DIY Doctor UK DIY Forums

In my lounge I have 2 light fittings each one operated by a 2 way switch. After we had decorated we decided to change the 2 light fittings for new ones and to use G9 LED bulbs. The fist one was fitted and worked fine, the second one was fitted but I only had 2 bulbs (needed to reorder) I plastered all the damage left by previous owners JOB DONE. This now gets interesting, the sun went down and then noticed the LED bulbs in fitting 2 were glowing (the voltage on my meter read 55volts) When we switched the lights on we got full brightness using the other switch to turn them off they still glowed.
Changed the switches no diff, replaced the inter switch wires no diff, the live wire in switch one fed switch 2 with the link wires removed the voltage was 235v, with one link wire refitted we still had 235v but the other wire when connected at just that one end reads 55v.
Where did it come from ?

Transmission lines is a huge subject. In the main 50 Hz is not high enough frequency to worry about but talk to any CB'er and he will talk about SWA or ham and VSWR and balanced loads.

In theroy there will be an optimum spacing between the line and neutral where inductance and capacitance cancel each other out. For this to work the whole idea of sending line only to the switch is out they must both run together.

However in the UK we use the ceiling rose as a junction box and only send line to the switch which has some marked advantages like running ceiling fans and emergency lights plus a better loop impedance. But the down side is an out of balance system with the effect you have found.

Some people fit suppressors and the capacitor inside the suppressor is enough to balance the system but it is hit and miss unlike with the radio ham and CB'er we don't have any meter to measure the reflected current so we can't work out when we have reached to balanced point.

Just to add to this some bulbs have the suppressor already built into the bulb so one make will work fine and another will either flash or glow dim.

As the load increases the problem goes away so once you have fitted all the bulbs it may work fine. It is normal it's nothing you have done wrong.