Lighting circuit advice please!!!

[2nd Life]

Hello all.

So I am sure the expertise on this forum will be able to decode this very easily. But it has completely baffled me. I'm in training so forgive the ignorance.

Doing a bit of dead testing on a lighting circuit downstairs. Came across this at a light fitting.

Appears that the colours are cross polarity which I can deal with, But then the arrangement of these conductors feeding this fitting makes no sense to me at all. Any, advice welcome!!

In addition, at another light fitting on the same circuit I got an Rn of 0.58 back to the board, no R1, and 42 ohms line to neutral at the fitting. Haven't got clue. Help please pic attached

Thanks a lot

ý

 

[Mikegh]

The 3 reds is a looped/switch feed

They've used a red/black for the switch drop

 

[westward10]

Did you have the switch on?

 

[littlespark]

If you search online for “loop in” or “3 plate” wiring, you should see this.

Well done for doing this as “dead” testing…. Many novices or diy think, switch off, light is off…. But they don’t realise the bunch of reds are still live.

42ohms live to neutral is most definitely a lamp in circuit.

Take care of you’re zapping 500v with an MFT across L and N…. It will damage anything electronic such as LED lamps, dimmer switches, smoke detectors, extract fans…..

 

[2nd Life]

The 3 reds is a looped/switch feed

They've used a red/black for the switch drop

Thanks Mike, makes perfect sense I think with the cross colours at the fitting and the lack of a traditional rose it just threw me but really appreciate the help mate.

 

[2nd Life]

Did you have the switch on?

You mean for the R1 reading?

 

[2nd Life]

If you search online for “loop in” or “3 plate” wiring, you should see this.

Well done for doing this as “dead” testing…. Many novices or diy think, switch off, light is off…. But they don’t realise the bunch of reds are still live.

42ohms live to neutral is most definitely a lamp in circuit.

Take care of you’re zapping 500v with an MFT across L and N…. It will damage anything electronic such as LED lamps, dimmer switches, smoke detectors, extract fans…..

Thanks LS! I am familiar with 3 plate roses though usually end of line, never seen a mid run 3 plate in choc blocks so just unfamiliar territory but drew it out and now I feel a bit stupid for not seeing it! I'm aware of the permanent lines in lighting circuits so always isolate.

Would you mind expanding on the 42ohms reading LN? It wasn't from an IR test BTW. I know loads in circuit can ruin IR testing. It was a continuity test at a fitting so makes no sense to me how this would be possible.

Thanks so much for the help

 

[westward10]

You mean for the R1 reading?

Yes. How are you testing, using a long lead?

 

[2nd Life]

Yes. How are you testing, using a long lead?

Yeah using a wander lead with the conductor out of the breaker at the board end. The circuit was functional so perhaps I just missed an open switch yeah. I'll remember to double check in future thank you.

But the reason for moving on was the bizzare 42ohms reading on the continuity setting between L and N threw me. Id already seem polarity colour swaps elsewhere so started to just test combinations and that didn't make any sense to me.

Thanks for the help

 

[brianmoooore]

Main concern about this is that it's clearly a class 1 fitting, having a flylead from bracket to the fitting, but there's no sign of cpcs anywhere else.

 

[2nd Life]

Main concern about this is that it's clearly a class 1 fitting, having a flylead from bracket to the fitting, but there's no sign of cpcs anywhere else.

That's 100% accurate. Metal exposed parts fed by a 2 core cable with no CPC. It's getting ripped out shortly!!

 

[Dave5678]

Would you mind expanding on the 42ohms

Well you see how you’ve got a brown conductor connected to one choc block and a blue conductor connected to the other? They both go down through the same black sheath into the light fitting where they are connected together by a lamp and, judging by the shadow, maybe a fan motor too, so you’ll be measuring the resistance of whatever is connected to those two conductors.

If you measured between the permanent line (red conductors) and neutral then you will be measuring the loads in all the rooms on the circuit where you’ve left light switches on.

You also know that V = I R so when switched on whatever is connected will be pulling approximately 230/42 = 5.5A if that measurement is correct.

 

[2nd Life]

Well you see how you’ve got a brown conductor connected to one choc block and a blue conductor connected to the other? They both go down through the same black sheath into the light fitting where they are connected together by a lamp and, judging by the shadow, maybe a fan motor too, so you’ll be measuring the resistance of whatever is connected to those two conductors.

If you measured between the permanent line (red conductors) and neutral then you will be measuring the loads in all the rooms on the circuit where you’ve left light switches on.

You also know that V = I R so when switched on whatever is connected will be pulling approximately 230/42 = 5.5A if that measurement is correct.

Thanks Dave. The 42 ohms measurement was actually taken at a different light fitting in another room at the switch live and neutral of a wall light. But all the same applies there were still loads in circuit clearly.

What I wasn't expecting was any continuity between the two at all. The conductors were disconnected at the board. But, If it's passing down one through a lamp etc and back up that makes sense.

Sorry for the silly questions! . Cheers mate

 

[littlespark]

Thanks Dave. The 42 ohms measurement was actually taken at a different light fitting in another room at the switch live and neutral of a wall light. But all the same applies there were still loads in circuit clearly.

What I wasn't expecting was any continuity between the two at all. The conductors were disconnected at the board. But, If it's passing down one through a lamp etc and back up that makes sense.

Sorry for the silly questions! . Cheers mate

Live and neutral at the switch?

Was it live and switchwire?

 

[2nd Life]

Live and neutral at the switch?

Was it live and switchwire?

No live and neutral at the wall. But that would be the switch live right?