TT system - Reg 411.5.1

[Paul505]

Just looking at the second part of this reg with the statement " The neutral point or the midpoint of the power supply system shall be earthed. If the neutral point or midpoint is not available or not accessible, a line conductor shall be earthed"
My question is... I assume they are talking about the connection at the transformer sub station and if so why did they feel the need to add this, as I haven't seen it there before now?

 

[buzzlightyear]

reg 411.5.1 it states every exposed conductive part is provided by a single PPD shall connected ,via the main earthing to the common earth terminal .

 

[Wilko]

Hi - yes that is a new sentence in the 18th. Like you, I think they must be referring to the transformer mid point being earthed at origin, as per fig 3.10, which has not changed. Sorry, I’m at a loss why they’ve added it too.

 

[Strima]

Added to add confusion.

 

[static zap]

Added to add confusion.

Neutral is a "Line" conductor... but have you got one!
(Looking at Buzz'es Diagram)

 

[davesparks]

My question is... I assume they are talking about the connection at the transformer sub station and if so why did they feel the need to add this, as I haven't seen it there before now?

It has probably come as a result of international harmonisation,

 

[Charlie_]

Neutral is a "Line" conductor... but have you got one!
(Looking at Buzz'es Diagram)

No it isn’t

 

[Charlie_]

The regs have made another typo

 

[static zap]

No it isn’t

Does it need a name then like "star-point"... ?
Or is that half the battle in a world of Non-verbal Icons.

 

[Charlie_]

Sorry, I meant neutral isn’t a line conductor

 

[Deleted member 26818]

Just looking at the second part of this reg with the statement " The neutral point or the midpoint of the power supply system shall be earthed. If the neutral point or midpoint is not available or not accessible, a line conductor shall be earthed"
My question is... I assume they are talking about the connection at the transformer sub station and if so why did they feel the need to add this, as I haven't seen it there before now?

This relates to portable generators.

 

[buzzlightyear]

I do you know why the a88 holes write the books and put the appendix at the back of the books is beyond me. when you are looking for things ,they has well right it in Chinese. or Arabic .

 

[Strima]

I do you know why the a88 holes write the books and put the appendix at the back of the books is beyond me. when you are looking for things ,they has well right it in Chinese. or Arabic .

It's like trying to read one of your posts Buzz...

 

[buzzlightyear]

It's like trying to read one of your posts Buzz.

sticks and stones will break me bones ,but the words will never hurt me .

 

[davesparks]

This relates to portable generators.

TT isn't used with portable generators.

 

[davesparks]

Portable generators use TNS earthing. TT with a portable generator would be pointless.

 

[Deleted member 26818]

Portable generators use TNS earthing. TT with a portable generator would be pointless.

How would TN-S work if there’s no reference to earth?

 

[static zap]

...why...(do THEY) put the appendix at the back of the books.....

He who gets bored 1st learns the least ...
(I always look at the back -before leaving !)
Patience grass hopper !
...Some times it's an addendum errata....
Bits that they got wrong..

 

[buzzlightyear]

He who gets bored 1st learns the least ...
(I always look at the back -before leaving !)
Patience grass hopper !

which one is you stat .

 

[Paul505]

Thanks for all the replies.... much appreciated!
I fully understand the principles of a TT system, but thanks to those who added anyway, just not the unnecessary insert in the regs and for what reason this is helpful to anyone, to be honest.

 

[davesparks]

How would TN-S work if there’s no reference to earth?

If there is no reference to earth, and it is intentionally designed to be this way then it would be IT, It won't be TT.
If there is no reference to earth when they is supposed to be then it will be dangerous.

 

[Deleted member 26818]

If there is no reference to earth, and it is intentionally designed to be this way then it would be IT, It won't be TT.
If there is no reference to earth when they is supposed to be then it will be dangerous.

Yes, which is why they are saying, reference one of the line conductors to earth.

 

[Bobster]

How would TN-S work if there’s no reference to earth?

It's not TT due to the fact that the reference point isn't transferred through the mass of earth. I.e from a rod at a house to the DNO tx.

A generator with a Rod is TN-S as in all intents and purpose it can be treated as a transformer secondary. Albeit with a low potential earth fault current.

You wouldn't rod a genny and then run phases to whatever you were feeding without a CPC just to install a second rod there. (This instance it would be TT)

 

[stevethesparks]

Sorry to resurrect this thread but has the original question ever been answered elsewhere?

 

[UKPN]

Just looking at the second part of this reg with the statement " The neutral point or the midpoint of the power supply system shall be earthed. If the neutral point or midpoint is not available or not accessible, a line conductor shall be earthed"
My question is... I assume they are talking about the connection at the transformer sub station and if so why did they feel the need to add this, as I haven't seen it there before now?

Its all part of the wiring regs poking their nose into DNO matters. Just disregard it.

 

[Julie.]

Its all part of the wiring regs poking their nose into DNO matters. Just disregard it.

Not really.

Many end users have their own transformers taking in at a mv or hv supply

To them, the earthing arrangements are very much to do with them, and not the DNO.