PIR / RCD Problem

[mte29]

Hi, i have installed a PIR sensor for a hotel entrance, so that it rings a bell when someone triggers the sensor.

I have wired as follows: from consumer unit to PIR - neutral, live and earth - then from PIR neutral and L1 to Bell Transformer - then from transformer to bell.

When powered it is fine but as soon as the sensor is triggered the bell rings once and the RCD trips.

Any ideas?

 

[oharaf]

What did you get for continuity and IR?

 

[ericmark]

You will likely find the whole set-up draws only about 30ma so any fault it unlikely to trip an RCD until you draw full current.

What were the reading you got when making out insulation cert?

 

[mte29]

Continuity and Insulation Resistance were both fine. Run is fairly shot only about 35 meters in total so R1+R2 was low about 0.35 and all cable is new.

 

[oharaf]

Not being funny, have you terminated the neutral in the correct neutral bar?

 

[mte29]

Thats fine. Yes i have double checked that all line and neutrals are correct and they are.
It must be something to do with the switch (L1) live but can't seem to figure it out.

 

[oharaf]

Any chance that when the PIR switches it may be bring in an imbalance hence the RCD tripping? try a C type breaker and see if that removes the problem

 

[BS3036]

I'd guess (if its a real electric bell) that as this is a highly inductive circuit switching itself on and off, it is causing large spikes which can fool an RCD of a type with an electronic circuit.

It may be that the RCD in question is already close to tripping and is just pushed over the limit by these spikes. You could give the circuit its own RCBO, or you could add a snubber circuit to the feed to the bell to reduce the spikes.

 

[Taylortwocities]

Is this bell & its transformer totally dedicated to the PIR and powered from the same MCB or is it powered from somewhere else?