Tn-c-s how the combined bit works

[Steviet]

I need a dummy's explanation of how the earth and neatral are combined and how they are split. Cheers

 

[mechelec]

At the supply sub station the transformer neutral point is connected to earth via rods. the LV distribution cable has its neutral and earth (lead sheath if applicable) connected at the LV ditribution pillar to the same earth rods. At joints along the length of the supply cable, or every 4th pole on OH supplies, earth rods are used at set distances to tie the neutral to earth (PME). At the customers cutout (PME) a concentric type cable may be used with centre phase and outer neutral connected to the cutout. The customers earth and neutral will come from the same connector block. They are then separated in the customers instalation and must not be combined after this point.
If a paper lead type cable is used and is PME'd then the lead and neutral will be combined often in a henley block. Again the customers neutral and earth will be separated after this point.
If the lead sheath and neutral are not combined it is a TN-S system

 

[Spudnik]

 

[Steviet]

The above two has answere everything I could have asked for cheers !

 

[mechelec]

A picture beats my waffle any day.

 

[GLENNSPARK]

you can have PNB n all....Protective Neutral Bonding....like PME but without the earth tappings at regular points as described above by Jason...this is more for single consumer use.......

 

[Engineer54]

At the supply sub station the transformer neutral point is connected to earth via rods. the LV distribution cable has its neutral and earth (lead sheath if applicable) connected at the LV ditribution pillar to the same earth rods. At joints along the length of the supply cable, or every 4th pole on OH supplies, earth rods are used at set distances to tie the neutral to earth (PME). At the customers cutout (PME) a concentric type cable may be used with centre phase and outer neutral connected to the cutout. The customers earth and neutral will come from the same connector block. They are then separated in the customers instalation and must not be combined after this point.

If a paper lead type cable is used and is PME'd then the lead and neutral will be combined often in a henley block. Again the customers neutral and earth will be separated after this point.
If the lead sheath and neutral are not combined it is a TN-S system

Not where i come from.. Where an old TN-S system PILS cable has been PME'd, the earth bond to the lead sheath is cut off/removed. The N/E connection is provided purely at/from the cut-out. Even the the roded neutral PME'd joints on the main cable string don't incorporate the lead sheath. Not sure what happens at the local Distribution Transformer though!!...

 

[mechelec]

Not where i come from.. Where an old TN-S system PILS cable has been PME'd, the earth bond to the lead sheath is cut off/removed. The N/E connection is provided purely at/from the cut-out. Even the the roded neutral PME'd joints on the main cable string don't incorporate the lead sheath. Not sure what happens at the local Distribution Transformer though!!...

Im suprised at that, if the lead sheath to earth connection at the sub became detached or more likely not bonded correctly in a joint, the exposed lead sheath in a customers property could be at a higher potential than earth and be a shock/fire risk. Bonding the lead at PME'd joints and at cutouts keeps everything at the same potential. That said if you get a neutral fault the lead would be carying the neutral current (which would still be preferable to open circut neutral faults on the distribution network)