Neutral went bang - can someone explain this wiring to me?

Electrics · Sep 10, 2021

I was wiring up an IP65 5ft LED batten today, straight swap for a non-LED version.

The light was an emergency and worked off a sensor, no switch.

The emergency was wired through the test switch.

In the light fitting, there were 4 wires - brown switch live, black live, neutral and earth.

As i took the neutral out, i got a flash bang and a pop. Didn't get shocked and nothing tripped out anywhere. Guy i was working with said he didn't have time to explain it to me, but that it was because the neutral was coming from the lights in the adjacent room.

We then turned off the MCB for that room and i cracked on.

I'm a bit confused as to how this all works. Anyone explain it to me?

(Ps - i'm currently working for a company and wasn't just doing this DIY - i'm being directed by a qualified man at work.)

Vortigern · Sep 11, 2021

A sensor would have a L N and a L out to the light so you should have seen three wires, not just black and red and earth. Shame there is no pics. The light you were working on, just to be clear, there was only four wires going in to it? Not eight wires, i.e. looping to the next fitting in line???

nicebutdim · Sep 11, 2021

CamoElectric said:
This is going to really wind me up.

Don't let it - if you get the opportunity to figure it out, then well and good. If not learn what you can and add to that at each subsequent opportunity.

There's a mountain to climb and the only way to the top is one step after another.

Electrics · Sep 11, 2021

Vortigern said:
A sensor would have a L N and a L out to the light so you should have seen three wires, not just black and red and earth. Shame there is no pics. The light you were working on, just to be clear, there was only four wires going in to it? Not eight wires, i.e. looping to the next fitting in line???

The light was fed by 3 core + earth flex, one cable in, push fit connections at the fitting and black, blue, brown and earth.

I think it was the last on the circuit from the lighting in the room next door since that room was a main shop front but the light i was changing was in a store cupboard so maybe added as an afterthought. Might be why i still got a bang since the cupboard was only turned off at the keyswitch and not the MCB - when the MCB was turned off the lights in the main shop room went off.

I'll draw a pic of the set up.

Electrics · Sep 11, 2021

You know thinking about it, the wires were really short and when i took the neutral out it's possible some of the other wires touched.

I'm wondering if the line from the sensor has shorted which is why the sensor is now broken and doesn't work. It's not a coincidence imo that the sensor stopped working immediately after this.

If the sensor was still live then it's going to switch live as soon as it senses my movement in the room isn't it? Normally i think you switch off the light and then kill the emergency switch so the emergency light comes on the battery power but if it's a sensor and not a switch then you can't kill the power unless at the MCB, which was still on?

Still confused mind as to how the RCD never tripped.

westward10 · Sep 11, 2021

A flex indicates a coupler in the ceiling void.

Electrics · Sep 11, 2021

westward10 said:
A flex indicates a coupler in the ceiling void.

Coupler? You mean like a connector block or such like?

westward10 · Sep 11, 2021

CamoElectric said:
Coupler? You mean like a connector block or such like?

No some kind of luminaire coupler like a Klix socket or similar. In fact if this is the case then it makes replacement easy as you just unplug it.

Electrics · Sep 11, 2021

westward10 said:
No some kind of luminaire coupler like a Klix socket or similar. In fact if this is the case then it makes replacement easy as you just unplug it.

Yes i know exactly what you mean - i replaced several of those on the same day. Oh man that would be hilarious and maybe slightly tragic if one of those was tucked inside the ceiling panel and we didn't see it.

ipf · Sep 12, 2021

Don't worry about it......it's all done different in Essex, anyway...

You're not the first to 'em to be flummoxed.

Electrics · Sep 12, 2021

ipf said:
Don't worry about it......it's all done different in Essex, anyway...

You're not the first to 'em to be flummoxed.

Looks like there was probably stuff tucked up in the ceiling that we didn't see, whether that be a coupler or a JB or whatever. Probably easy to figure out if you have a good poke around. If i get sent back there this week i'll update with some pics.

ipf · Sep 12, 2021

An EICR lately had something similar. The light fittings, moved from original positions, were fed with a 3c flex. If you've got access or can obtain it, fair enough. If not, as in the EICR, it's dependant on the test results and, in many cases, a bit of 'hit and hope'. There's no saying what state the joints are in. Fully testing is important.