UK Identifying live, neutral and earth in outdoor festoon lighting

Richard Cook · Jun 4, 2024

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?

Richard Cook · Jun 5, 2024

westward10 said:
You can try it.

Thanks for the help, by the way.

What’s strange though is when I connect an end to the power supply the lights don’t come on. But technically they should as they come in 5m lengths. I’m wondering if the unknown wire was connected to a pin to complete a circuit within each length? If so would you reckon that wire would’ve been connected to neutral or live? I’m worried about connecting them wrong to even test.

littlespark · Jun 5, 2024

its looking like the two strings of lights come from two different sets.... the pattern of pins are completely different.

what does the other gold label say?

Richard Cook · Jun 5, 2024

littlespark said:
its looking like the two strings of lights come from two different sets.... the pattern of pins are completely different.

what does the other gold label say?

No it’s all from the same set and they’re all the same. Three rubber wires going into either a male or female 2 pin connector.

KungFuTurkeyLeg · Jun 5, 2024

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.

Is the the top pin made of plastic or metal? This is the earth pin. If it's plastic there is no earth wire down that cable.

KungFuTurkeyLeg · Jun 5, 2024

Those LEDs will have a bridge rectifier in them if they are 230v. If you reverse the polarity they won't turn on. And depending on how much chineseium was used in the manufacturing, they could already be cooked.

Richard Cook · Jun 5, 2024

KungFuTurkeyLeg said:
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.

Richard Cook · Jun 5, 2024

I found the following online but I honestly have no clue... I just wanted to fix the festoon lighting

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.

Avo Mk8 · Jun 5, 2024

KungFuTurkeyLeg said:
Those LEDs will have a bridge rectifier in them if they are 230v. If you reverse the polarity they won't turn on.

That's not correct. If you're assuming DC, if they had a bridge rectifier in them, they would work. With a single diode, not!
In any event I believe this festoon kit is all AC mains.

KungFuTurkeyLeg · Jun 5, 2024

Richard Cook said:
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

Richard Cook · Jun 5, 2024

Avo Mk8 said:
In any event I believe this festoon kit is all AC mains.

Yep these are AC mains

Richard Cook · Jun 5, 2024

KungFuTurkeyLeg said:
I mean the plug pins that go into the wall, not the end connector

Ah that's part of a "starter" cable which has a plug (that goes into the wall) and a female 2 pin connector. And yep the top pin is plastic!

Richard Cook · Jun 5, 2024

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…

Richard Cook · Jun 6, 2024

Anyone else? I’m stumped.

Richard Cook · Jun 6, 2024

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?

littlespark · Jun 6, 2024

Richard Cook said:
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

Richard Cook · Jun 6, 2024

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.

Avo Mk8 · Jun 6, 2024

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.

[ElectriciansForums.net] Identifying live, neutral and earth in outdoor festoon lighting

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!

Richard Cook · Jun 9, 2024

This was inside the “starter plug”. Is this a transformer?

Avo Mk8 · Jun 9, 2024

Richard Cook said:
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!

Richard Cook · Jun 9, 2024

Avo Mk8 said:
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?

Avo Mk8 · Jun 10, 2024

Question: did you establish the working state of the strings using the starter lead before you presumably dismantled it, or have you done this check since by feeding mains directly to the string?

My opinion is that you should use a (new?) starter cable with the rectifier incorporated in order for it to work properly and avoid bulbs failing.

I think your multimeter has already told you which is the pair of wires that go 'straight through' from plug to socket, so you should be able to work out which way round that pair need to be to mimic the other working strings. That just leaves the single (series of bulbs) string to be attached to the correct side, which could be done by trying each way.

Two wires into pin 1 (or 2 if you so determine), and one wire into pin 2 (or 1 as you determine) will be the same for all strings. You just need to work out which way round it is!

Richard Cook · Jun 10, 2024

Avo Mk8 said:
Question: did you establish the working state of the strings using the starter lead before you presumably dismantled it, or have you done this check since by feeding mains directly to the string?

Yeah I managed to establish either one all but one string working or two strings but not the rest working before the starter lead tripped the RCD and presumingly knackered the bridge rectifier which is why I dismantled one of them. It tripped the RCD as I was changing the order of the cables and stupidly connected two wires together that stopped the bridge rectifier from working. I thought I'd check to see if feeding it directly into the mains worked but it didn't so a starter cable is required.

I've ordered two new starter cables but I'm also curious that if I was to buy a pack of bridge rectifiers to fix the old starter leads which ampage I'd need. The writing on the one here has rubbed off a bit but looks like SEP do a GBU one but voltage and ampage different between models. Any thoughts?

Avo Mk8 said:
Two wires into pin 1 (or 2 if you so determine), and one wire into pin 2 (or 1 as you determine) will be the same for all strings. You just need to work out which way round it is!

Thanks so much for the help... I can sense we're super close! Yep so 2 into one pin and one into the other pin... I'll report back on my findings once the starter cables arrive, or I fix the other ones with a replacement bridge rectifier before the new leads come.

Avo Mk8 · Jun 10, 2024

I would favour using the OEM starter cable over a home repaired one, from a risk point of view (fire, electrical safety etc.)

If your string is the same as the one on the festoonlighting.com website, there are apparently 6 LED's in each bulb, and since the forward voltage of a white LED is around 3.5V, maybe slightly more, each bulb will have about 6 x 3.5 = 21V across it, so the whole string of 10 bulbs needs 210V or more to light up - the "bulbs in series" theory seems likely.
What I don't know is the current. Whatever it is, you would need to multiply it by the number of strings you are driving (plus a bit for de-rating) to arrive at the minimum current rating for a bridge rectifier.
The peak value of mains is about 340V, so the rectifier also needs to have a voltage rating well above that.

Do be careful!

westward10 · Jun 10, 2024

This is getting difficult for people from afar to give safe advice. You have now shot to pieces a bridge rectifier which you are considering replacing which is entirely your perogative but to give advice on what part you require is not sensible from our perspective.

Richard Cook · Jun 10, 2024

Avo Mk8 said:
I would favour using the OEM starter cable over a home repaired one, from a risk point of view (fire, electrical safety etc.)

If your string is the same as the one on the festoonlighting.com website, there are apparently 6 LED's in each bulb, and since the forward voltage of a white LED is around 3.5V, maybe slightly more, each bulb will have about 6 x 3.5 = 21V across it, so the whole string of 10 bulbs needs 210V or more to light up - the "bulbs in series" theory seems likely.
What I don't know is the current. Whatever it is, you would need to multiply it by the number of strings you are driving (plus a bit for de-rating) to arrive at the minimum current rating for a bridge rectifier.
The peak value of mains is about 340V, so the rectifier also needs to have a voltage rating well above that.

Do be careful!