Lamp fails to illuminate in spite of 239.5v at incoming supply

[silverserpent61]

Good morning all

I have a customer who had been having problems with some external lighting, on my initial visit I found that the main switch RCD was tripped and would not reset I carried out IR and continuity tests and found no fault but the circuit in question was protected additionally by an RCBO so I replaced that with an mcb & replaced the main switch RCD as this would not reset even with all circuits disconnected, at this time I noticed that the neutral connection from the main isolator to the neutral terminal was baldly fitted and had started to overheat so yesterday I replaced The ccu.

Now all other circuitS are working correctly, the exception being the external lighting to the front of the property. So I disconnected the the lighting circuit at the first point of utilisation found that I had 240v ish and no apparent faults so connected the first luminaire (an oldish metal bulkhead) and switch, switched on to test and nothing checked the wiring, lamp(S) and switch and all seem to be working fine tried many configurations all to no avail so dismantled and just rigged up a working bulb in a working lamp holder and connected directly to the supply cable and still no illumination!!!

 I am probably missing something obvious and will return this morning with a fresh head, if anybody has any BRIGHT ideas to illuminate me I shall be eternally Grateful.

regards, Craig...

 

[Murdoch]

I would do a Rn + R2 from the outside light back to the CU next

 

[silverserpent61]

I would do a Rn + R2 from the outside light back to the CU next

 Thank you for responding, That’s my first job when I arrive on site ! As it is about the only thing I didn’t do yesterday, But still can’t see why the thing will not illuminate 

 

[Murdoch]

BTW .... changing mcbs and adding upfront RCDs is no way to fault find unless it’s definitely contributing to the issue

 

[Geoff1946]

Sounds like a broken neutral to me. What are you checking the voltage with?

 

[silverserpent61]

BTW .... changing mcbs and adding upfront RCDs is no way to fault find unless it’s definitely contributing to the issue

Did not add just replaced like for like

Sounds like a broken neutral to me. What are you checking the voltage with?

Fluke multi function