Discuss Three Phase overhead supply is it TN C in the Periodic Inspection Reporting & Certification area at ElectriciansForums.net

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While carrying out a EICR I found on first inspection that there were no RCDs installed . When I checked at the Pole Mounted Transformer the Earth & Neutral were connected at the Neutral point. So am I right in concluding it's a TN-C System? The 17th Edition states that RCDs should not be installed where a TN C System is used (411.4.4)
 
I will take a pic tomorrow,but it looks like the Earth and Neutral are connected at the transfer. The reason I am suspecting is a TN-C is the lack of RCD protection on the Ring main final circuits. If it was a TT it would be protected with RCD at the mains
 
Yes, or any final circuit in the building, by the way it feeds a hotel. The overhead feed is by way of bundle conductors (4) sorry that's a South African term. I don't know what you call them here?
 

Eh?
The 17th Edition states that RCDs should not be installed where a TN C System is used 411.4.4

The following types of protective device may be used for fault protection:
(i) An overcurrent protective device
(ii) An RCD.

It'll be a PME supply. Concentric cable split at the installation intake, to N & E.
 
Eh?
The 17th Edition states that RCDs should not be installed where a TN C System is used 411.4.4

The following types of protective device may be used for fault protection:
(i) An overcurrent protective device
(ii) An RCD.

It'll be a PME supply. Concentric cable split at the installation intake, to N & E.

Read on a couple of lines after Note 1
"An RCD Shat be used in a TN-C system"
 
That'll be 414.4.5 for no RCD on TN-C?
 
I think you might be getting confused here chief, TNC is NOT allowed within an installation. TNC/PME supply, then the Earth is split off at the intake.
Thanks, I will take a closer look at the intake, I just don't understand why there are no RCDs on the final ring circuits this hotel has 6 DBs
 
My house has a two wire supply coming in along the outside wall, it was clearly a TT in the past but has been converted to TNC even though the supply is via 2 individual separate single cores.
The DNO risk access any existing TT before conversion I am led to believe, I see no reason why your install won't have been converted at some point even an overhead supply.
 
You probably have TN-C external to the building then the PEN conductor is separated at the service head which gives the S on TN-C-S.
 

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