Wiring problem

[forester]

My house was built in the 70s, and the wiring dates from then, except that I recently had a fancy new fuse box fitted, plus a new fuse box for the shower. This problem existed before these were fitted...which is simply that, for example, if the shower is switched on, the lights dim perceptibly. It can be appliances in different rooms, or even different circuits, as the shower example shows. I can't really say if this is getting any worse - it may be that I am just noticing it more. I don't know if there is a connection, but I do seem to go through a lot of light bulbs. My overall electric usage is probably about average, heating is gas-fired, gas cooker, etc.

Any ideas? Nothing untoward was found when the new boxes were installed, although the old ones were of the fuse wire type. Thanks for any help.

Norman

[brugnospamsia]

where in the house was the shower fuse box installed, and why was it seperate from the main one ?

[forester]

fitted...which

The shower fuse box is right beside the main one, downstairs. And I thought shower fuses were supposed be a separate circuit. But I really dont think there is a link...if I turn on a fan heater in my office, the ceiling light dims...not by much, but it is noticeable.

[Dave Jones]

Could be a faulty meter, restricting the current flow when under load. Ask your Local Electricity Board to check the meter.

[Stefek Zaba]

A barely-perceptible dimming is quite normal; just how much you get depends on your supply. At one extreme, if you're sharing a pole-mounted transformer somewhere out in the sticks with a few other houses, and your distribution board's a little old and wired with 16mmsq tails, 40A of shower load will cause noticeable dimming. At the other extreme, if you're in a city street with a normally-hefty substation close by, and your supply and tails run in gert big cable (25+ underground, 25mmsq tails), you wouldn't notice much. There'll also be more variability if the local transformer/substation has become undersized as extra premises have been built since it was specced - and that could account for

if the transformer's taps have been set to give a high-enough voltage somewhere Further Away while you're Close (for suitable values of Further Away and Close, you understand...)

You might be able to persuade your electricity supplier to persuade the real supply company to put a voltage recorder into your premises for a week or so, to see if the supply's within limits, including when you draw loads within the limits supplier's main fuse. If there turns out to be a fault on your side of the meter, they'll charge you...

[forester]

fitted...which

pole-mounted

premises

Thanks, chaps. I am out in the sticks, but I will say that the Leccy Board replaced the pole mounted stuff not so long ago (the problem precedes that) and my neighbours dont have the problem. I think I'll have it all looked at by the supplier.

[Stefek Zaba]

It could be something as simple - but potentially dangerous - as the meter tails being not well tightened when the new CUs were installed: there'll likely be several connections (at meter, at oversize junction box, and from oversize junction box to both CUs - your main one and the separate one for your shower). Before getting the supplier in - since you say neighbours' supplies seem OK - any chance of getting whoever did the CU work back to take a quick look for you?

[forester]

junction

I had this problem before the new CUs were fitted.

[John Rumm]

The dimming of the lights does not indicate a fault as such, although the high rate of light bulb attrition might indicate your supply voltage is a bit on the high side.

The dimming is caused by the voltage dropping as the load increases, as Stefek described. I have seen quite noticeable dimming even in properties in the middle of a town when a 40A shower kicks in.

Depending on what test equipment you can lay your hands on, you could investigate a little before calling in the electrickery company. A volt meter (or multimeter) will tell you if your supply is high (more than

253V and it would be out of spec). Again checking the voltage on (for example) a socket circuit when the shower is turned on, you would expect to see a slight fall in voltage. If however it dropped to under 215 volt then that would another reason for the supplier to check their supply.

[John Rumm]

Which would tend to eliminate much of your CU wiring from the equation....

[Andrew Gabriel]

Besides the other comments, i.e. check what the voltage drop really is in case it's a bad connection in the supply which should be fixed, you might be able to mitigate the effect by switching over to compact fluorescent lamps. Filament lamps greatly exaggerate the effect of small voltage changes with much larger brightness changes. A compact fluorescent (or regular fluorscent with electronic control gear) will very likely show no brightness change for significantly larger voltage changes.

[Pete C]

Hi,

A cheap DVM or one of those plug in power meters will give some idea what the voltage is doing.

cheers, Pete.