How is this lighting fault even possible?

[wobaguk]

Got a weird fault I am trying to diagnose, and its twisting my brain...

The living room light flashed on switch-on, then wont come on. OK a bulb probably blew, check the Lighting fuse on the RCD, nope (reset it anyway just in case), new bulbs dont work, definitely not the bulbs...

Two other independent lights nearby now dont come on. They dont work on the same switch, and EVERYTHING else on the lighting circuit is working fine.

I thought I understood how a lighting circuit (as a loop) worked, but this seems to contradict it. What am I missing?

Thanks

 

[kerching]

Switch

 

[Murdoch]

neutrals

or are they dimmers?

 

[wobaguk]

Switch

The switch was my second thought, however I dont get how this impacts two other lights on independent switches, while not impacting every light on the circuit.

 

[wobaguk]

neutrals

or are they dimmers?

Nope no dimmers. And all using LED bulbs.

 

[Andy™]

loose connection most likely

 

[SPECIAL LOCATION]

Broken, lose, damaged connection somewhere earlier in the circuit.
.
Possibly an old poor connection gradually deteriorated over time due to the cycle of heat caused by the normal current flow..

e.g. a loose screw connection can be functional for a long period of time with arcing/sparking repeatedly weakening the joint, until it finally fails.

Whole circuit needs a bit of dead continuity testing in my opinion.

 

[Murdoch]

Be VERY wary of how you poke around ........ they may not be dead................

 

[wobaguk]

Be VERY wary of how you poke around ........ they may not be dead................

No fear, short of something super straightforward, I dont get my hads dirty. Any open ended 'poking around' will be a professional.

 

[Andy™]

Be VERY wary of how you poke around ........ they may not be dead................

even worse, the neutral may be live

 

[binky]

The switch was my second thought, however I dont get how this impacts two other lights on independent switches, while not impacting every light on the circuit.

Lofts are wired in series, loop in , loop out and a switch line, otherwise known as 3 plate. So if you have a dodgy connection at one light, in takes out the lights fed from that position.

 

[BorisJ]

Lofts are wired in series,

??!
No they are wired in line.

 

[binky]

??!
No they are wired in line.

Ruddy auto correct, that should say lights not lofts.

In series, you go from light to light with the permanent live/ neutral and earth. Not sure I've ever encountered anyone describe that as in line. Daisy chained is a term non sparkies might understand better

 

[UNG]

Daisy chain is a term that is used in a lot of technical manuals so not limited to non sparkies

As for wiring lights there are a number of methods that could be used the most common being the loop in / loop out at the light fitting

To say lighting is wired in series implies something like Christmas tree lights when fixed lighting circuits have the lamps wired in parallel between the live and neutral

 

[poni]

In series, you go from light to light with the permanent live/ neutral and earth

I think you mean "parallel"

 

[binky]

I think you mean "parallel"

Nope parallel would be spider wiring

 

[poni]

To say lighting is wired in series implies something like Christmas tree lights

I don't want to get into a argument about this, as I know what you mean and yes the spider circuit is also a Parallel circuit, and was used before we used the 3 plate ceiling rose system,

 

[SPECIAL LOCATION]

Just for the sake of anyone who may be DIY'er, Still in training, Recently qualified, Just curious.... who may be following this thread and getting a bit confused...
I will try to clarify...

Excluding any volt-drop effects due to the cable resistance per meter of the circuit wiring...

With 99.9999% of single-phase domestic electrical installations...
in order to ensure the supply voltage is present at all of the the load(s);
Sockets / Lights / Showers / Cookers / etc.. etc..
{Note:- with a typical light the load also needs to includes the switch, otherwise the light will stay on all the time..}

They MUST be wired in parallel with a connection onto the Live & Neutral conductors, directly back to the incoming supply..

If any loads were wired in series, they would not get the full supply voltage...
As series wiring divides the voltage.. whereas parallel wiring divides the current..

[ This is often seen when a DIY alteration mixes switch live with permanent live..
leaving more than one room wired in series and the lamps glow dimmer due to the voltage division across the loads. ]

So every room's series connected switch & light, are wired in parallel across the supply..
with one or more lights connected along the length of the circuit cable.