TNC-S supply outdoors question.

[liddley]

Just a quick question on something I came across today. Had to replace a door on a metal clad box in a car park that vandals have broken off. Inside the Metal housing was a 100 A main cutout TNC-S , a Meter and a small C.U. with two MCB's, One for a car park pay and display meter directly behind the box and the other MCB which fed another C.U. in another metal housing fed by SWA in a duct in the flower bed the other side of the car parking area. This C.U. then fed lots of metal lighting columns via timer and contactor ect ect. ..
My question being is this not the same principle as exporting TNC-S from your house across to a shed/garage and have the potential for the Metal objects to become live if there is a problem DNO supply side.? Or am I over thinking this. Where is the equipotential zone. Is it just within the first 500×500 metal enclosure?

 

[Wilko]

Interesting. I haven't experience how this is designed in practice, but imagining from afar etc - I think swa armour for cpc should be ok, but likely not for bonding. So unless the down stream CU is set up as TT (gather not ?) then separate bonding likely required and is based on the incoming DNO neutral in accord with Table 54.8 - GN8 has an example on p70.

 

[liddley]

Yes the second c.u. is fed with a 2 core SWA using the armour as the cpu. Was just thinking when replacing the little earth bond fly lead from the box to the new box door that everything in this installation is metal the enclosures,the pay and display machine, ligthing columns ect. So fault current would try to find its way back through all these items if a fault occurred??

 

[Midwest]

Section 714 Outdoor Lighting Installations. Reg 714.411.203 refers to connection to distributors PME network.

 

[The Ghost]

If it is a main cut-out and DNO installed what is the problem?

 

[Andy-1960]

Have a look at Reg 559.10.3

 

[Midwest]

Have a look at Reg 559.10.3

What colour book are you looking in?

 

[Andy-1960]

What colour book are you looking in?

Yep your right!! Just looked in the yellow one.. ha ha

 

[Midwest]

Dooohhh!

 

[Andy-1960]

Dooohhh!

No need to rub it in!!