110V present with light switch off

[Andrew Harland]

Hi all,

I went to a property to replace a dining room light which was not operating.

The dining room had two switches which both switched 1 light on/off.

I tested for voltage at the light and noted when switched on that 230v AC was present.

When off 110V AC was present.

Any ideas? Thanks in advance.

Andy

 

[SparkyChick]

What did you measure the voltage with? And was the 110v L-N, L-E, N-E?

If the instrument you used has a sufficiently high input impedance, there will be minimal current flow and the voltage could simply be an induced voltage on the cable (either from inductive or capacitive coupling when running next to other cables).

If you used an AVI they typically have a much lower impedance meaning a greater current will flow and the voltage will disappear if it's induced in some way.

Failing that, sounds like you should be giving that circuit a thorough test starting with continuity (looking for bad joints) and IR.

 

[Pete999]

What did you measure the voltage with? And was the 110v L-N, L-E, N-E?

If the instrument you used has a sufficiently high input impedance, there will be minimal current flow and the voltage could simply be an induced voltage on the cable (either from inductive or capacitive coupling when running next to other cables).

If you used an AVI they typically have a much lower impedance meaning a greater current will flow and the voltage will disappear if it's induced in some way.

Failing that, sounds like you should be giving that circuit a thorough test starting with continuity (looking for bad joints) and IR.

Beat me to it with the first part. Agree with the rest though.

 

[Adam W]

Is the light still not working?

 

[telectrix]

looks like OP has legged to the Tyne Bar. think they open @12.00.

 

[westward10]

Is the light still not working?

It is fine he has fitted a 110v lamp.

 

[Wilko]

The dining room had two switches which both switched 1 light on/off.
I tested for voltage at the light and noted when switched on that 230v AC was present.
When off 110V AC was present.

Hi - 230V must be present on at least one terminal of one switch. Then the switched terminal is either 230V when the switch is closed or when it's OC the terminal may float, depending on connected load. Hope that helps .

 

[Spoon]

It is fine he has fitted a 110v lamp.

Class reply... laughing sooo much I have tears in my eyes..

 

[sparksburnout]

I hope you don't think I am being disrespectful here, but your profile says you have a HND in Electrical Engineering, plus a C&G qualification in Inspection and testing. I presume you are a Sparky as you say you "went to property to change a light switch", so I am just curious to know how do you manage to get through the day if you can't sort out a simple 2 way light switch problem?

 

[Andrew Harland]

Hi guys, The measurement was taken between L-N with a Fluke Multimeter. The Light was disconnected before measurement was taken. I reconnected it and measured either side of a transformer which was in the rose. It had 230V in but nothing out. I assumed the transformer was goosed.

 

[telectrix]

quite possible that the transformer has shut down if the load was removed.