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?

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!

Thanks again. The website is actually ConnectPro® Festoon Lights, Connectable, SMD LEDs, Frosted Bulbs, Black Rubber Cable - https://www.festive-lights.com/connectpro-festoon-lights-connectable-warm-white-smd-leds-frosted-bulbs-rubber-cable if that makes any difference? I asked customer support and got this back…

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

"There are 7 LEDs housed within each of the frosted bulb caps..."

Richard Cook · Jun 10, 2024

westward10 said:
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.

I understand, @westward10 – didn't mean to create any issues I'm only really wanting to get these strings working and then I can rest easy. I won't be using the rewired strings permanently now... I'm just curious.

Richard Cook · Jun 10, 2024

1. Current per LED: 20mA (0.02A).
2. Current per Bulb: Since each bulb has 7 LEDs in parallel, the current for each bulb is:

0.02A \times 7 = 0.14A

3. Total Current for 10 Bulbs:

0.14A \times 10 = 1.4A

So a bridge rectifier of at least 400v with a current rating of at least 2A?

mainline · Jun 10, 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. And depending on how much chineseium was used in the manufacturing, they could already be cooked.

Using a bridge rectifier it wouldn’t matter if you reversed polarity either with ac or dc on its input.

Using ac on its input will create a rise in the dc voltage

Avo Mk8 · Jun 10, 2024

Richard Cook said:
1. Current per LED: 20mA (0.02A).
2. Current per Bulb: Since each bulb has 7 LEDs in parallel, the current for each bulb is:

0.02A \times 7 = 0.14A

3. Total Current for 10 Bulbs:

0.14A \times 10 = 1.4A

So a bridge rectifier of at least 400v with a current rating of at least 2A?

I believe it's established that the LED's are all in series. The fact that there are 7 in each bulb makes the bulbs 7x3.5=24.5V each, so the 10 bulbs in each string are using the 245V(!) mains directly from the bridge rectifier.
Each string is a series circuit using 20mA, you add these together to the give total current your rectifier will supply, your 5 strings 0.1A
However a rectifier rated at the magnitude of current you mention (1 or 2A) is more robust, and cheap enough.

mainline · Jun 10, 2024

The + and - from the rectifier will go directly to the socket for the next string.

Tagged onto the + will be the resistor and leds for that string, hence you get 3 wires but only 2 pins.

davesparks · Jun 10, 2024

Richard Cook said:
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.

An RCD is a device designed to save your life should a potentially lethal fault occur. The fact the RCD has tripped multiple times during your experimentations is a clear warning sign.

I fully support your desire to learn about how LEDs work but please do it in a safer manner, you can get a breadboard, bench power supply, LEDs and all manner of electronic components cheaply online and experiment at a safe, low voltage. There are plenty of websites,you tube videos and books out there that you can learn from.

Richard Cook · Jun 10, 2024

mainline said:
The + and - from the rectifier will go directly to the socket for the next string.

Tagged onto the + will be the resistor and leds for that string, hence you get 3 wires but only 2 pins.

So what's the best way to determining which wires go together?

Avo Mk8 · Jun 10, 2024

mainline said:
The + and - from the rectifier will go directly to the socket for the next string.

Tagged onto the + will be the resistor and leds for that string, hence you get 3 wires but only 2 pins.View attachment 116843

Exactly that.
Except in the first string of lights there are 70 diodes and no resistor (and probably none needed)
And there is/was a CN0 between the bridge rectifier and R1 (two pins from the bridge rectifier, two mating pins but three wires to that connector on the right - as I understand, neither connectors now present)
Since the connectors have come apart, the OP wants to know, holding the ends of the two wires on the left, and the three wires on the right, which one goes where!
As above - What suggest you?

mainline · Jun 11, 2024

Avo Mk8 said:
Exactly that.
Except in the first string of lights there are 70 diodes and no resistor (and probably none needed)
And there is/was a CN0 between the bridge rectifier and R1 (two pins from the bridge rectifier, two mating pins but three wires to that connector on the right - as I understand, neither connectors now present)
Since the connectors have come apart, the OP wants to know, holding the ends of the two wires on the left, and the three wires on the right, which one goes where!
As above - What suggest you?

I suggest throwing it in the bin and get a decent low voltage transformer type.

Richard Cook · Jun 11, 2024

Hi folks... thanks again to everyone who has given advice – I'm almost there. Back to the original question.

I now have a set up of:

starter cable
first run of lights (end not plugged into starter cable has 2 pin female connector removed revealing the 3 wires)
second run of lights (2 pin male connector at one end removed revealing the 3 wires connecting to the 3 wires of the previous run)
third run (no connectors removed)
fourth run (no connectors removed)

The main focus is the first run of lights (3 exposed wires at one end) connecting to second run of lights (3 exposed wires at one end).

What we have concluded is that one wire is +ve, one wire is -ve and then the third wire going to +ve also – let me know if this is incorrect.

See attached photos. I'm pretty sure I have the correct wires together on the first run (two wires connected together and one by itself). Now I connect the second run. I'm less positive about which wire is what on the second run but I manage to have the following setup:

1. First run and second run light up but third and fourth run do not
2. First run lights up, rest do not
2. First run lights up, second run does not, third and fourth do light up

I only have 3 wires so feel like I have exhausted all routes unless my first run is wrong?

1.