Replaced bulb with LED....now it flashes when OFF?

Hi all

I've just replaced some bulbs with some 240v LEDs. Curiously, the LED at the top of the stairs now flashes every 3-4 seconds - when switched OFF. The light has a two-way switch at the top of the stairs and a two-way switch at the bottom. The feed comes to the top switch, loops down via a brown/grey/black cable to the bottom (black/grey feed down, brown is the return) and then into the light. The cabling *looks* correct in my limited experience.

I've put a meter across, and with the light switched OFF, there's around 12v in the cable. If I toggle both switches so the light is off again, there's 30v-38v in the cable, and this is enough to trigger the light flickering.

It's not the bulb, as I've swapped it with other LEDs, and I've also used a CFL and it flashes too.

I guess the  ~ 38v is enough to provide buildup in a capacitor in the bulb and it then discharges. But where could that 38v be coming from? I've no easy way to follow the cable run as it's in the ceiling above the stairs.

Confused.com.

Many thanks




Jim

PS Yes I've googled to death and still can't find any hint of a solution. It does seem to be more of a problem with two-way switching though.

 

Many thanks for the reply wally.

At the switch upstairs, where the light is, there's 2 core + e feed, a 3 core + e to the downstairs switch, and the 2 core + e for the light itself (single bulb).

At the switch downstairs it's spaghetti, as it's a 3-gang. I've switched off the fuse for the downstairs lights but it still flashes, so I'm not sure the induced current is being introduced at the switch.

Does that muddy any waters?


Jim

 

Many thanks spinlondon.

Sorting the wiring probably isn't practical, it's 10 feet above me in the plasterboarded stairs ceiling. The flash is evey 3-4 seconds; does that rule out the resistor option?

Jim

 

Ok what I've found is the effect is much worse on the black cable than on the grey cable. Looking at the cables in the outer sheath they are grey, then earth, then black, then brown, so black and brown are beside each other in the sheath.

I've now swapped black and grey at both switches. When both switches are in the up position (e.g. off) the live wire is the grey which is furthest from brown....and the problem appears to have gone away! At least, no flashes in the last two minutes anyway. Voltage across the contacts is 12v (can't measure the current accurately on my cheapo meter).

Time will tell. If it persists I might end up trying to run a new cable the length of the stairs in the ceiling



Jim

 

Thanks. I always check a circuit with TWO electrical screwdrivers whilst the circuit is ON, ensuring both glow, then re-check with the same two when the circuit is off to make sure they don't glow. I also check all the pins in the socket in case there's a mix of circuits, as there is in the downstairs 3-gang light as it controls the hall lights and the landing light.

Jim

 

To add closure to my original question. I have just got round to fitting one of these:

http://uk.rs-online.com/web/p/rc-network-capacitors/2067869/

Specifically, PMR209MB5470M100

as recommended in post #8 on this page:

http://www.electriciansforums.co.uk/electrical-forum-general-electrical-forum/63685-flickering-cfl-lamps.html

and it has cured the problem. I can now have the light off in either position (both switches up, both switches down) and the nlight is not flickering.

I have managed to fit the capacitor/restistor inside the junction box that's used to connect the ceiling light to the cable, so it's self-contained and insulated.

Many thanks all.


Jim

 

There is an RCD, yes, in the CU, but so far the two are playing together nicely.

Jim