2 way lighting problem...

[dynomo]

Went to a customers today for a basic plumbing job. He pointed out an issue with the light on his upstairs landing so I thought I'd take a look.
Established that the celing rose on the landing is linked to another ceiling rose in an adjacent hallway. Both are controlled by a 2way lighting switch system, i.e. one switch upstairs and the other downstairs.

The landing light worked fine and a multimeter test showed 240v between L+N. There was no bulb in the landing light originally. The hallway light however gave strange readings. I took off the bulb and connected multimeter to L+N and got 120v when the light switch was OFF. When switched ON, I got 240v....Now i'm sure you are meant to get 0V when the light is switched off!!

Then I inserted a 60w bulb in the ceiling rose in the landing. Switched it on = ok. The issue was that the celing rose in the hallway wasn't working at 240v when switched on, it only gave 120v!!!

I am normally one to post pics but can't on this occasion. I instructed the customer to invite a qualified spark to rectify the problem but I was ever so confused as I was leaving. What on earth could have been the problem??? I checked all connections at the roses and switches and all were sound.
Cheers chaps.

 

[dynomo]

blimey, wasn't expecting this....

 

[chris_1982]

hummm... no idea. i'm interested to know the outcome of this.

 

[Spark123]

To drop as low as that with a lamp inserted (did it glow?) is saying it is connected in series with another similar lamp. If it did glow, did another lamp glow elsewhere?

When it is open circuit, measuring voltage on switch wires using a high impedance volt meter isn't out of the ordinary, it is normally caused by capacitive coupling of the cables. Inserting a lamp will cause this voltage to drop off.

 

[holmslaw]

..

 

[dynomo]

To drop as low as that with a lamp inserted (did it glow?) is saying it is connected in series with another similar lamp. If it did glow, did another lamp glow elsewhere?

When it is open circuit, measuring voltage on switch wires using a high impedance volt meter isn't out of the ordinary, it is normally caused by capacitive coupling of the cables. Inserting a lamp will cause this voltage to drop off.

yes the lamp did glow but very faint, very very faint. But the light on the landing remained normal, just the hallway one that faded. I had a guess and yes the fact that it wasnt connected in parallel did cross my mind, but I gave up and advised customer accordingly.
Customer did get another spark in to look at the problem but apparently he wasnt able to sort it and referred it to someone else!!