Identifying the system

[Michael Davis-McCoy]

Hi all, I'm trying to identify a supply. Visually the supply looks like a TNS. An earth clamp is around the metal sheath of the incoming supply cable to an earth terminal block. Three phases and neutral out of the Henley unit. When I was carrying out a loop test Line and Neutral at the distribution board, my Megger LT5 lights up as Line and Earth. Telling me it's a TNCS. My tester works properly as I tested it on a commercial DB the day before. Both line and neutral, line and earth.
The whole thing is suspect as I noticed a few errors and incorrect information throughout the main room.
Any help would be appreciated.

Thank you

 

[markythesparky]

Why are you doing an earth loop test to neutral?

Even if the system is TN-S the earth will be connected back at the substation.

 

[Toneyz]

A photo would be good so that we could come to the same conclusion. You may be getting the same readings due to another supply nearby as TNC-S.

 

[Michael Davis-McCoy]

The loop test Line to Neutral is for the PSC.
The loop test Line to Earth is the PFC.
I am putting the design calculations together for the job it's self.

 

[Michael Davis-McCoy]

Found the solution, it was on old LT5 instructions, a note on it says when loop testing Line and Neutral, the Line and Earth neon illuminates , not the expected Line and Neutral as you would have thought. I won't forget that one. Had to search the internet for that one.
I bought the loop tester last week. I used them 25 years ago. They are great for boards, lights, checking pipe work. I have a Robin multi tester and loop/PFC tester.
The system is a TNS.
I'm making sure I have the design criteria for and job I do, using The BBB.