TN-C-S or TN-S

[Guitarguy]

Kind of on topic.....

We requested a new supply for a caravan park a while ago, and made sure we requested TN-S, which the DNO paperwork did detail.

This is the service head they terminated......

It has since been replaced!

The scruffy gits!

I take pride in my installations, i would never leave anything in such a state!

 

[JohnW2]

We requested a new supply for a caravan park a while ago, and made sure we requested TN-S, which the DNO paperwork did detail.
This is the service head they terminated......
It has since been replaced!

I think I need more education about this area in which I am largely ignorant! That presumably is incoming TN-S, and would remain as TN-S had they not (rather messily) joined the neutral and earth? However, my question is ... is there ever a situation in which one would (or should) do that (join the L & E at service head), other, perhaps, than as a temporay fix in the case of an earth fault (although it's a bit hard to see how that could happen with split con)?

Kind Regards, John.

 

[Lectrician]

The DNO tend to use certain types of cable for all types of services, it saves stocking too many different sorts of cables and covers all arses so to speak. I guess the guy who came to fit the head just slapped it in as if it was PME without thought.

It should have been a head with a split neutral/earth block rather than a combined one.

What they actually did in the end was leave the head as it was, but put an earth block next to it with a 16mm earth from the bottom of the head looping into it. I guess they crimped the earths to the 16mm inside.

A few more:

This IS a TNS, using larger carriers than normal. WPD will only supply 80amp through the "standard" heads - if you want 100amp you have these fitted. This would be 100amp max, although the carriers can hold larger fuses, the metering is maxed to 100amp.

This is a TN-C-S supply using a 3 core waveform cable.

Difficult to see in this pic, but this is TN-S via a 4 core waveform cable (notice the extra blue than the pic above). This is a 250amp service.

This is a TN-S on another caravan park - difficult to tell with the cover on...

Here is a domestic TN-S.

 

[STI]

That last one on the domestic suprised me.I would have classed that as TNCS just by looking at it with the cover on.

 

[JohnW2]

The DNO tend to use certain types of cable for all types of services, it saves stocking too many different sorts of cables and covers all a**es so to speak. I guess the guy who came to fit the head just slapped it in as if it was PME without thought.

Thanks. Are you implying that they use split con for TN-C-S supplies (presumably with N & E joined at t'other end)?

A few more:

Many thanks. That's very educational.

Kind Regards, John.

 

[Lectrician]

That last one on the domestic suprised me.I would have classed that as TNCS just by looking at it with the cover on.

A trained eye can usually tell by the diameter of the cable if it is straight or split concentric.

Thanks. Are you implying that they use split con for TN-C-S supplies (presumably with N & E joined at t'other end)?

Not quite. On standard single phase services they will generally use straight concentric, L+N only.

On larger supplies, or supplies that are singular from a dedicated transformer, or a transformer feeding just a few properties, they may use cables which above and beond what is required. They do this because they have it, and because it covers all bases.

Another example would be an 800amp supply, the DNO installed four x 4 core waveform cables, each cable was treated as a single core - the 4 cores stripped and terminated into a single lug. The waveform outer was used as the earth and supplemented with an additional earth too.

 

[studentspark]

Great thread, really interesting.

 

[kai]

This is a TNCS supply fed from a substation across the road.

 

[JohnW2]

Thanks. Are you implying that they use split con for TN-C-S supplies (presumably with N & E joined at t'other end)?

Not quite. On standard single phase services they will generally use straight concentric, L+N only.

That's what I thought - hence my question.

On larger supplies, or supplies that are singular from a dedicated transformer, or a transformer feeding just a few properties, they may use cables which above and beond what is required. They do this because they have it, and because it covers all bases.

Thanks again. I guess that makes sense. This seems to me (as in the piccie which started this thread) to make the distinction between TN-S and TN-C-S a bit more 'grey' than I had previously considered.

Kind Regards, John.

 

[securespark]

A trained eye can usually tell by the diameter of the cable if it is straight or split concentric.

I'll second that. The split-con (TN-S cable) is appreciably fatter than the straight.