Board change

Good grief, the new work is the DB change. The final circuits are not new.

Sorry, I'm sure we're getting at cross purposes here...


I'm not trying to suggest that the final circuits are new - quite the contrary. The point I'm trying to make is that the new work does include the first 6 inches (say) of the existing final circuit cabling - where the cables have been removed from the old CU, wiggled about all over the place and re-terminated into the new CU. There is a possibility of introducing faults into the existing circuits during that process - whether it be loosing earthing due to a bad connection to the earth bar (screw biting down on the sleeving rather than the conductor) or the old wires snapping off inside the sleeving, insulation being damaged (or existing unnoticed damage now resulting in an actual fault against the new metal CU case) or even reverse polarity (perhaps where connected to an RCBO) - so the new I&T needs to somehow show (AFARP) that such faults haven't been introduced.


I'll admit that situation might be confused by the current fashion of dead testing final circuits while they're disconnected from the CU (e.g. by choc blocking L and PE together for a R1+R2 test thus not checking what's probably the most critical single connection - rather than linking L to the earth bar) - at least the 17th onwards insists that insulation tests be done with the c.p.c.s connected to earth. Not helped of course by some RCDs having to be disconnected during insulation tests, nor the lack of emphasis of 'overall' tests on the completed CU (despite the wording of the actual regulations). I'm sure the switch to metal CUs will catch out a number of situations that whet unnoticed with the old insulating CUs.


So I'm not saying you need to do a full set of tests over the entire existing final circuits - but some testing will be needed. Perhaps a loop test at the first convenient point on each outgoing circuit (to check earth continuity & polarity) - perhaps preceded by a R1 continuity check if you think there's any risk of a live loop test posing a hazard if the c.p.c. wasn't intact.  An insulation test certainly - even if it's just a global L+N to PE test on the completed board.


  - Andy.

Good grief, the new work is the DB change. The final circuits are not new.

Sorry, I'm sure we're getting at cross purposes here...


I'm not trying to suggest that the final circuits are new - quite the contrary. The point I'm trying to make is that the new work does include the first 6 inches (say) of the existing final circuit cabling - where the cables have been removed from the old CU, wiggled about all over the place and re-terminated into the new CU. There is a possibility of introducing faults into the existing circuits during that process - whether it be loosing earthing due to a bad connection to the earth bar (screw biting down on the sleeving rather than the conductor) or the old wires snapping off inside the sleeving, insulation being damaged (or existing unnoticed damage now resulting in an actual fault against the new metal CU case) or even reverse polarity (perhaps where connected to an RCBO) - so the new I&T needs to somehow show (AFARP) that such faults haven't been introduced.


I'll admit that situation might be confused by the current fashion of dead testing final circuits while they're disconnected from the CU (e.g. by choc blocking L and PE together for a R1+R2 test thus not checking what's probably the most critical single connection - rather than linking L to the earth bar) - at least the 17th onwards insists that insulation tests be done with the c.p.c.s connected to earth. Not helped of course by some RCDs having to be disconnected during insulation tests, nor the lack of emphasis of 'overall' tests on the completed CU (despite the wording of the actual regulations). I'm sure the switch to metal CUs will catch out a number of situations that whet unnoticed with the old insulating CUs.


So I'm not saying you need to do a full set of tests over the entire existing final circuits - but some testing will be needed. Perhaps a loop test at the first convenient point on each outgoing circuit (to check earth continuity & polarity) - perhaps preceded by a R1 continuity check if you think there's any risk of a live loop test posing a hazard if the c.p.c. wasn't intact.  An insulation test certainly - even if it's just a global L+N to PE test on the completed board.


  - Andy.