LightwaveRF 2 way tripping RCD

[78andyp]

I have installed some generation 2 LightwaveRF units.
I have replaced a 3 gang switch downstairs with a new Gen 2 3 gang switch (just released) - one of the gangs is a 2 way landing light.
I've also replaced the upstairs landing switch with a Gen 2 1 gang switch.
Note that Gen 2 units aren't master and slave like Gen 1 units - that's done in software.

The original wiring can be seen in the photos.
Upstairs:
Switched live (black) and 3 core blue to L1
3 core yellow to COM
Live (red) and 3 core red to L2
(Note this seems somewhat different from most standard wiring diagrams)

Downstairs: (the left most gang)
3 core red to L1
3 core yellow to COM
3 core blue to L2

Following the lightwave instructions here (https://support.lightwaverf.com/hc/...tion_2__2_way_with_one_intermediate_point.pdf) I have done the following:

Upstairs: (now 1 gang gen 2 lightwave rf unit)
Live (red) to 'L'
Switched live (back) AND 3 core yellow to 'X/switched'
3 core red and blue capped

Downstairs:
3 core yellow to 'X/switched'
3 core red and blue capped
NB - the whole 3 gang unit only takes ONE live input - this powers all 3 gangs. This is from one of the downstairs lights (the other two gangs are 1 way porch and hall).
(See https://support.lightwaverf.com/hc/en-us/articles/115001530231-Lighting-guides-Generation-2- for the manuals)

Result:
The upstairs light switch works fine
The downstairs light switch trips the RCD

WHY??
Is it because the power is effectively coming from the downstairs circuit yet the switched live feeds an upstairs light - does this create a imbalance the RCD senses??
If so what can I do about it - as, unlike the 2 gang gen 2 unit which has one live input for each gang, the 3 gang only has one - and if I was to use one of the other 3 core wires to take a live from upstairs presumably then the two downstairs switches would trip.

Grateful for thoughts.
Thanks
Andy

 

[ban-all-sheds]

With the disclaimer that I have not read your post in great detail, I'd say that "Why?" is because your lighting circuits are on different RCDs, and that therefore something where "the whole 3 gang unit only takes ONE live input" is incompatible.

You'll have to use separate Lightwave switches.

 

[ban-all-sheds]

OOI, what problems were you having operating conventional switches which meant you had to install this system?

 

[winston1]

It's the common borrowed neutral problem with 2 way hall landing switches, except in this case it is a borrowed line.

 

[Taylortwocities]

You'll have to use separate Lightwave switches.

You could put Both lighting circuits on one RCD (still with separate MCBs) But that does mean that the whole house goes dark if/when the RCD trips.

 

[78andyp]

Thanks all.

Quick update - I disconnected and capped the yellow wire in the upstairs switch - so now there is no physical connection between both switches and they still work - ie. the downstairs switch is all done in software.

@ban-all-sheds - no problems per se!
1) I'm a geek and playing with home automation
2) Often out of the house a lot and can program lights to come on and off
3) Similarly can automate lights to turn off when leave home in case I leave them on!
4) The dimming is actually useful in the kids rooms for bedtimes

@winston1 - Thanks. I had found some info about borrowed neutral.

@Taylortwocities - Thanks. I suspect that would work but it is well beyond my skills. It is the RCD that trips not the MCBs.

 

[ban-all-sheds]

You could put Both lighting circuits on one RCD (still with separate MCBs) But that does mean that the whole house goes dark if/when the RCD trips.

I dismissed that option as a clear contravention of the Wiring Regulations, and an actual criminal offence under the Building Regulations.

 

[Taylortwocities]

@Taylortwocities - Thanks. I suspect that would work but it is well beyond my skills. It is the RCD that trips not the MCBs.

I know it’s the RCD that trips. My solution would solve that issue. Post a photo of your consumer unit and I can explain more.

But it looks like I’m called to room 101 for even thinking to suggest a workable solution.

I dismissed that option as a clear contravention of the Wiring Regulations, and an actual criminal offence under the Building Regulations.

Yes, call a policeman.

 

[78andyp]

You could put Both lighting circuits on one RCD (still with separate MCBs) But that does mean that the whole house goes dark if/when the RCD trips.

I know it’s the RCD that trips. My solution would solve that issue. Post a photo of your consumer unit and I can explain more.

Hi
Picture attached.
@ban-all-sheds - I clearly have no knowledge here but from my reading I understood that having upstairs light (+downstairs plugs) and downstairs lights (+upstairs plugs) on separate RCDs was more custom and practice to spread the load (esp. when bulbs weren't energy saving as they are now) rather than law.... obviously I am wrong??
Thank you both,
Andy

 

[Taylortwocities]

Your CU is in two halves. Each half is protected by a separate RCD.
You have the upstairs lighting on one half and the downstairs on the other RCD. This is the normal way of doing things, as it means that, should something trip, you don't lose the lights for the whole house.
As you have essentially combined the up and downstairs lights in your fancy switch, the RCD sees it as a fault and trips. It is doing its job.

A quick and dirty way of fixing your issue would have been to move the upstairs lighting MCB on to the other side of the CU so that all the lighting is on one RCD. This would have solved your tripping issue, but you can't easily do that as your bargain basement consumer unit (Chint, ugh) has no spare spaces. It can be done, but it would need some serious re-engineering of the consumer unit.

Another solution is needed. As BAS suggested, maybe

You'll have to use separate Lightwave switches.

Or put the old switches back. Or rewire the lighting circuits in your house to suit your new switches.

Isn't technology wonderful?

 

[78andyp]

Hi
Thanks. As I said it does actually work wirelessly.
BUT - out of academic curiosity....
On the left side of the CU - I don't actually have an immersion heater any more (I think this is the boiler now though), and I don't have an electric shower - so I think the shower one is free.
Are you suggesting I could move the other light MCB into that slot??
Cheers
Andy

 

[Taylortwocities]

As you are already in the poo, with electrical things, and as you have already admitted

it is well beyond my skills.

I think that re-engineering a consumer unit is outside your skill set.
You need an electrician to do that. There are a few gotchas to think about.

 

[78andyp]

As you are already in the poo, with electrical things, and as you have already admitted
I think that re-engineering a consumer unit is outside your skill set.
You need an electrician to do that. There are a few gotchas to think about.

I wouldn't say I was 'in the poo'. I have a solution that works, and if it didn't it is within in my skillset to put the switches I took off back on (although I did have to change the back box from a single to a double but that just means buying a new faceplate!).
But yes I agree fully, rewiring a CU is beyond anything I have done before... although in fairness it was your suggestion that took us down this route..

I know it’s the RCD that trips. My solution would solve that issue. Post a photo of your consumer unit and I can explain more.

I am happy to leave things as they are. Thank you for all your help.
Andy

 

[ban-all-sheds]

I clearly have no knowledge here but from my reading I understood that having upstairs light (+downstairs plugs) and downstairs lights (+upstairs plugs) on separate RCDs was more custom and practice to spread the load (esp. when bulbs weren't energy saving as they are now) rather than law.... obviously I am wrong??

The Wiring Regulations require that

314.1   Every installation shall be divided into circuits, as necessary, to:
(i) avoid danger and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Chapter 46 and Section 537)
(iii) take account of hazards that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor (PE) currents not due to a fault
(v) mitigate the effects of electromagnetic disturbances (see also Chapter 44)
(vi) prevent the indirect energizing of a circuit intended to be isolated.​

To take an installation where the lighting circuits are on different RCDs and change it so that they are on the same one must surely be a contravention. The Building Regulations make it an offence to make a controlled service (which the electrical installation is) less satisfactory than it was before.

Putting fatuous comments about calling a policeman to one side, it is simply not a solution which people should be advising.