Lights dimming

[Can2002]

We moved into a new place last December and our surveyor warned us to get an electrical inspection done.

The outcome of the report showed a number of areas that needed attention, but one thing that did not come up on the report is that if any high power device is switched on (e.g. electric shower, drill, oven, etc.) the lights dim slightly. The dimming is not huge, but definitely noticeable.

I've done a quick survey of each of the MCB's off the consumer unit and confirmed that the lights (with one exception) run off dedicated fuses.

Am I right to worry about this, and if so, can anyone suggest what is happenning?

Cheers, Chris

[wanderer]

Probably not; If you had an inspection carried out, it would be worth asking the electrician who did the work if he checked that there weren't any loose connections on the meter tails.

Are you in a rural location? Do you have overhead cables to feed you or is everything underground? Do you notice the dip in the lights when you're not switching on something in your house? Are there perhaps any light industrial units nearby?

It could be a loose connection on the mains. If it is noticeable, then give your local electricity company a call - the ones who maintain the system - they may not necessarily be your energy supplier and tell them. There are limits for acceptable step variations in voltage on the distribution system. They will investigate, usually by installing a recording voltmeter for a few days. That will show if there's a problem on the incoming mains and whether it's in acceptable limits.

[Ian Stirling]

Are you capable of safely connecting up a voltmeter to the line, and measuring the voltage while a shower is turned on, and how much it drops from when it's off? Combined with the loads nominal wattage, this gives a very good idea of how much resistance the line has.

Some dimming is normal. It's probably going to be perceptible on most houses.

[Andrew Gabriel]

Filament lamps produce an amplified change in light output for small changes in voltage supply. Changing to compact fluorescents might make the effect unobservable.

[Can2002]

Hi there,

Thanks for all the info, very helpful!

Chris

[Can2002]

Hi Ian,

Thanks for the tip, I'll test it out tomorrow.

Regards, Chris

[The Natural Philosopher]

You have a crap incoming supply.

I used to have this till I paid a firtune to have a kilometer of overhead 11KV line taken underground (it ran slap over the back garden)

In the process a piddly little car battery sized transformer up a pole went, and was replaced with a huge transformer the size of a small garden shed in the garden corner.

No more dimming lights when teh microwave kicks in. Period.

[Ric]

Why did you have to pay? I would have thought that if the supply wasn't up to standards the supplier would have to pay?

[Can2002]

Following a tip from Ian last night I measure the drop in voltage when switching on a higher power device.

Prior to running an electric shower I was seeing 247 volts (it fluctuates quite a lot up to 248V). With the shower on it dropped to 234V. This seemed like quite a large drop, does anyone agree?

I'm not dure of the rating of the shower, so I repeadted the test with a

2.4KW fan heater. This time the voltage dropped from 247V to 240V.

I'm going to give the electricity board a call, but would welcome any feedback.

Cheers, Chris

[Lurch]

On Thu, 6 May 2004 16:58:54 +0100, in uk.d-i-y "Can2002" strung together this:

Problem is, although it's quite a fluctuation it's still within the limits so they won't be overly bothered. Worth a shot though. I still don't know what type of supply you have, what size it is and how old it is but if it's an oldish overhead then what you're seeing is the norm. The only way to solve it is run in a new 100A underground supply but that could be costly. Even then it depends on how far from the substaion you are.

[The Natural Philosopher]

I paid becuase I didn't acually want a bigger transforner up an even uglier pole. I wanted to get rid of a 600 meter section of 11KV line that crackled and buzzed over the patio, and was in the way of the house I susbesquently erected...the transformer they threw in for free :-)

>

[Colin Wilson]

216v is the lower end of the limit so you`re well within the boundaries.

Are you fed by a rural network, or are you in an urban area with mainly undergrounded cables ?

It could be that a fuse has blown in a substation feeding one end of the cable, so in effect you are now fed radially (one way) rather than from both ends.

Many overhead lines are radial by design, so if you are more rural you may well be stuffed unless you get something a little more damning.

[Can2002]

You were right, although I was fairly impressed as they were willing to make an appointment if I really wanted to. I decided to hold off for now.

It's not an overhead, it appears to come from underground. I don't know whether this is relavent, but when we first moved in the meter and main fuse were exposed to the outside air (albeit under a small porch). I managed to get the board to fit a plasit enclosure a while back, but one of the items picked up by the electricians report was that the fuse looked quite worn. I still have a slight problem here as the isolator switch is still exposed - I'm trying to find a lockable replacement.

Thanks again for your advice. I guess the main thing is that I know it's not dangerous. I may ask them to come out and check it to play safe.

Cheers, Chris

[Pete C]

If CFL's can't be used and the power company won't do anything, then maybe running the lighting circuit through a power conditioner would do it:

cheers, Pete.

[Lurch]

On Thu, 6 May 2004 21:31:29 +0100, in uk.d-i-y "Can2002" strung together this:

It could just be the last run from the pole to your house that is underground, it could be overhead for miles across the country.

Possibly, it wouldn't hurt to get them out to have a look. If the fuse holder is a bit on the loose side then that could be contributing to the problem and could get very serious over time.

I'd get them out to look at the fuse at least.

[wanderer]

Don't be put off by the comments about it being within limits. The supply voltage can be as low as 216volts, but what you are experiencing is a step change in the voltage giving rise to flickering lights. There is a statutory limit on the size of this step change. I can't remember what the figures are now, been out of the industry too long.

It won't cost you anything for the leccy company to check the supply voltage, in your position I'd get 'em to check.

[The Natural Philosopher]

Any high resistance in the incoming mains can cause this.

[Can2002]

Following my last post I tried measuring my voltage with more high power devices attached (both showers, over, microwave & kettle) and this time the voltage dropped to around 215-216V.

I rang EDF energy again and they sent someone out yesterday afternoon. Strangley all he did was disconnect the main fuse and measure the voltage coming in to the meter, which was 247V. He drew a conclusion from this that their line was OK and it must be my wiring!! When I pointed out that when I measured the voltage with minimal load it showed 247V too, and that it was only when under load that the voltage dropped, he basically shrugged his shoulders. The only suggestion he could make was that the high and low power devices must be running off the same MCB, but I've already confirmed this is not the case.

I'm not sure what they're going to do next, but it basically seems as though some link between the substation and my internal wiring has higher resistance. Earlier postings from others seem to suggest it's the supply to my house, but I guess I should try to test the resistance between the main isolator and my consumer unit. Does this sound like a reasonable idea?

Cheers, Chris

[John]

----- Original Message ----- From: "Can2002" Newsgroups: uk.d-i-y Sent: Saturday, May 08, 2004 10:44 PM Subject: Re: Lights dimming

I'd insist (as best you can) that they install a recorder to monitor your supply voltage over a period of time.

From your previous comments (fan heater, oven) I'd say you're looking at a supply impedence of between 0.4 and 0.8 ohms. I'd consider this "on the high side" and be concerned therefore about any impact on the earth loop impedence. If your report highlighted any earthing issues I'd hope that they've been remedied.

I'd not be surprised if your supplier didn't want to do much about this volt drop! What actual problem does it cause you?

JR

[wanderer]

Their first attempt will be to try and fob you off.

The intial contact from them is usually a craftsman. He won't know that much about the technicalities of the supply from the substation to your main fuse. What he should definitely have done was to put a screwdriver on the terminals of the main fuse, just to make doubly certain that there was no loose connection there.

'Phone them back again - make sure you get a name - tell them that the problem persists and please could you have a recording voltrmeter installed.

Can't remember how much info you've given - are you in a rural or urban location? I seem to think you said you thought you had an underground supply coming in, but do you have overhead cables out in the street?

I'd leave it alone now, and tell EDF that you think there's a loose connection somewhere on their system and what are they going to do about it.