I have been checking the voltage on at my landing light as it keeps blowing bulbs. With the landing light switch turned off I get a reading of 106volts!! If the switch is turned on I get 247volts Likewise when I turn on the landing light using the downstairs switch. Can any one help me with this problem?
Firstly how are you measuring the voltage? Is the bulb still in circuit when you make the measurement?
My guess is that your landing light has a low energy CF bulb fitted and you are measuing with a high impedance multimeter. Landing lights are normally two-way switched which leaves a long run where one of the Switched-Live legs is live (but not connected to the lamp) alongside the other which not live but is connected to the lamp. Voltage is induced into the not-live leg. With an incandesant bulb this is then disipated to neutral but with a CF bulb it is not and builds up across the input capacitor so you measure a significant voltage. There's no real energy behind it though so don't worry.
Try taking the measurement again with a normal bulb fitted.
[BTW it is often the case that in this type of situation CF bulbs will give a low energy flash say once every 3 or so seconds as enough voltage accumulates for them to try to strike. It's very dim though so you might need to get up in the night to see it. It might also only happen with the switches in one off orientation but not the other.]Hi thanks for the response. I have been taking the voltage measurment using a digital multimeter with the bulb removed. I took the readings at the light socket that had a standard filiment bulb fitted.
Hi John. No the bulb is removed when I take the measurement and I am using a digital multimeter.
In which case you may just be measuring a capacitivly coupled voltage due to the long runs of wire that will be required for the two way switching. Digital meters place so little load on the circuit under test that they can get seriously wrong readings in cases like this (well to be fair they are right - the voltage is there but at a very high impedance, so if you try to draw any noticeable current it would quickly fall to zero).
If you repeat the measurement with an ordinary filament light bulb in place you may well get a very different reading.
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