extending the earthing arrangement for a steel framed commercial building under 18th edition

[cprfenom]

Hi Guys,

This is my situation:

Existing brick building demolished and replaced with steel frame, steel panel clad warehouse/storage structure.

Original building had two electrical supplies:
1 x 63A single phase and neutral via 3 core PVC SWA PVC
1 x 100A TPN via 4 core PVC SWA PVC plus equal csa CPC

Both supplies will be reinstated but only SPN used to feed LED lighting, small power, intruder/fire alarm supply and electric roller shutter.

Will be providing RCBO protection on final circuits but is there a get out clause for not providing RCD on alarm circuit?

Existing incoming main is approx. 60 years old comprising an 800A TPN cubicle panel fed from a 750kVA on site transformer.
Cubicle is fitted with BS88 fuse protection to sub main cables feeding various distribution boards throughout the building.

Surge protection class 1/2 will be installed in the new building, but not sure if the client wants to install lightning protection.

I guess my question is to TT or extend the existing TN-S?

 

[Ian1981]

If there’s no lightning protection then why do you want to install a type 1 spd?
Type 1 are installed to work with the LPS as type 2 do not protect against lightning overvoltages.

If you can then use the existing TN-S you then can avoid rcd protection to any circuits that do not require it.

 

[MFS Electrical]

Not really much need in not using an RCD on the alarm circuit as it will have battery backup anyway?

 

[cprfenom]

I don't know why I put that. A mistake lol

 

[Strima]

Depending on the cable run the alarm circuit may not require RCD protection. Unless you're connecting it using a three pin plug...

 

[magnoliafan89]

If there’s no lightning protection then why do you want to install a type 1 spd?
Type 1 are installed to work with the LPS as type 2 do not protect against lightning overvoltages.

If you can then use the existing TN-S you then can avoid rcd protection to any circuits that do not require it.

What does lps stand for?

 

[Ian1981]

What does lps stand for?

Lightning protection system

 

[cprfenom]

I would be installing a 1/2 surge as it is not known yet if the client will install an LPS. The building is over shadowed by local buildings and I wonder if it is actually required.

This is not something I am qualified to comment on.

 

[bigspark17]

Happy to be corrected if wrong but doesn't a bs5839 part 1 power supply prohibit use of a rcd on its supply?

 

[Ian1981]

Happy to be corrected if wrong but doesn't a bs5839 part 1 power supply prohibit use of a rcd on its supply?

No as with TT systems it sometimes can’t be avoided and the circuit would require earth fault protection by say a 100mA rcd but 30mA if additional protection is required for the cable buried in the wall without mechanical protection, earthed conduit etc.

 

[Ian1981]

Happy to be corrected if wrong but doesn't a bs5839 part 1 power supply prohibit use of a rcd on its supply?

Then prove me wrong as simply disagreeing is pointless
It should ideally not be rcd protected but if for safety reasons it has to be, as with a TT system and rcd protection is required for earth fault protection but ,if you bother to look it up it is not prohibited!