Light switch setting off alarm

[Kyran O'Regan]

Hi, I just installed a new light switch in my downstairs bathroom which is near the house alarm. It is a 2 gang 2 way switch with the other switch directly beside the alarm. The new switch controls the bathroom light and extractor fan, and there is a lot of "buzzing" in the bathroom when the light is turned on and off, but this has always been the case. The problem is that often, when I switch the bathroom light on, the alarm starts to beep, and it shows that the mains power supply has been shut off so any insights into this would be greatly appreciated. Thanks

 

[JohnD]

What make and model?

Is it wireless?

photos may help.

 

[Kyran O'Regan]

I think the alarm is an Aritech CD 3403. Its been there since the house was built about 20 years ago and it's all wired. There is also an Aritech box in the bathroom where the issue with the light is and a buzzing sound does come from that box.

 

[The Pars]

So when you switch the light on the power to the alarm panel goes off?
Power for the panel has been taken of the switch and wired wrong.
I would suggest you need an engineer/sparky to have a look at this.
I don’t like the sound of something electrical buzzing

 

[bernardgreen]

I wonder if the supply Live and Neutral to the alarm have been connected incorrectly in the switch

It should be
Alarm Live to Permanent Live in the switch
Alarm Neutral to Neutral in the switch

BUT

there may not be a Neutral in the switch and what has been wired is

Alarm Live to Permanent Live in the switch ( correct )

Alarm Neutral to a Blue ( or Black ) which was though to be a Neutral because it was Blue ( or Black ) ( incorrect )

The Blue ( or Black ) is the Switched Live to the lamp. A common DIY error is to assume a Blue ( or Black ) wire is always Neutral

With the switch OFF the Blue ( or Black ) can supply a pseudo Neutral via the lamp. The alarm and lamp are connected in series and the alarm will get some power. The lamp may be glowing very slightly with the current flowing through it from Neutral to the alarm.

With the switch ON the Switched Live is connected to Permanent Live effectively shorting the supply to the alarm and connecting Live to the lamp.

 

[The Pars]

Plus there should be a 3amp in switched fused spur installed so you can turn the supply off to the alarm panel safely.
I have never wired of a light supply.

 

[Kyran O'Regan]

ThanksI got there eventually. I had the wire for the alarms power connected to one of the line terminals for the light...