OP
Trulyshocking
Hi chaps.... sorry, been busy digging 
@ Mogga :- Yes, condensation is one of the reasons I'm reluctant to use the RCD, during early spring the inside of these columns becomes a wadi!! My current plan is to go for as highly rated an RCD as I can get away with.
@ Pjay :- Unfortunately, dont think this will be of any benefit in this situation..... The installation is pretty much a straight line, with the first post being just less than half way along it!
I should probably put the situation into context more for all you helpful chaps
The streetlighting installation is on an MOD airbase and is about 40 - 50 years old. It was originally wired in 16mm ish PILC which as mentioned is in death throws!! 16 years ago, contractors were asked to add another 16 posts to the circuits totaling about 25 in all. This circuit is fed from a feeder piller (32A BS88), through a contactor (which is part of the site blackout system for aircraft, which is operated remotely) and then out on 3 core SWA (2 live conductors (both same phase) and 1 Neutral, with sheath as cpc). This links up with the PILC at some point underground and feeds the 25 odd columns (12 to the west of the origin and 13 to the east, covering about 1/3 mile in each direction (yeah I know!!). The entire circuit looks a bit like an H with the origin in the middle. I have the test sheets from 16 years ago when the extra columns were added (on a minor works cert!) which show a Zs of nearly 40 ohms!!!!! Apparently this was acceptable?!?!?! I've spent an age trying to trace this cable with a Cat & Genny (no records/plans available!!) but due to the cable being run close to data, drainage and foul water, LV and mostly HV cabling, the first 4 exploratory digs have proved fruitless (or my cat and genny work is REALLY bad!!) Fridays dig has turned up the first underground T joint (to a post). I'm going to split this and test the main each side to see whats usable and whats not. Im not expecting any of it to be, and the digging is mainly to appease the bean counters who want me to use as much of the PILC as possible to keep costs down.
The part of the circuit I'm installing the new supply to, consists of 6 columns which were added beyond the extremity of the original circuit. I think it would seem obvious to most of us that it needs to be started from scratch, but the bean counters obviously want this done on the cheap (which is why we're in this trouble to begin with!!).
Hopefully this has put it into context a bit more, but basically I'm expecting to run supplies out from the contactor to power up various parts of the circuit, with lots of SWA run along walls and the minimum of trenches All I can do is make the best of yet another MOD 'bad job'!!
Cheers for the help so far.... TS
@ Mogga :- Yes, condensation is one of the reasons I'm reluctant to use the RCD, during early spring the inside of these columns becomes a wadi!! My current plan is to go for as highly rated an RCD as I can get away with.
@ Pjay :- Unfortunately, dont think this will be of any benefit in this situation..... The installation is pretty much a straight line, with the first post being just less than half way along it!
I should probably put the situation into context more for all you helpful chaps
The streetlighting installation is on an MOD airbase and is about 40 - 50 years old. It was originally wired in 16mm ish PILC which as mentioned is in death throws!! 16 years ago, contractors were asked to add another 16 posts to the circuits totaling about 25 in all. This circuit is fed from a feeder piller (32A BS88), through a contactor (which is part of the site blackout system for aircraft, which is operated remotely) and then out on 3 core SWA (2 live conductors (both same phase) and 1 Neutral, with sheath as cpc). This links up with the PILC at some point underground and feeds the 25 odd columns (12 to the west of the origin and 13 to the east, covering about 1/3 mile in each direction (yeah I know!!). The entire circuit looks a bit like an H with the origin in the middle. I have the test sheets from 16 years ago when the extra columns were added (on a minor works cert!) which show a Zs of nearly 40 ohms!!!!! Apparently this was acceptable?!?!?! I've spent an age trying to trace this cable with a Cat & Genny (no records/plans available!!) but due to the cable being run close to data, drainage and foul water, LV and mostly HV cabling, the first 4 exploratory digs have proved fruitless (or my cat and genny work is REALLY bad!!) Fridays dig has turned up the first underground T joint (to a post). I'm going to split this and test the main each side to see whats usable and whats not. Im not expecting any of it to be, and the digging is mainly to appease the bean counters who want me to use as much of the PILC as possible to keep costs down.
The part of the circuit I'm installing the new supply to, consists of 6 columns which were added beyond the extremity of the original circuit. I think it would seem obvious to most of us that it needs to be started from scratch, but the bean counters obviously want this done on the cheap (which is why we're in this trouble to begin with!!).
Hopefully this has put it into context a bit more, but basically I'm expecting to run supplies out from the contactor to power up various parts of the circuit, with lots of SWA run along walls and the minimum of trenches
All I can do is make the best of yet another MOD 'bad job'!!Cheers for the help so far.... TS
