TN-C Earthing.............

[Marvo]

I know you're unlikely to come across TN-C earthing in the UK but I thought an installation I described in this post might make a nice trainee discussion.

The only power available in the village was in a small communal hall (more like a shed the size of a double garage) which served as their meeting place, school, hospital etc. It had a 2-wire supply on a straight concentric cable and going by the volt dip under a known load the supply cable must have been at least 3 km long.

There was a small CU with no earth and a single socket circuit and a light circuit installed. At every socket and light point there was a link between the neutral and the earth screws which made it a TN-C installation to all intents and purposes. They said they'd never used the electricity since it had been installed several years previously by an Italian charity organisation because it gave them shocks which was hardly surprising given the length of the supply cable and lack of actual earth.

Any comments on why the undersized or very long straight concentric supply cable would cause shocks to the users of the installation?

Any comments on the pro's or cons of a TN-C installation.

If, hypothetically speaking, you ever did come across a customer with a TN-C installation and it wasn't the DNO's responsibility to supply an earth what should / could be done to make it safer?

 

[Marvo]

Are the trainees all dead?

 

[Bobster]

It's probably not something they're taught Marvo.

TN-C is uncommon in the UK, and would never be connected like that. Only having the PE-N connection in one place.

However if it's a clue they're after VD and PD are places to start.

 

[curly]

Any comments on why the undersized or very long straight concentric supply cable would cause shocks to the users of the installation?

Electricity will take the path of the least resistance, as the cable was long and or undersized your body acts as a conductor to ground,

Any comments on the pro's or cons of a TN-C installation.

No comments

If, hypothetically speaking, you ever did come across a customer with a TN-C installation and it wasn't the DNO's responsibility to supply an earth what should / could be done to make it safer?
Fit an RCD
Mesure the fault current and fuse down to to achieve ADS at 50v
Convert to TT