Upstairs light circuit all down - MCB not tripped

[azibux1]

Hi all

Had a situation where one bathroom downlight (MR16) flickered, then they all went down but the MCB didn't trip.

Now none of the lights work upstairs and just wondering if anyone has any ideas please on what this may be?

I have read about a loose neutral and if I'm correct this basically means a break in the 'ring' / loop therefore not making a complete circuit... But how would this have happened without anyone fiddling with the actual cabling or installing any new lights?

Have a multimeter and fairly competent with these jobs, but anyone know specifically what / where to try and diagnose this issue best?

Each MR16 has its own transformer and I believe (was about 3 years ago now) we wired them in parallel when we did it so in case one blew, the rest would work - but as I say, it was a while ago so I may be wrong on that one.

Any advice is appreciated!

An electrician friend came round but only had limited time so couldn't find the issue. Wasn't home but I assume he checked the MCB as a starting point. Advised checking the transformers but if there is an open circuit then surely we won't see any voltage at the transformers anyway?

 

[ban-all-sheds]

Hi all

Had a situation where one bathroom downlight (MR16) flickered, then they all went down but the MCB didn't trip.

Was it just flicker and then everything died, as pretty much one event, or had it been flickering for a while? Is the circuit on an MCB, or an RCBO?

Now none of the lights work upstairs and just wondering if anyone has any ideas please on what this may be?

Probably that they aren't getting any power.

I have read about a loose neutral and if I'm correct this basically means a break in the 'ring' / loop therefore not making a complete circuit...

Could just as well be a dodgy live.

But how would this have happened without anyone fiddling with the actual cabling or installing any new lights?

Vibration or thermal expansion/contraction finally causing a loose conductor to fall out?

Rodent damage?

Damage to the cable where it runs through the house before it gets to the first light on the circuit?

Have a multimeter and fairly competent with these jobs, but anyone know specifically what / where to try and diagnose this issue best?

Each MR16 has its own transformer and I believe (was about 3 years ago now) we wired them in parallel when we did it so in case one blew, the rest would work

If that's why you thought it would be a good idea to wire them in parallel then your "fairly competent" has to be challenged.

An electrician friend came round but only had limited time so couldn't find the issue. Wasn't home but I assume he checked the MCB as a starting point.

You could ask him, rather than assume.

Advised checking the transformers but if there is an open circuit then surely we won't see any voltage at the transformers anyway?

If the bathroom is the first one on the lighting circuit then if a conductor has dropped out of a transformer terminal then that could break the whole circuit.

 

[azibux1]

Was it just flicker and then everything died, as pretty much one event, or had it been flickering for a while? Is the circuit on an MCB, or an RCBO?

Yeah just this one off time, one individual light flickered (so need to look at that specific transformer) then the rest all did the same simultaneously after then they didn't' come back on.

From what I can tell it is an MCB, there is a separate RCD on the board.

Probably that they aren't getting any power.

That seems to be the case, a break in the circuit somewhere.

Vibration or thermal expansion/contraction finally causing a loose conductor to fall out?

Rodent damage?

Damage to the cable where it runs through the house before it gets to the first light on the circuit?

Last one is unlikely as we haven't been doing any work.

Top two are possible and rodent damage shouldn't be too hard to spot. Just the loft is extremely hot today! Ha

If that's why you thought it would be a good idea to wire them in parallel then your "fairly competent" has to be challenged.

How so?

You could ask him, rather than assume.

I'm working but my Dad is home, so he knows exactly what was checked. Just haven't spoken with him yet.

If the bathroom is the first one on the lighting circuit then if a conductor has dropped out of a transformer terminal then that could break the whole circuit.

Will take a look and check the transformers when I'm back later

 

[Taylortwocities]

Forget the transormers, for now. If ALL of the upstirs lights do not work, then the problem is much more fundemental.
Start with checking there actually IS 230V leaving the MCB. Then you'l need to check the supply at each of the upstairs lights. Using your multimeter.

 

[azibux1]

Forget the transormers, for now. If ALL of the upstirs lights do not work, then the problem is much more fundemental.
Start with checking there actually IS 230V leaving the MCB. Then you'l need to check the supply at each of the upstairs lights. Using your multimeter.

Thanks!

I wasn't sure from reading online about loose neutrals/lives whether or not a break in the circuit somewhere would knock the whole circuit out and not allow power to anything. But as said that's quite odd as nobody touched anything unless it was movement on a loose connection somewhere.

Say for example 230V is leaving the MCB, and a few of the lights do not have any supply... What would be next then?

Should at least one thing have power unless of course it is the first one in the loop?

I assume of course if the loop is broken then nothing after that has power, but does that also mean the things before the break won't have any supply as they won't have a complete circuit either surely?

 

[EAST61]

You've mentioned ring/loop a few times now, but aren't lighting circuits normally wired into a 6a radial?

 

[EFLImpudence]

I wasn't sure from reading online about loose neutrals/lives whether or not a break in the circuit somewhere would knock the whole circuit out and not allow power to anything.

If it is before the first one, it will do that.

But as said that's quite odd as nobody touched anything unless it was movement on a loose connection somewhere.

from your description it sounds like a loose wire which was touching and now isn't.

Say for example 230V is leaving the MCB, and a few of the lights do not have any supply... What would be next then?

Check the terminations at the first lamp - probably the nearest in one direction or the other.

Should at least one thing have power unless of course it is the first one in the loop?

Correct.

I assume of course if the loop is broken then nothing after that has power, but does that also mean the things before the break won't have any supply as they won't have a complete circuit either surely?

It's not actually a loop. It is a radial circuit - a line from CU to light to light until the last.

We do call it looping in and out at each light - but the circuit is not a loop.

 

[azibux1]

Thanks for the clarification EFLImpudence! That will help with troubleshooting a lot! Done work on bits here and there but never actually got to the 'end' so didn't know if it goes back to the CU or not.

So just to make sure my understanding is correct.

Say we have lights 1, 2, 3, 4, 5 and 6.

If there was a loose wire in 3, it is quite likely that anything 'after' 3 also won't be working?

From the fact we have no lights working (based on the above understanding being correct) - I assume our fault is the MCB or the first light in the circuit

Will be able to check it out later hopefully and get some progress

Happy to hear ideas still in the meantime

 

[EFLImpudence]

Say we have lights 1, 2, 3, 4, 5 and 6.
If there was a loose wire in 3, it is quite likely that anything 'after' 3 also won't be working?

Likely 3 would not be working either.
With one wire in and one wire out, it is possible (though not likely) that just the out one has broken or come loose.

From the fact we have no lights working (based on the above understanding being correct) - I assume our fault is the MCB or the first light in the circuit

Yes.

There will of course be cables to switches complicating that but you get the idea.

 

[azibux1]

Likely 3 would not be working either.
With one wire in and one wire out, it is possible (though not likely) that just the out one has broken or come loose.


Yes.

View attachment 121111

There will of course be cables to switches complicating that but you get the idea.

Sounds good

Thanks for the helpful responses! Will help out a lot when I check it out later on

 

[azibux1]

Electrician said the MCB is fine (and it is tripping OK)

Means the fault is likely on the live / neutral or the switched live.

But it is a bit difficult to tell if the bathroom pull string light is on or off - so I think I'm correct in saying if we switch all other switches off and disconnect the pull string switch and replace with a connection block and test again - if it doesn't trip then we've narrowed the fault down to being on one of the switched live sides... Most likely the bathroom transformers (logically) as that is what started flashing first before the issue

Correct?

EDIT: Obviously that's wrong. I should have said leave the pull string switch disconnected to leave that circuit open (off) - ignore the connection block bit

 

[333rocky333]

are you now saying the mcb has tripped.
just click pullcord once then see if it resets

 

[EFLImpudence]

You said nothing had tripped.

Electrician said the MCB is fine (and it is tripping OK)

MCBs can't be tested (safely); Do you mean RCCB or have you RCBOs?

Means the fault is likely on the live / neutral or the switched live.

No, A fault on the switched live would only affect the light(s) controlled by the switch.
The fault will be at the light - unless the supply cable 'loops' (in and out) at the switches.

But it is a bit difficult to tell if the bathroom pull string light is on or off

It doesn't matter - if you rectify the fault, then all the other lights will work.



If things are still as in your first post, you are just looking for a disconnected or loose wire.

 

[azibux1]

are you now saying the mcb has tripped.
just click pullcord once then see if it resets

You said nothing had tripped.

Sorry, I did. It did not trip at the time of the lights flashing but I think at some point after that it tripped (or my Dad turned it off). Either way, after that also I put it on to check something - the lights still didn't work and I left it on (so did Dad) - checking it a while later it had tripped - so seems to work OK. What timeframe it is tripping in I'm unsure of, but it is not instant.

It tripped at some point also while the electrician was doing some tests - so seems functional and put to one side for now in the troubleshooting.

MCBs can't be tested (safely); Do you mean RCCB or have you RCBOs?


No, A fault on the switched live would only affect the light(s) controlled by the switch.
The fault will be at the light - unless the supply cable 'loops' (in and out) at the switches.


It doesn't matter - if you rectify the fault, then all the other lights will work.

Having a look on Google the ones you mentioned both have test switches / buttons? The 'breaker' in question does not have anything other than the toggle / trip switch - I believe it is an MCB

When I say it is fine - This is because it is tripping - If it was faulty it would not trip at all surely? See above regarding the trip.

Sorry that was badly worded regarding the switched live - I was trying to say that if all the switches are off (open circuits) and the MCB is no longer tripping then that narrows down the issue somewhat. I see what you are saying though with regards to the other lights - with the MCB in the OK position - even if only momentarily the other lights should be working regardless until it trips.

 

[azibux1]

No easy way to work out which is the first light in the circuit?

The electrician mentioned a test (from my Dad's explanation I assume this was possibly a continuity test) - but he didn't have time to do it today. So I guess there is maybe an easy way to identify the first light, but it isn't necessarily quick.