Voltage on light when off....?

5 Jul 2008
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United Kingdom
I was hoping someone could provide some advice.

My downstairs hall light will not switch on. It is a halogen (10x 10w) light from Ikea. It has a 105VA transformer stepping down from 240 to 12V AC.

The input to the transformer (measured with digi multimeter) is 240v when light switch is on but output from transformer is only reding 1.5v - I presume this means the transformer is faulty?

Also, when the light switch is off I am reading about 40v between the switched live and neutral feeding the transformer. Is this normal or does it indicate a fault and possible reason for the transformer failing after 6 months of use?

The 3 way switch in the hall also feeds an outside light. This also blows bulbs regularly (once a month) and there is a residual voltage of about 40v when switched off?

Are these induced voltages or is there something more serious and if so how can I fault find. I am relatively good with electrics but this is a new one on me.

Please help.

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Sounds like an induced voltage to me.

Your multimeter has a high impedence, so will read the voltage even though the current is very very small.
Using a good quality volt meter (£30).

Would the induced voltage be the reason for killing the transformer and the outside light regularly?

Whilst it is only 40v I presume this means the kit is always slight under load and therefore shortens its life.

Thanks for the quick reply by the way!!!
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It is unlikely that this is the cause of your problems.

The voltage that you are reading has an incerdibly small amount of current as it is induced, and will not actually be capable of powering anything other than a high impedence volt meter.

What type and brand lamps are you using in the outside light?

How old is the ikea fitting? The are not renownd for their build qualtiy. Have you been fitting the right size replacement lamps?
Hall light is less than 6 months old and is on original set of bulbs.

I typically use B&Q value 40w for outside - do you recommend something different?

Is 40v not unusual for an induced voltage?

Thanks for the feedback so far.
well thank you for being so honest. but would it not be a better idea to use a well known brand of lamp which will last longer, or even get a CFL
i guess so, I just wanted to make sure that I don't have an electrical fault given the voltage present when the switch is off.
So based on the symptons is it likely that the transformer is dead an reqires replacement?


probably, being ikea it will be cheap

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