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Lights Dimming


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Can you shed any light on this please..............

When we plug in or turn on an appliance, hoover and kettle mainly, our lights dim.

Talking to some guys in UK, they say it is to do with the power supply or lack of it. Having read a post to do with upgrading the supply for his proposed electric heating, I wondered if an upgrade is available and how.

Please elighten me!

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Speaking *very* generally,   if you're a long way away from a substation (ie there is a lot of wire between your dwelling and civilisation) you tend to find that as you increase the load on the supply the voltage drops significantly.

It's all to do with I squared R,  which I'm sure you don't want to be bothered with, but which quantifies the increasing heat loss in the cable as the current drawn is increased.

It's one of the reasons so much of rural France is three phase,   spreading the load over three wires allows EDF to use smaller gauges out to rural houses.

What to do?

If you're three phase then you might need to get someone in to rebalance your thirstier applicances so that they are spread across the phases more equally.

If you're single phase and it's a problem I'd try and get the voltage measured when you've got everything switched on,   and contact EDF with the result if it's below 205 V   (I pluck that figure because in Britain the maximum voltage drop permissible during - say - industrial action by miners or power workers was set at 6%;   more expert commentaries are no doubt available and will be along in a minute!)

Do you get the problem at all times of the day?    Is anyone else nearby affected similarly?

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Thanks for the reply, doesn't sound like there would be anybody too much more qualified than you! And easy to understand too, thanks.

We only notice the lights dimming because we have them on, which is I guess towards the evening. I don't know if the neighbours suffer a similar thing. The thing to do is ask when we go back out next week.

How do I know if I am single or 3 fase? Also, balancing appliances?

Crikey, sounds aggro!

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Rebalancing on a three phase supply simply means sorting things out so that -  say -  your kettle and dishwasher and tumble drier aren't all on one phase whilst a couple of lights are on another by themselves.    To be honest that's more of a problem if you find that the supply keeps tripping out at the disjoncteur;   the way EDF do things you pay the standing charge for a current (amps) limit on each phase;    nudge over the limit on any one phase and all three trip out.   Rebalancing is a job best left to a professional for a permanent solution  (it involves playing around in the fuse box) but you can mitigate things by moving such items as a kettle to another socket elsewhere in the kitchen and seeing if the problem diminishes.

On a single phase supply you again pay for a limit,   but because there's only one phase the equivalent limit is three times what it would have been on a similar three phase,   so instead of having a trip on a 20A per phase limit when you use 21 + 3 + 1 amps you only trip out at the full 60.   Again,  simply speaking.

If the lights only dim a little bit then it's nothing to worry about.    We have a similar problem which is in part influenced by what other people on our supply use (I can't call them neighbours exactly as they are about a km away).    A good test seems to be the hairdryer,   it produces a noticeably lower note when the voltage is down,   I don't think ours ever drops below 205 V ish   (I will try and remember to check so if you hear a bang from the direction of Perigord you'll know it's me).

You'll only have a problem with a heavy duty motor,   they don't like a significant drop in volts.    Our lawnmower is an example,     put it on a long (50 m) extension cable and you can hear it struggling to get going.    But that's exceptional and you can tell from the note that the motor isn't happy.

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We have had a rewire done to the living area, not the cave. And we are not using the kitchen (because its not in yet!), but the electrics have been installed. I will try the kettle in the kitchen and see if there is a difference, because the kettle has been from room to room at the moment!

We have had a 2 way switch put in at the top and bottom of the basement stairs. First time I tried the switch from upstairs, it popped from down stairs and then wouldn't come on at all. Later in the evening I went to check around before going to bed and the downstairs light was on? The 2 way switch maybe is connected to the original electrics in the basement? Would this cause the problem, they do look a bit 'iffey'.

I'll look next week when I am back in France for the 'triphase' on the consumer unit.


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[quote user="nemltd"]We only notice the lights dimming because we have them on[/quote]Classic [:D][:D][:D]

Sorry, couldn't resist [8-|]

Excellent summaries from Martin however short of upgrading your power cables (which is unlikely to be a cheap prospect) there is a good chance that you'll never be able to eliminate the problem completely.

When electricity first came to rural france most properties would only have had just lights and perhaps the odd appliance such as a radio or two or maybe later a TV and couple of electric heaters etc. Nowadays of course demands are far higher and also tend to be concentrated in one or two areas, principally kitchens and utility rooms, so you can have a situation where virtually all your consumption is being drawn from one phase and although it might be able to cope with it in a 3ph system the neutral is common therefore, even if you had nothing but a single light on each of the other 2 phases, they could still dim in response to a heavy load on the 3rd.

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I'd forgotten that of course measuring voltage is now child's play with a consumption meter.

And as a certain member of this forum was kind enough to send me one a couple of years ago  (thank you gyn_p) I did check ours last night.

The lowest phase was at 216V,   which dropped to 213V when the hair-dryer was plugged in.    This is by no means as bad as it gets as the lights were not in any way dim,   but it shows that a 1000W load on an already droopy supply has quite an effect.

I'll try and check when the cooker is on......

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It is very common in rural France. An appliance that takes a high power for a comparatively short time, like a kettle or hair dryer, will cause a voltage drop. If there is a lot of loss - more likely to be in the power lines feeding your house than in your system - upgrading the supply level is not likely to make any difference. If the power trips when you plug the kettle in, that's a different matter and an upgrade will help.

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  • 2 weeks later...
I hope some-one can help with this, too.

We have a tri-phase supply to the consumer unit (which is very old).

Then our electrician re-wired the house (which is big).

All goes well until the cheap rate time flicks on at 12.30, when the main fuse cuts out at the consumer unit rather frequently.

Sometimes this happens at 13.15 hours, rather than when the cheap rate starts.

It doesn't happen during the night time cheap rate.

How can I find out what appliances are connected to which phase, as I would hazard a guess that an overload on one phase is tripping the system - or will it be too high a demand overall at lunch time?  How would I know which???

A colleague suggests that too many high usage appliances may be connected to one of the phases and that although our supply is 15 kws, if it's shared over 3 wires then this gives each only 5 kws which won't be enough - could he be right?

I need very simple replies as you can tell I am not electrically competent! (I do understand circuit diagrams, however).

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