Strange effect of dimmer switch failure

[Grindstone CowboyParticipant @grindstonecowboy]

Just had an odd problem with my house lighting – my daughter turned on the light in her room, which has a dimmer switch, and all the lights in the house went off. OK, I think, it’s just tripped the breaker. Quick trip to the garage, where I instinctively turned on the light – and it came on! The lighting circuit had not tripped after all (the garage is on the same circuit, proved by flipping the breaker). After half an hour of head-scratching, I thought since the dimmer being operated had caused the fault, what happens if I replace it with a normal switch? Result – everything back to normal.

So my question is this – how does a dimmer switch failure cause every light on the circuit AFTER that light to not work?

Rob

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Rob, I’m not saying it’s the same thing, but a while ago I had one or two lights that suddenly went dim and or went completely off, this seemed to be completely at random and didn’t happen every time. However, it came to a point where all the lights in the house went off when I turned on a hot tap. It turned out to be a connection in the supply to the house that  had corroded inside, which caused a high resistance, which caused a big voltage drop to the LED bulbs, when the boiler cut in to give me hot water. The electric people came and fixed it without any charge, as it was before the meter.

Regards Nick.

[Robert Atkinson 2Participant @robertatkinson2]

Most likely cause is that there was a faulty connection at the switch. Specifically in the live feed which is looped from one switch to the next. Thus a break at the switch stops downstream lights working.
It is also common to loop the feed in the ceiling rose so might be a bad connection there which has been “disturbed” by the current of the dimmer failing.

Robert.

[noel shelleyParticipant @noelshelley55608]

May be it’s just me, but one seems to find more poor connections that cause heating and then varying degrees of failure of modern times. I’m with Robert, that a loop in connection has some how failed. If an ordinary incandescent  bulb fails, by failing the circuit goes open circuit and resetting the MCB or trip brings the lights on. If an LED bulb fails it may be the control circuit, the fault will still be there and you cannot reset. Now in the dark you have to find out which lamp has fail – not always that easy. Lighten our darkness we beseech the oh Lord ! Noel.

[Grindstone CowboyParticipant @grindstonecowboy]

Thanks chaps, I will check out the looped connections (these must be in the rose as only two wires at switch) just in case it was a coincidence and there’s still an issue. Unexpected bonus is getting rid of the dimmer so I can finally put an LED bulb in there 🙂

Rob

[noel shelleyParticipant @noelshelley55608]

Rob, remember that the loop in connection is live even when the light switch is OFF. Throw the MCB or remove the fuse and then check with some sort of tester/ multimeter that it is dead. Good luck. Noel.

[Grindstone CowboyParticipant @grindstonecowboy]

Thanks Noel, breaker will be off and access to consumer unit locked. But will probably not get to it until tomorrow now, I’ll update if anything discovered.

Thanks,

Rob

[NealebParticipant @nealeb]

There are dimmers which work well with LEDs, of course. They get a little confused if they are driving a mix of LED and halogen – I’m gradually replacing wall light halogens with LEDs as they fail – but they still work. The dimmers I use can be configured to trim leading or trailing edge of mains pulses which can help with some LEDs, and can also be configured with a minimum light level rather than zero. Can’t remember the make offhand, I’m afraid.

[SillyOldDufferModerator @sillyoldduffer]

For what it’s worth I’ve bumped into similar strangeness in 3 different homes.   Intermittent cross failure of two ceiling lamps in Castle Duffer;  son’s top floor stair lamp; and sister’s fridge/freezer and oven.  All in older properties, and nothing to do with new-fangled technology!

Root-cause was loose connections.   The length of wire available was on the short side, making it awkward to get wire ends into  terminal holes and be sure the screws had gripped properly.  Pushing back into the mounting stressed the wires making it likely they would loosen, and I’m sure alternate heating and cooling of the connection over time does the same.

The Copper in my son’s ancient Red, Black, Green wiring made it even trickier to seat and clamp the wire correctly in the terminal. It’s noticeably harder and springier than the modern Brown, Blue, Green/Yellow stuff.   Another mystery – why should his old wire be hard and springy?  I don’t believe undisturbed Copper hardens with time, or that anything other than pure Copper was used to make it.  Presumably son’s wire was work-hardened during manufacture and then not fully annealed, perhaps deliberately.  Not fully annealing would reduce cost, or maybe springy wire is somehow useful.

Didn’t help that these fixtures were so close to the wall/ceiling that I had to check connections with a dentists mirror.   I cursed the original installers: much easier to make good had they left the wires 15mm longer!

Reminds me of the German Battleship cock-up, I think Tirpitz.   During fitting out much of the ship’s wiring was pulled tightly into the terminal boxes, which looks neat and resists vibration.    The work was done during a hot summer. followed by an exceptionally cold winter,  In the cold,  thousands of wires contracted enough to cause gazillions of intermittent faults.  Long delay whilst the ship was rewired…

Dave

 

[Grindstone CowboyParticipant @grindstonecowboy]

Well, further investigations postponed for a while due to car failing its MOT 🙁

But regarding SOD’s work-hardened wires, I have come across a similar issue with old copper gas pipes (tubes?) which will just crack if you re-use a length and try to bend it. I think it’s an age thing – the human body is similar.

Rob

[blowlampParticipant @blowlamp]

I don’t want to divert this discussion, but does anyone have any knowledge about ‘shared neutrals’ between upstairs and downstairs lighting circuits?

After a change over to RCBOs from MCBs I seem to have uncovered shared neutrals in the lighting circuits as neither circuit would work without triggering both RCBOs.

The temporary solution was to wire both circuits into the same RCBO, but of course that now means that a fault anywhere in either circuit knocks off ALL lighting.

I know shared neutrals used to be done with landing lights and hall lights so that either could be operated from upstairs or downstairs and this is indeed the situation I had.

I managed to resolve that problem by permanently isolating the hall/landing circuitry from one another by fitting wireless light switches and this has had the bonus of being able to add other switches in the most convenient locations.

However, wiring the circuits back to their own dedicated RCBO’s after separating the hall/stairs lighting has revealed that these circuits are still sharing their neutrals and I have no idea why this would still be the case.

I must admit that I don’t see why there would be a need for any further connection between both circuits

Can anyone provide me with some indication of where I should look next, please?

 

Martin.

[Grindstone CowboyParticipant @grindstonecowboy]

Hi Martin

I have no problem with diversifying the conversation 🙂

Not that it helps you, but I did once come across the two live ends of a ring main going into separate fuses on the distribution board, which raised an eyebrow or two.

Rob

[noel shelleyParticipant @noelshelley55608]

I would suggest that in this case an RCBO was the wrong unit for the wiring in the property. Our ever increasing aim of safety is not always as simple as it seems – or as cheap. Noel.

[Robert Atkinson 2Participant @robertatkinson2]

Any RCBO will trip on shared neutrals They sense the difference in current between live and neutral so if the load is connected to a different neutral there will be an imbalance and trip.
Unfortunatly the only way to sort it out is to get into the wiring and find the connections. A 50% rule helps. Tyr to isolate half the circuit at a time then split the half that still causes the trip in two again until you find the connection. There may be more than one…

Robert.

[Bill DawesParticipant @billdawes]

Coincidentally, when I recently decorated I removed a ceiling light fitting, it had 4 LED lamps on it and controlled by a dimmer switch, had worked successfully for several years. Decorating finished I replaced light, it came on albeit not at full brightness, dimmer made no difference up or down, suspecting  a bad connection for all the reasons above, I hate taking off and replacing with old or new, light fittings or sockets, especially ceiling lights where you can’t see properly where the cables are and they very often break off bits making it even more difficult to see what you are doing and getting them securely into the terminal blocks. So took ceiling light off again and reconnected but still no difference. Will try another dimmer to see if that is problem.

Bill D.

[Bill DawesParticipant @billdawes]

PS. Is it beyond the wit of the building supplies industry to design a domestic electrical system where you simply plug in power sockets and light fittings to a ring main fitted with the appropriate connections built into the system.

Bill D.

[Peter Cook 6Participant @petercook6]

Lots of options – look up (for example) “track busway” systems. However not very aesthetic, and not very child proof for use in domestic environments.

[Bill DawesParticipant @billdawes]

Yes I did think of the Bus system Peter but for the same reasons as you, not for domestic use , I think these are commonly used in shops as a ceiling system for example where they safely out of reach of Joe public.

[Grindstone CowboyParticipant @grindstonecowboy]

Just to close this off – I finally got time to do a bit more in-depth investigation whilst there’s daylight, and I traced it to a broken wire in the ceiling rose of the hall light (which is the first one after the consumer unit). Of course the screw was tight, and the natural spring in the wire was pressing it into the terminal, so it looked OK at first glance. Just fatigue from 45 years, I guess, plus maybe a few knocks to the light fitting.

So replacing the dimmer switch was a red herring.

Thanks again for all the help and suggestions.

Rob

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