Strange problem with new extension

[pablo1]

Hello!

First of all i am not an electrician but need some help on how to progress with a problem i have. I apologise in advance if i'm not using the right lingo but i hope i'm making everything clear.

We've just had an extension of our lounge completed. Electrical fittings were 6 double plugs on a new ringmain and several spotlights all controlled by 3x 3gang dimmer

Dimmer switches:

Dimmer 1
a) controls a single GU10 50W Spotlight
b) controls 2 GU10 50W spotlights
c) controls a set of 4 50W GU10 spotlights

Dimmer 2
a) controls a set of 4 50W spotlights
b) controls a set of 4 50W spotlights
c) controls 1 GU10 50W spotlights

Dimmer 3
a) controls 1 single GU10 Spotlight
b) controls 1 single GU10 Spotlight
c) controls 2 GU10 50W spotlights

The dimmers are getplc and rated at 60-300W per gang.

Every now and then we hear a loud 'bang' that appears to come from either the ceiling or behind a wall's plasterboard. A millisecond before the bang the lights (everywhere in the
house) dim for a fraction of a second. This could occur once every few hours or even a few times within the space of a few seconds. It also occurs when all lights in the lounge are off and also when there is nothing plugged into the lounge sockets.

The work was carried out by a building company and further inspected by another electrician. He performed wiring tests on all sockets, lights and fusebox and found no problem and he is equally confused. Unfortunately we had no 'bang' while
he was here which may have helped in diagnosis. We have the electrical installation certificate.

The only compatability issue here is the dimmer controls that control only one spotlight at 50W, rather than the minimum of 60W. The electrician said that the problem we have would not be caused by not meeting this threshold; the said light would only flicker.

So we are completely stumped and require opinions assistance from experts!!

Hope you can help.

Paul

 

[luminaire]

Where you have halogen lamps you need to double the rating.
I.e. 7 x 50W = 280W, your dimmer will need to be 600W.(dimmer 1).
Dimmer 2 will need to be > 900W, dimmer 3 > 400W.
Also for your extension you have added 930W to the lighting circuit. Is this a separate circuit or an add-on to your existing light circuit.
If it's the latter then maybe your circuit is overloaded. What size cable was used?
I think your wiring needs to be more closely looked at for loose connections, especially your sockets (not plugs).

 

[batco]

Do you have any transformer installed in the house? and what kind of consumer unit you have? do have any electric shower in the house?

 

[pablo1]

Firtstly thanks for your time and replies.

Do you have any transformer installed in the house? and what kind of consumer unit you have? do have any electric shower in the house?

It's a fairly new property (built 1984). Will look into what kind of unit it tomorrow. Also no electric showers in the house and this problem only started when the extension had been completed.

Where you have halogen lamps you need to double the rating.
I.e. 7 x 50W = 280W, your dimmer will need to be 600W.(dimmer 1).
Dimmer 2 will need to be > 900W, dimmer 3 > 400W.

Aah thanks. I remember at the time i knew this to be the case but forgot that we were going to buy spotlights with 4xGU10. Also are you not giving me the max. load per dimmer set rather than per dimmer control so Dimmer2, for example, should be 400W per gang rated. So do i just need to make sure that each gang is 400W or just that dimmer set total load needs to be 900W rated?

Also could it be a load problem given that it still happens when all the lights are off?

Also for your extension you have added 930W to the lighting circuit. Is this a separate circuit or an add-on to your existing light circuit.
If it's the latter then maybe your circuit is overloaded. What size cable was used?

I'm not certain but i believe the extension lighting is on it's own new circuit but will check tomorrow.

I think your wiring needs to be more closely looked at for loose connections, especially your sockets (not plugs).

The sound seems to eminate from behind our TV where there are sockets present so it could well be the case. Damn builders eh?!!

 

[pablo1]

I have had a look in the garage where the oringinal consumer unit sits and can tell you how the extension is powered:

ORIGINAL WIRING
From meter>Distribution box(Greenbrook 2289 120A 250V Max conductor size 25mm2)>Original fusebox>original house circuitry.

EXTENSION WIRING
From Greenbrook 2289>same thickness cable as above>RCD Volex Protector VB32VB>VB06 tripswitch (extension lighting) and VB32 (extension main).

Seems rather strange that the house lighting dims when this bang occurs if the problem is due to the extension as they are on separate circuits.

Have now turned off the extension lighting and main from the Volex Protector to try and isolate the problem.

 

[Dippy]

Where you have halogen lamps you need to double the rating.

Why?

 

[RF Lighting]

Because halogen lamps have a high inrush current which can damage a dimmer rated at the total wattage of the lamps.

AFAIK, the norm is to derate dimmers by 25% though.

 

[Dippy]

thanks

 

[sparkieno1]

This sounds like a short circuit probably L-N inside your wall,possibly a nail through a cable but it is surprising that no breakers trip(I take it you would have mentioned if they did).To find it you would have to narrow down as far as poss where the bang is coming from, isolate power then remove gyproc and check visible cables.I know this can be messy but sometimes its the only way.If the bang is coming from near any sockets I would remove faceplates and check cables coming into back boxes first(isolate sockets first)