What's going on here, or rather what is not going on here?

[Birduder]

Dear Electrical Geniuses, please help me if you can.

The problem started when the LV lights in the bathroom randomly went off and then came back on when they felt like it. I read that they might be overheating and as we had our loft reinsulated not that long ago thought that might be the reason, it isn't.

Someone told me that it was the transformer, so I have changed that and that does not make any difference, in fact now, since I have got involved, the lights are permanently off.

I bought a voltmeter and at the switch in the bathroom there appears to be 142V. The feed to the transformer is showing 247V, however the feed out of the transformer to the lights' junction box is showing 0V.

I suspect I am doing something very silly (e.g. trying to do electrics) but would be grateful for any pointers please.

Thanks

Rob

 

[Spark123]

If you have 240v going into the transformer and nowt coming out then the transformer is the issue. What make and model transformer?

 

[PrenticeBoyofDerry]

I did you wire the transformer the right way round?
Just for accuracy LV=low voltage, your transformers are ELV=extra low voltage.
Transformers require ventilation, smothering then in thermal installation is a no no!

 

[Birduder]

Not sure of the makem I have to confess it is the second one I have tried because I think I knackered the first one. It's all ventilated so that is not the problem but I can't help thinking I have wired the transformer up incorrectly, but there is not much to it.

As far as I can see there is a feed (live and neutral) into the end marked 230V (in the first transformer the L and N were clearly marked, not so in the second one I am using) then at the output there are two banks of three terminals, I assume (maybe I am totally wrong) that L goes into one bank and N into another? One thing has crossed my mind, if you imagine the terminals are both numbered 123 looking left to right do you need to wire L to 1 and N to the corresponding 1? I have wired it (in my notation 3 and 1) (but I thought the terminals were all connected, perhaps not?). I am pretty sure the one I unwired in the first place was wired into the two terminals nearest to each other (so 3 and 1 as I describe).

The lack of power out does seem to suggest the transformer is bust. One other thing (not sure if significant) I am pretty sure there were 240V into the transformer irrespective of whether the switch was on (or perhaps that is right and the switch just completes the circuit?) Incidentally why is there only 142V across the switch?

Sorry to be so dumb about it and thanks for the help!

Rob

 

[PrenticeBoyofDerry]

Can upload a photo of one?
You should not be getting 240V when switch is open and if you have incorrectly wired them, the chance are you will not get a reading at the SELV side either.

 

[EFLImpudence]

Incidentally why is there only 142V across the switch?

There will be 0V when it is switched ON.

Is that why you think there is 240V (at the transformer) when the switch is 'off'?

 

[ericmark]

The transformer is likely not a simple transformer but a switch mode power supply. These have a min as well as max so if there is no load it will likely go to safe mode an switch off. So 230 in and 0 out does not mean it is US. It could be zero out either will no load or overload.

 

[skotl]

Here's a dumb question for you...

You're measuring 240V AC on the input side of the transformer. When you measure the output side, are you selecting DC on your shiny new multimeter?

 

[Birduder]

Hey that's a good question, I am pretty sure I did select DC even though I am a thicko I think it did cross my mind.

I will have to redo the measurements tomorrow and check it all but I am pretty sure the numbers I have given are correct.

The solution is clearly get an electrician in but I am kind of annoyed I cannot work it out for myself.

Regarding the switch I just assumed that I stuck one 'probe' on live and the other on the other wire.

I will come back to tomorrow with a proper set of results.

If I had posed the original question - why are my LV lights going on and off what would have been the answer I wonder? I think that is where it went wrong and my meddling has just exacerbated what was probably an easy thing to fix!

Thanks for the help appreciate that

Regards

Rob

 

[EFLImpudence]

Regarding the switch I just assumed that I stuck one 'probe' on live and the other on the other wire.

Precisely - and when the switch is ON it is the same wire.

Wires can be anything WE want them to be; they do not know what colour they are.

Measure with one probe on wire and one to earth.

There is no neutral; it is a blue wire.
A neutral is the wire which completes the circuit from the load back to the origin.

Draw the circuit.

If I had posed the original question - why are my LV lights going on and off what would have been the answer I wonder?

Loose connection somewhere or faulty transformer.

 

[PrenticeBoyofDerry]

or dodgy lampholder!

 

[Birduder]

Okay here is what I have found.

1) Switch in the bathroom has 245V across it (I was measuring the wrong things - oops) and then 0V when off, so the switch seems to be working

2) The input from the switch to the transformer is 245V

3) There is no output at all, and I definitely measured it on DC. Even if there were no lights connected should I still see a DC output at the terminals?

Something else I have discovered, not sure if it is relevant, is that in the junction box where the cables for the lights come together there is an earth wire. This wire is NOT connected to the transformer (it was not in the original one either).

On the input from the switch would it make any difference if I swapped the wires over? As I said in the original transformer it says L and N, this one (Powertran by the way) has no such markings.

Have I perhaps blown this transformer too?

What a pain, but it does seem to point towards the transformer although I don't know a way of testing that, is there a way with a multimeter?

Thanks for your replies

Rob

 

[EFLImpudence]

1) Switch in the bathroom has 245V across it (I was measuring the wrong things - oops) and then 0V when off, so the switch seems to be working

It will have 0V across it when ON.

2) The input from the switch to the transformer is 245V

As it should be.

3) There is no output at all, and I definitely measured it on DC. Even if there were no lights connected should I still see a DC output at the terminals?

Some will only output when a load is connected.

Something else I have discovered, not sure if it is relevant, is that in the junction box where the cables for the lights come together there is an earth wire. This wire is NOT connected to the transformer (it was not in the original one either).

That is likely correct. Is the transformer class 2? Are the lights class 2?

On the input from the switch would it make any difference if I swapped the wires over? As I said in the original transformer it says L and N, this one (Powertran by the way) has no such markings.

Everything I buy comes with a set of instructions.

Have I perhaps blown this transformer too?

How could we tell?

What a pain, but it does seem to point towards the transformer although I don't know a way of testing that, is there a way with a multimeter?

What have you been doing?
Wire it as it should be and put the probes on the output terminals but as said if there is no load it may not show anything.

What is the total wattage of the lights?
Does this correspond to the rating of the transformer.

Perhaps the original problem was a loose connection at the junction box and now you have dislodged it completely.

It really is not complicated.
There are two wires into the transformer and two wires out.
Then two wires into the junction box connected to two wires to the lights.

 

[Birduder]

Blimey that was a long reply, thanks.

There were instructions but they were hopeless, just showed input and output. No idea what class the lights are the transformer is Class 2. I have had another look at the instructions and it shows L and N on the drawing but I cannot see that marked on the transformer at all. The rating is the same as the one that worked for a few years.

I have no tried the transformer voltage and then switched the switch on, I will try that next.

In the junction box there are actually four lights that come into one.

I agree it is not complicated but I cannot see what is wrong unless the transformer is shot or wired incorrectly. I have checked the junction box and that all appears to be okay.

Will try (after the GP) to test with and without load

Thanks

Rob

 

[Birduder]

Right basically I have given up, I am sick to death of wiring and rewiring and getting my wife to traipse downstairs to flick the RCT.

I did check that the volts were 240V and 0V when the switch was used, that worked. I then wired up the lights again and got nothing. So then I wired up the original transformer and surprise surprise the lights came on. Even though they were on I could still not get a reading on the multimeter it was always zero (I know, I know it cannot be) the only reading was a random reading around 5-9 on AC! The lights then went out.

I wired in the first new transformer (same model as the first though the L and N were round the other way) and the lights and the RCT tripped. Unwired the lights and the trip did not go. Touching the wires to the terminals in many combinations did not do anything but did not trip the RCT. So I wired in the second new transformer, nothing but did not trip the RCT.

So basically I have wasted £35 and several hours to get nowhere. The light switch seems to work but I have no idea whether the transformers are all faulty or there is something else amiss. Checked the junction box and all the wires seems fine in there.

Anyway thanks for your help, I am sure you were entertained by this electrical numpty!

Fortunately my son's drama teacher is married to a sparky so I will call him!

Regards

Rob