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UK Identifying live, neutral and earth in outdoor festoon lighting

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Richard Cook

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I bought some outdoor festoon lighting a few years ago and the 2 pin connectors (male and female) have corroded so I’m going to splice the connectors together using heat shrink butt connectors. Each run is 5m with a male and female 2 pin connector at each end. My first thought was that this would be a 2 min job but it turns out none of the wires are labeled so it’s tricky to work out which wires are live, neutral and earth once the connectors have been cut off.

See a few photos attached.

I can connect one end (thankfully the one end that isn’t damaged) to the “starter plug” which has a transformer (31v) so can voltage check each cable and plug it in.

At the other end, with the now exposed wires, what’s the best way to find the live, neutral and earth? I’ll then need to Wago, for testing, this to the other run but how do I work out which is live, neutral and earth on that run? Trial and error? What am I looking for? Would it trip the RCD until right? What about the transformer? Any way I can avoid breaking it with testing?
 

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You really shouldn't plug them in to measure voltage if it's kicking out 230v. With the plug pins facing you, the bottom right pin is live and the bottom left is neutral. Tap out as before and you will know what is live and neutral at the other end using resistance again. No need to risk a shock.
Isn't this just the same as measuring voltage in a plug socket? And the plug pins can face me upside too... there's only two pins. Do you mean with the key on the 2 pin connection plug at the bottom?

There's three wires going into a male 2 pin connector at one end three wires going into a female 2 pin connector at the other.
 
I found the following online but I honestly have no clue... I just wanted to fix the festoon lighting :rolleyes:
  • Parallel Wiring: Festoon lights are usually wired in parallel, meaning each bulb gets the same voltage. The third wire could be part of a parallel circuit configuration. In this case, two wires would carry the live (L) and neutral (N) connections to power the lights, and the third wire might be used for a return path or additional circuit stability.
  • Voltage Drop Reduction: In longer runs of festoon lighting, voltage drop can be an issue, leading to dimmer lights at the end of the string. A third wire could be used to mitigate this effect by providing a more stable electrical distribution along the length of the cable.
In either case checking continuity in the unknown wire would yield some results if it was connected to either pin in the moulded connector... but it doesn't.
 
Isn't this just the same as measuring voltage in a plug socket? And the plug pins can face me upside too... there's only two pins. Do you mean with the key on the 2 pin connection plug at the bottom?

There's three wires going into a male 2 pin connector at one end three wires going into a female 2 pin connector at the other.
I mean the plug pins that go into the wall, not the end connector
 
So I put one multimeter probe to one of the two wires (the ones that had continuity) and the other probe to the plug. With one wire both plug pins had continuity. The other wire had none. I’m assuming that wire is therefore the live but weird it returned a reading for both pins on the plug…
 

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Okay so I had a better look at one of the 2 pin connectors. Looks like two wires go into one pin and one the other. So I tried this temporarily. See photos attached. I’m not sure which wire is live and which is neutral on the second 5m length but I do know which wire wasn’t returning any continuity so I labelled that earth (even though it isn’t).

When I connected neutral on one length to one wire on the other length then live and the “earth” to the assumed live and “earth”
on the other the first set of lights lit up! But the other length didn’t. So I swapped the “neutral” and “live” around with the wires I wasn’t sure was and again the first set of lights lit up but the other length didn’t.

Any further thoughts?
 

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Any further thoughts?
Buy a new set?


Sorry, that wasn’t helpful… but it’s beginning to seem impossible to diagnose from here.

You’ve got two strings that don’t seem to match up… a plastic “earth” pin and double insulation symbol that suggests you only need 2 wires, but you’ve got 3….

I’m afraid you may be powering this up just to see what’s working, and risking serious injury to yourself
 
Haha I understand but these were expensive and IP65 rated but only 2 years warranty so I’m determined! Can’t be that hard! 🤪

I connected all the other lights and seems like it may be just this one set of lights not turning on. 5 x 5m lengths.
 
Looking at a website advertising these 240V lights, it seems to me that the particular set you have is unusual in having 3 wires between each bulb in the string of 10, but having two pins on the connectors.
They say the bulbs are not replaceable.
I'm just wondering if the LED bulbs themselves are each 24 volt and all in series as below, which would account for the 3 wires between the lamps, and why two are joined in the connector.

IMG_0577.jpeg

If you've managed to get the corroded string working, I can't fathom why further strings plugged into that don't work.
Do all the other strings plugged into the starter lead work?

I would say it doesn't matter which is L and N, they are interchangeable. It does matter where the 3rd wire goes, and it's not E!
 
This was inside the “starter plug”. Is this a transformer?
It's a bridge rectifier made by SEP. Incoming mains wired to the central 2 pins, and then DC + and - from the outer pins. Gives a DC supply for the LED bulbs. So it does matter which wire is +ve and which is -ve!
I wondered what the lump in the starter lead was for!
 
It's a bridge rectifier made by SEP. Incoming mains wired to the central 2 pins, and then DC + and - from the outer pins. Gives a DC supply for the LED bulbs. So it does matter which wire is +ve and which is -ve!
I wondered what the lump in the starter lead was for!

Wow I feel like this is a breakthrough AND that we can figure out how to connect the 3 wires together? I’ve had the following combinations working:

1. All lights working except the second in the run which one end has the 2 pin connector cut so it’s connecting the three wires via Wagos (to test with) to the three wires (2 pin connector also cut) on the first in the run.

2. The first two runs working but the others after not

Anyway… with what we know now it looks like two wires connect together into one pin and one wire into another. Does it alternate so 2 wires into 1 and 1 wire into 2 all the way along?

The issue with that bridge rectifier is when the RCD switch on the circuit went when testing via combinations it rendered the starter cable redundant. So it’s a required thing?
 

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