Type of Installation

[Electro-tech]

Hi Guys, I would like your take on this Installation. The Supply source is in a switch room & the cable is terminated at the rear of Switch Fuse Disconnector, see photos. The intake at the Distribution Panel is also shown. You will see that the Neutral is connected to the panel metal work. The cable is glanded to the top of the same panel. Assuming the earth path is from gland to gland at either end of the cable. Without further investigation as to the earth terminations at a glance would you say this is unusual linking the neutral to earth.

 

[DPG]

Is that TNC then?

 

[Electro-tech]

Is that TNC then?

I guess so, all the exposed conductive parts are connected via the metal work in the Distribution Panel & the neutral bar. The Earth via the armour of the supply cable back to the source metalwork which is strapped to the incoming neutral as photo.

 

[DPG]

I'm sure someone more knowledgeable than me will have some wise words.....

 

[Lucien Nunes]

What is the source of supply? Public network / on-site transformer / generator? Where is the meter relative to that ISCo neutral block?

 

[Electro-tech]

What is the source of supply? Public network / on-site transformer / generator? Where is the meter relative to that ISCo neutral block?

The source of supply is TNS I think, a 1200 Amp TP & N intake supplied from Public network into Main Power Room with meter then 3TP & N sub main supply to Distribution Panel in small Switch Room. Length of cable run is around 40 Meters.
I have a ELI of 0.06 at Neutral to metalwork bond on the DB/panel.

 

[westward10]

So are your pics the downstream dist panel in the small switch room.

 

[Electro-tech]

So are your pics the downstream dist panel in the small switch room.

The photo with the Isco Neutral Block is in the small switch room & the Switch Fuse Disconnector with the rear view of the cable gland termination is 40 meters away at the main intake at DNO Source in other 2 photos.

 

[westward10]

If that cable is definitely not part of the DNO supply that neutral should not be bonded to earth. Looks like it has been there a long time, 50-60 years I should imagine.

 

[Electro-tech]

If that cable is definitely not part of the DNO supply that neutral should not be bonded to earth. Looks like it has been there a long time, 50-60 years I should imagine.

The supply is definitely fed from the main Busbars in the old Slatter switchgear which is then distributed around the Business Park. we have 3 more Switchrooms.
The supply in question is the only one with the neutral/Earth link to the Panel.
I will now have to calculate the CSA of the Steel wire Armour of the cable to make sure it is of adequate size, as with the link removed this will be the Main Earth Conductor.

 

[westward10]

It is possible at some point that was DNO equipment judging by the bare earth and and the lug.

 

[marconi]

What is and also what was the supply for in the building?

 

[Electro-tech]

It is possible at some point that was DNO equipment judging by the bare earth and and the lug.

The bare earth & lug are from a previous old cable run with a resistance of 753 ohms the remains of the old cable are in the floor. Been in a few years. thanks for your input.

 

[Electro-tech]

What is and also what was the supply for in the building?

The supply is a 300A TP&N sub main feed to a Distribution panel to supply around 10 small business Units.

 

[marconi]

It may help others to advise if you could say where it is geographically.

I turned this up:

J. G. Statter and Co - Graces Guide

www.gracesguide.co.uk

I think this is one for Lucien Nunes to get his teeth into.