DIY Doctor

Flickering lights.

Postby Frank Hair » Fri Aug 01, 2008 2:32 pm

Hi Peeps
This one has been asked before but there is more. I have just replaced the lights in a house in Spain and they have been inspected and signed off by a Spanish electrician but there is a problem with the low energy bulbs that the owner of the house wants to use. When they have been on for a while and then switched off they flicker (this is the question that you have answered in the past) the switch is new(standard on and off no dimmer) and so is the wiring and the lamp holder. In Spain the way things are wired is there is a main circuit for the sockets and one for the lights and each light or socket is on a spur from that main circuit. All of the wires are run throw plastic tube called macaroni, 2.5 multi core for sockets and 1.5 multi for the lights. When I check the voltage at the lamp holder with an AVO when the switch is in the off position I get 77 volts if I disconnect the switch so the live feed to the lamp holder is broken I still get 77 volts. The house is earthed with a 1.5 M copper and steel rob driven into the ground and all of the earths for the house are connected to this via a 6mm multi cored wire. It is a radial main with no return to the consumer unit. Unlike most houses over here it has a duel pole mains switch (they like to use a single pole mains switch on the neutral side).
Frank Hair
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Simply Build It

Postby ericmark » Fri Aug 01, 2008 7:26 pm

Dear Frank,
As I am sure you realise the UK system is different from many other countries and although our regulations are supposed to be harmonised with Europe it would be very easy to give you wrong information.
1) As in the UK both Neutral and Line are considered as Live in fact even more so than UK because of reversible plugs.
2) Using an earth spike with also require the use on RCD’s
3) Running cables in conduit can cause both capacitive and inductive problems and power can transfer between cables.
4) Florescence lamps as shown with the tube under pylons trick do not need much energy to glow.
5) Voltage needs to be measured between two points 77 volts switch cable to where.
6) With earth spike system i.e. TT there can be a large difference between neutral and earth in this country 50 volt would be considered limit. But in Spain this may be more.
If we are looking for a fault I would look for Line and Neutral being swapped and not necessarily on the lights. But it could happen without any real fault existing.
In this country it is not allowed to switch neutral except where double pole switching is used and it is switched with live.
Can’t see this as being much help but a start at least.

Postby Frank Hair » Mon Aug 04, 2008 3:41 pm

Hi Eric
This has helped I thought that there could be induction problems but we have kept the lighting and socket conduits separate.
There are RCDs fitted and the 77 volts is at the lamp holder between the live and neutral and it is still 77 volts when I disconnect the switch (only the neutral wire connected to the circuit the live wire is waving in the wind picking up electrons from the atmosphere). We only have 2 lights with this problem now they are 2way down stairs and one up stairs but the feed to the lights goes behind the consumer unit. Could this be causing the inducting problems or is it too far away (about 60mm between wire and RCDs).
Once again thanks for your advice we will keep looking. I have suggested using standard bulbs but they want to use low energy bulbs.
Frank Hair
Rank: Labourer
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Joined: Fri May 02, 2008 4:36 pm

Postby ericmark » Tue Aug 05, 2008 11:14 am

I will guess somewhere a Line and Neutral has got mixed up. (Since Neutral is considered Live we call the other wire Line) It could also be a simple as an indicator lamp. In some countries for example a light is included in the switch wired across switch contacts to light switch when off but you say wire disconnected.
The 77 volts without more info means very little. Old meters use to be rated as ohms per volt and with an old AVO mark 8 you may measure 70 volt on one scale and 120 volt on next scale up because resistance of meter had changed.
The pick up enough power to run an energy saving bulb one would have thought it would need a fair length a cable in close proximity.
The only time I have had this problem was in a radio shack where RF was being picked up by the cables and only when transmitting on certain frequencies.
My only suggestion is to try switching off other circuits and see if any have an effect on the measurements. Pulling cables through conduit can result in damage to cables and maybe you have some fault as a result.
If you find fault would be interesting to hear what it was.
Sorry not much help.

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