This little just job.

[SUNRAY]

All electric including NSH rental 5 bed house, multiple C1, C2 & C3 on EICR in January. I can't tell whether they were justified as all of the work has been repaired by the inspector, including 2 Schneider all AFDD RCBO CU' with surge protection. Maybe 30 pieces of paper left for customer and he has done a really nice looking job including replacing ALL of the tails and adding isolator between meter and Henley (according to tenant they were all grey, now brown & blue).

Total of 8* 16 & 20A socket circuits (EICR showed 4* 32A ring) & 9* 16 & 20A NSH circuits.
The story is; ever since the repairs the utility room radial (including freezer) trips during the night, they think about 1-2am and the heating is not getting properly hot. Original electrician has been out a number of times, keeps giving it a clean bill of health and blaming white goods.
Managing agent asked my boss to help, he has sent one of the guys out who couldn't do much testing during the day.

My plan was simple; bypass the E7 contactor to start up the heaters while I looked at the white goods.
My first test, before doing anything else, with neon screwdriver (using as a voltstick) showed the phase tail between contactor and CU to be live. In fact the whole heating CU really was live.

Cutting this short I found the utility 16A radial had a 13A SFCU on the other side of the wall as the 24hr supply to the NSH, the 2 cables (24hr & cheaprate) were terminated into the same terminals inside the heater. This resulted in back feeding the 20A DP switch/20A RCBO cheaprate circuit to the heating CU, turning off either of those RCBO's depowered the heating CU.
Rewiring the NSH as it should be appeared to cure the problem, however that left a 3.3KW NSH, 2.7 KW tumble drier and freezer on a 16A RCBO, the second (20A RCBO) fed the WM & dishwasher and both circuits included a DSSO. I didn't like it but boss said to leave as is.

I did final testing and packed up, said my final goodbyes and left, sitting at home writing the report the thought struck me...

WHY did it only trip during the night? Followed by They also said the heating wasn't working properly.

I returned and inspected the E7 arrangement. This installation has a small {25/30A?} Teleswitch, I found the blue meter control wire was correct but the brown switch wire was in neutral in the Henley so the contactor couldn't operate.

It really didn't take much to discover the CU was live during the day.

 

[Taylortwocities]

My hero!

 

[SUNRAY]

My hero!

I'm far from feeling like a hero, more disgust/embarrassment that 2 others didn't see that the off peak CU had power on it during the day and one of those has had several return visits.
There is of course the possibility there is a RCD tripping issue but I predict it's off peak heaters overloading the 16A RCBO.

 

[securespark]

But that would be an overload issue, not a residual current issue.

 

[SUNRAY]

But that would be an overload issue, not a residual current issue.

Yes correct but at this point I know not if the RCBO tripped on overload or residual current. I'm fairly sure it's overload as the off peak contactor was not energised after the rewire. However bearing in mind the contactor only switches the phase, it means the neutrals of the 2 RCBO's are linked both sides so I'd be comfortable with either of them tripping in RCD mode at any time of the day, in fact thinking about it further they should have tripped.

I've heard this morning the NSH's are now heating correctly and nothing tripped since my visit nearly a week ago is now.

Apparently our fees are being deducted from the original contractors payment (which has been withheld) but of course that's nothing to do with me.