 3 wires (TN-S), 2 wires with the incoming neutral bonded (TN-C-S) or 2 wires with neither conductor supposed to be earthed at the premises (TT supply).

Or you mean the N-E link must only be made by the DNO and not the electrician?

That's the one!!

 

[Gardner]

That's the one!!

Ok that make sense now. Thanks Now with that said, this equates to an electrician not being allowed to touch the incoming service head as that is where the N-E bond is made?

 

[Richard Burns]

Yes we are not allowed to touch bits that our not ours (or our customers)
A little responsibility diagram from one of our DNO's detailing who is allowed to deal with what at the intake position.

 

[Gardner]

Thanks, awesome diagram! So basically the DNO dictates TT, TN-S, ect.

 

[davesparks]

So if lets say I had a home with no rebar in the foundation, and the water line coming in was plastic with no gas on the property, I can just run a jumper from the neutral to the main earthing terminal and be code complaint?

An earthing electrode only serves the function of fault clearing as in a TT network?

No, you must not join earth to neutral at any point in the installation! The DNO will either provide you with an earthing terminal, or not, any linking of N and E will be done by the DNO.

The only time you will have your own N-E link is if you have your own private transformer or generator.

 

[davesparks]

Ok that make sense now. Thanks Now with that said, this equates to an electrician not being allowed to touch the incoming service head as that is where the N-E bond is made?

The N-E connection is made at the substation. The DNO cables will have a CNE conductor in them which is connected to earth electrodes periodically. The DNO will either connect your earthing conductor to their CNE terminal or remove a knockout in the side of the head which allows you access to one of the terminals in the CNE block so that you can connect your earthing conductor.

 

[Gardner]

The N-E connection is made at the substation. The DNO cables will have a CNE conductor in them which is connected to earth electrodes periodically. The DNO will either connect your earthing conductor to their CNE terminal or remove a knockout in the side of the head which allows you access to one of the terminals in the CNE block so that you can connect your earthing conductor.

CNE? IS that an SWA cable shield?

 

[davesparks]

CNE? IS that an SWA cable shield?

Combined Neutral and Earth

 

[ipf]

CNE? IS that an SWA cable shield?

Combined neutral earth.

edit. late......snap!!

Cable Network Egypt, then.

 

[Gardner]

Combined Neutral and Earth

OK, that would make it a MEN system.

In a TT system do DNOs usually earth the neutral repeatedly or only at the 11-400Y substation? Of course this would not matter at the customer but just trying to get a sense of whats going on.

 

[spark 68]

OK, that would make it a MEN system.

In a TT system do DNOs usually earth the neutral repeatedly or only at the 11-400Y substation? Of course this would not matter at the customer but just trying to get a sense of whats going on.

Have a look at this attached pdf,

 

[davesparks]

OK, that would make it a MEN system.

In a TT system do DNOs usually earth the neutral repeatedly or only at the 11-400Y substation? Of course this would not matter at the customer but just trying to get a sense of whats going on.

Never heard of MEN as an earthing arrangement, it is a TNCS system and may be PME.

What the DNOs get up to is entirely up to them, if the supply was designed as a TT system then you'd expect it to only be earthed at the substation transformer yes. But if it has been made TT because the DNO have declined to make an earth connection available to the customer it could be anything.
It could also be that the DNO have made their TNCS earth connection available but the regulations have prohibited its use in the installation.

 

[Gardner]

Have a look at this attached pdf,

That clears up a lot! Thanks

One question that stands out. One page 3 where a TN-C-S system is shown it says "Additional source electrode" What do they mean by that? Is this electrode part of the DNO or electrician supplied connected to the MET?

 

[davesparks]

That clears up a lot! Thanks

One question that stands out. One page 3 where a TN-C-S system is shown it says "Additional source electrode" What do they mean by that? Is this electrode part of the DNO or electrician supplied connected to the MET?

That is an example of one of the many Earth electrodes which would be connected along the length of a PME distribution cable (on the DNO side)

But an electrode can be installed by the electrician and connected to the MET if they deem it to be necessary. This is common practice in some countries and a requirement in others (Ireland springs to mind for this)