Question from 2330 Level 3 book

[Martin.h.lee]

This is a sample question.

"You have been asked by your employer to investigate an 'earthing' problem that has been reported by a customer. The customer concerned has just moved into a large 80-year old house that will allow him to work from home as a computer software designer. The house has large gardens, a seperate garage, three outside security lights and a gas-fired contral-heating system. The customer will be working from one of the bedrooms on his computers.

The customer has reported that he is getting intermittent RCD trips on the main consumer unit. The customer has noticed that the trips seem to occur only at night and only when it has been raining. Rain during the day does not cause the same problems. There is also a circuit out to the garage that has its own RCD and this does not trip.

What do you think could be causing the problem?"

This question is given by Heinemann book for 2330 level 3. (p.307)
What can be an answer?
I guess some earth fault of the circuit due to the raining. However I don't understand why the problem occurs only at night.

Thanks

 

[Silly Sausage]

The answer is in the first paragraph.
Have a careful read and you'll see it!!!

 

[a1guvner]

i would take a stab at the external security lights, it could be dusk till dawn sensor which could eliminate the tripping during the day if there was water ingress on the load side of the sensor

 

[telectrix]

or a PIR sensor stopping the lights from activating in daytime. definitely sounds like water in security light/s.