I've just fitted a new 17th edition (dual RCD) consumer unit in place of a very old BS3036 re-wireable fuse board. I encountered a problem when I split the upstairs and downstairs lights on to different RCD's (to ensure some lights stay on in the event of one RCD failure); When I turned on the upstairs landing light from either two way switch, both RCD's would trip. I initially thought I had a problem with the cable for the landing light that was being masked by the older less sensitive consumer unit. However, after a little thinking and further investigation I discovered that the landing light, although being supplied with the live/positive from the downstairs circuit, was picking up a neutral from the upstairs lighting circuit. Hence, when I turned on the lights there was an imbalance on both RCD search coils and both RCD's tripped. Basically the downstairs light RCD was supplying the current on the positive/live but this was not being returned on the relevant neutral and so an imbalance occurred on that RCD causing a trip. The upstairs lighting RCD was not supplying the current from the positive but was receiving it back on the neutral and hence an imbalance occurred and this RCD also tripped.
For now I have put both circuits on the same RCD until I get around to getting a neutral from the downstairs lighting circuit into the roof and can connect the landing light to this.
Hope this helps anyone who may experience a similar problem.
For now I have put both circuits on the same RCD until I get around to getting a neutral from the downstairs lighting circuit into the roof and can connect the landing light to this.
Hope this helps anyone who may experience a similar problem.
