Problem with 2 way landing whilst replace consumer unit

[bodge64]

I have just fitted a Dual RCD split board consumer unit to an existing installation. I wired the upstairs lights to one side and the downstairs lights to the other but when the landing light was switched on the RCD tripped so I looked inside the switches and the feed to the downstairs switch was shared with a hall light.I suspected an imbalance triggering the RCD. I then connected both upstairs and downstairs to the same RCD but had the same problem ,also with the other RCD. Does anyone have any suggestions please?

 

[PC Electrics]

Have you checked for the usual 'shared neutral' scenario?

 

[tony mc]

Were all your dead tests good on the ccts ??

 

[High Tower]

gotta be a borrowed neutral!

 

[Sintra]

Borrowed neutral is the norm in these scenarios.

 

[i=p/u]

neutral could be chopped, dont take my word, but is this possible sinatra and co.

 

[Des 56]

I then connected both upstairs and downstairs to the same RCD but had the same problem ,also with the other RCD.

Very unlikely and i shouldn't really ask this, but you haven't gone and had one of those blonde moments we all get time to time , and moved the lives on to the same rcd and forgot the neutrals and left them seperate

 

[bodge64]

thanks everyone! If I chase a neutral from another upstairs light should this do the trick? Not to familiar with domestic installations but more industrial!

 

[i=p/u]

can be done but make sure you leave loads of notes and circuit chart saying this situation.. think would be best

 

[sparky05084]

I agree with Des 56. It is quite possible that you have either A) got your Neutrals mixed up between the split load bars or B) your Neutrals are correct and it is the Line conductors that are infact mixed up. This would seem to be pointing in the right direction I think as you mentioned that putting them together on both RCD’s respectively did not rectify the problem. This is an easy mistake to make and I know this speaking from experience.
Can I ask were or are the cable conductors easily traceable in the consumer unit and did you definitely identify the ends? I say this because sometimes what you think is Neutral or a Line of a cable may turn out to be one of another (especially if cables are compacted and tight and come through same hole).
I hope this makes sense. Even I got confused for a minute
I work for a housing association on voids and I find a lot of the time the "borrowed Neutral" setup where by there is usually a 2 gang switch in the downstairs hallway, one for the hall light and one obviously does the landing light. It is wired in what us lads call the "Cheshire Two Way" set up where the feed is looped from the common of the hall light over to the common of the 2 way and then a 2 core twin is sent to the upstairs landing light and thus a single core (Red) to the landing light.
As a rule of thumb and to keep within our spec we have to rewire it and pull in a new 3 core cable and a new twin to the light. Bit of a pin but I prefer this than running a new neutral between the upstairs and downstairs light.
Does the above sound like what you have?

 

[bodge64]

I did ident all the conductors before disconecting the old fusebox, but as you described as " the cheshire 2 way" is exactly whats been done. I am doing the job as a favour for my wifes aunt and uncle, what would be the least disruptive way to rectify this?

 

[sparky05084]

Ok. I don't want to sound like I'm telling you how to suck eggs here but as a rule of thumb it is always wise to identify your conductor ends to make sure you know exactly what is what and I don't necessarily mean when you remove the old consumer unit but when you go to place the new one on.

Assuming that you have identified that your Line conductors and Neutrals are corresponding and are not mixed up/swapped between MCB's or Neutral bars then I would suggest that you run a separate Neutral from the Hallway to the landing light. To avoid nuisance tripping, at the landing light the Neutrals are put into a connector block, taped up and tucked into loft space. The new twin and cpc that you have run in goes into neutral connection. Not best practice I believe and will no doubt raise eyebrows to sparks reading this.
Please correct me guys if I'm talking rubbish.

As for minimizing mess, well that depends on the route you choose to take. Is there an airing cupboard on landing or some where you can put trunking up without it bothering customer?

I think that I have this right but I'm pretty sure in your initial post you don't actually mention if it's between the hall and landing light.

 

[TPES]

You say you've moved both lighting circuits to the same RCD side of the board... But have you moved both neutrals over to the same bar? Double check and be sure, no other reason while the RCD should trip when a switch is pressed.. If it does then I would do IR tests..

 

[bodge64]

Did IR test on all circuits before installing but will check Neutrals when i go up tomorrow. I don't know how you guys do domestic work all the time, it would drive me nuts!

 

[sparky05084]

Good luck hope you get it sorted. Give us a shout when you know what it was. Oh and for the record, yes domestic does drive you a bit batty, especially in empty properties day in and day out