Smart Light Switch - What am I missing?

[C70R]

I'm in the process of installing a load of smart home stuff in our new house, and wanted to put a simple smart light switch in place of a single gang switch to control a series of kitchen spots.

Knowing that this part of the house was more modern (2000s extension), I gambled that there was a neutral wire. I bought this switch, which has good reviews. https://www.amazon.co.uk/dp/B07WFKJ27C

Upon removing the old switch I found two blue neutral wires joined together behind, a brown live into the COM slot and a brown live into L1. Great.

I installed both neutral wires into the neutral slot on the smart socket, L1 into L1 and COM into L, per the manual. There was no other way to wire it I could see.

Turning the circuit breaker back on caused my RCD to trip. I tried again, and the switch had powered up (with the lights off), but pressing the physical button tripped the RCD again. Reinstalling the old switch has everything working fine again.

I'm confused. I've swapped sockets and switches before, so I'm no idiot. I wired it per the instructions, so it should have worked.

Did I do something wrong?
Faulty smart switch?
Something else?

Answers on a postcard...

Edited by C70R on Thursday 13th October 10:02

[Baldchap]

Picture 3 says it cannot be used as a 2 way switch.

[OutInTheShed]

I'm guessing your old dumb switch had its 'COM' termnial connected to the load and L1 to the source?

[C70R]

OutInTheShed said:

I'm guessing your old dumb switch had its 'COM' termnial connected to the load and L1 to the source?

You mean the Live wires were connected the wrong way around in the old switch? I hadn't even considered that. However, the new smart switch wouldn't have even powered up if I got those the wrong way around, would it?

I did a bit of poking with a multimeter to try and establish which circuit had the bulbs on it, but couldn't work it out.

[C70R]

Baldchap said:

Picture 3 says it cannot be used as a 2 way switch.

It wasn't being used as a two-way switch. This is the only switch that controls these lights.

[LordLoveLength]

Is the neutral connection at the board correct? Connected to the right bus bar associated with the phase for the light? Or is it borrowed from another circuit?

Is there an earth connection to the smart switch? Is it isolated from the neutral?

Could just be a faulty switch if the above checks out.

[C70R]

LordLoveLength said:

Is the neutral connection at the board correct? Connected to the right bus bar associated with the phase for the light? Or is it borrowed from another circuit?

Is there an earth connection to the smart switch? Is it isolated from the neutral?

Could just be a faulty switch if the above checks out.

I haven't checked the connection at the board, but the house was rewired as part of a recent-ish renovation, and appears to have been done to a high standard. I'll check.

The switch doesn't need an earth.

[ruggedscotty]

C70R said:

I'm in the process of installing a load of smart home stuff in our new house, and wanted to put a simple smart light switch in place of a single gang switch to control a series of kitchen spots.

Knowing that this part of the house was more modern (2000s extension), I gambled that there was a neutral wire. I bought this switch, which has good reviews. https://www.amazon.co.uk/dp/B07WFKJ27C

Upon removing the old switch I found two blue neutral wires joined together behind, a brown live into the COM slot and a brown live into L1. Great.

I installed both neutral wires into the neutral slot on the smart socket, L1 into L1 and COM into L, per the manual. There was no other way to wire it I could see.

Turning the circuit breaker back on caused my RCD to trip. I tried again, and the switch had powered up (with the lights off), but pressing the physical button tripped the RCD again. Reinstalling the old switch has everything working fine again.

I'm confused. I've swapped sockets and switches before, so I'm no idiot. I wired it per the instructions, so it should have worked.

Did I do something wrong?
Faulty smart switch?
Something else?

Answers on a postcard...

Edited by C70R on Thursday 13th October 10:02

assumptions with electricity is always a bad move.....

you should be looking to identify the colours behind the switch - house wiring is notorious for different colours being used...

Tripping the RCD means that something is generating an earth leakage.... or is that RCD tripping an RCBO and its not actually the RCD but a short thats tripping it....

Photos of the board and photos of behind the switch - give us all the facts....

[C70R]

ruggedscotty said:

assumptions with electricity is always a bad move.....

you should be looking to identify the colours behind the switch - house wiring is notorious for different colours being used...

Tripping the RCD means that something is generating an earth leakage.... or is that RCD tripping an RCBO and its not actually the RCD but a short thats tripping it....

Photos of the board and photos of behind the switch - give us all the facts....

Fair one. Evaluating the board goes a little beyond my abilities/knowledge, sadly. It seemed relatively straightforward, which is why I was happy to take it on.

Behind the switch there were two blue wires joined together (not connected to the dumb switch), so I'd say a safe assumption that this was the neutral ring.

I then had a brown wire going into the COM and a brown going into L1 on the dumb switch. Again, it seemed logical (because the dumb switch was working as intended) that these were my lives.

There's an earth connected in the back of the wall box, but neither switch requires it to be connected.

What I can't get my head around is why the smart switch powered up in 'off' mode, then tripped the RCD when switched to 'on'.
Surely if it was wired wrongly it would have tripped before it was switched to the 'on' position?

Edited by C70R on Friday 14th October 08:43

[OutInTheShed]

C70R said:

Fair one. Evaluating the board goes a little beyond my abilities/knowledge, sadly. It seemed relatively straightforward, which is why I was happy to take it on.

Behind the switch there were two blue wires joined together (not connected to the dumb switch), so I'd say a safe assumption that this was the neutral ring.

I then had a brown wire going into the COM and a brown going into L1 on the dumb switch. Again, it seemed logical (because the dumb switch was working as intended) that these were my lives.

There's an earth connected in the back of the wall box, but neither switch requires it to be connected.

What I can't get my head around is why the smart switch powered up in 'off' mode, then tripped the RCD when switched to 'on'.
Surely if it was wired wrongly it would have tripped before it was switched to the 'on' position?

Edited by C70R on Friday 14th October 08:43

Your 'load' wire shorting, or even leaking, to the earthed metal box would explain all.

IThe wires may be stressed in a shallow box with more than a basic switch and some fault makes itself known.

Been there!

[C70R]

OutInTheShed said:

C70R said:

Fair one. Evaluating the board goes a little beyond my abilities/knowledge, sadly. It seemed relatively straightforward, which is why I was happy to take it on.

Behind the switch there were two blue wires joined together (not connected to the dumb switch), so I'd say a safe assumption that this was the neutral ring.

I then had a brown wire going into the COM and a brown going into L1 on the dumb switch. Again, it seemed logical (because the dumb switch was working as intended) that these were my lives.

There's an earth connected in the back of the wall box, but neither switch requires it to be connected.

What I can't get my head around is why the smart switch powered up in 'off' mode, then tripped the RCD when switched to 'on'.
Surely if it was wired wrongly it would have tripped before it was switched to the 'on' position?

Edited by C70R on Friday 14th October 08:43

Your 'load' wire shorting, or even leaking, to the earthed metal box would explain all.

IThe wires may be stressed in a shallow box with more than a basic switch and some fault makes itself known.

Been there!

This is so simple, but you might have nailed it. I'll try the switch again without it screwed into the wall box this time.

It's a relatively deep box, but the switch is quite chunky.

Having said that, do you think it would only trip under load, when the switch is turned on (rather than when the circuit is live, and the switch is off)?

[C70R]

Switch spacer ordered, and due tomorrow. Will report back.

Is there an existing thread for smart home discussion?

Sort of a "Hey, has anyone tried this?" Or "Why isn't this thing working?" Or "How can I solve this problem with tech?"

[C70R]

C70R said:

This is so simple, but you might have nailed it. I'll try the switch again without it screwed into the wall box this time.

It's a relatively deep box, but the switch is quite chunky.

Having said that, do you think it would only trip under load, when the switch is turned on (rather than when the circuit is live, and the switch is off)?

Just asking this again.

[C70R]

OutInTheShed said:

Your 'load' wire shorting, or even leaking, to the earthed metal box would explain all.

IThe wires may be stressed in a shallow box with more than a basic switch and some fault makes itself known.

Been there!

My hero.

The switch works fine without screwing into the box, so I had a little dig around and spotted a neutral wire with a bit of broken insulation. It looks like this was sitting against the back of the switch, and likely shorting against the L1 terminal when the switch was activated.

Going to do a bit of judicious insulation on it and the earths (the box looks a bit slapdash on closer viewing), and fit the switch back in with the spacer. Annoyingly the spacer is a really bad fit, so I'm going to have to get another one anyway. But it will do for the foreseeable.

[C70R]

Sorted, and working perfectly.

Thank you so much!