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So after what I thought was a productive day yesterday replacing old lights with LED panels, 3 of them weren't working. Turns out the voltage between line and neutral was about 210 at each of the 3 points, 245 between line and cpc. Voltage was 245 between line and neutral at all other points on the circuit.

I'm testing it coming Monday, but just racking my brain about it. The only thing I can think of is an insulation breakdown somewhere, either cables or in the click connectors. First test is naturally going to be IR, but thought I'd ask to see if anyone had any other ideas too so I can try it all Monday. Don't mind a bit of fault finding but man do I not have time for it at the moment.
 
Why can't it be insulation degraded dropping some voltage across like a resistor? I've checked all connections (3 click connectors where the lights aren't working and also the next light upstream) - all seem solid. On Monday I was going to remove connections from all the clicks and reterminate temporarily in wagos to test again.
 
Poor joint in cable or at a fitting would be by best guess, put a temporary cable from 1 st not working to last working light.
210v would be enough to start most led lamps, if there is a break in the cable then that voltage could just be tracking across a cable break or bad joint.
Voltage could be dropping to near zero for short durations when the driver tries to start.
 
If these are the end of a line then the issue lies at the point of failure may be worth disconecting the drivers for each of the low voltage pannels form mains and testing the voltages.

Think its going to be fairly simple find with a fresh head on monday.
 
Why can't it be insulation degraded dropping some voltage across like a resistor? I've checked all connections (3 click connectors where the lights aren't working and also the next light upstream) - all seem solid. On Monday I was going to remove connections from all the clicks and reterminate temporarily in wagos to test again.
you mean like leakage N-E? i would have thought that that would trip RCD (assuming there is one on the circuit).
 
No RCD tel, but why can't current leak line to neutral through a breakdown in insulation. Not a dead short, but enough to drop voltage across?

All lights that weren't working were disconnected for testing the voltage. Think my plan is quick IR test, then after that I'm just going to rewire it as haven't got time to be messing about
 
try dissing the first non-working light, but leaving the other 2 connected. could be a faulty fitting. I had 2 out of 24 duff out of the box on a recent job. 1 went pop on connecting, and the other flickerd on when hit with a large screwdriver handle ( an old trick from when TVs had valves inside. )
 
it's an intriguing one. let us know the outcome once you get it sorted.
 
No RCD tel, but why can't current leak line to neutral through a breakdown in insulation. Not a dead short, but enough to drop voltage across?

Because it would have tripped the MCB. Suppose the circuit has R1+Rn of one ohm (pure guess but close enough for the explanation) that R1=Rn, Zdb is low and that the faulty insulation is concentrated in one area near the end. The difference between voltages L-N and L-E was 245-210 = 35 volts, which would have to be the voltage drop across Rn between the DB and the fault. The current through the fault would be 35/0.5 = 70 amps. If it hadn't tripped the MCB for whatever reason (e.g. the circuit was wrongly connected to a 63A MCB) the heat dissipated would be 70 x 210 = 14.7kW which would rapidly start a fire. You can't dissipate the heat of twelve 2-slice toasters at a fault without it getting, er, toasted. Since a further 35V would also be dropped across R1, the supply would have to be 245+35 = 280V which would be causing other problems elsewhere. FWIW the 'insulation' resistance would be 210/70 = 3 ohms, pretty close to what one would legitimately call a dead short.

All lights that weren't working were disconnected for testing the voltage

This is key. With the lights connected, the voltage would probably have collapsed to a much lower level. The neutral is almost certainly open-circuit at a terminal and what you are reading is more or less a ghost voltage.
 
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From this I take it that it is a conduit installation? If so it is most unlikely that the faulty connection is hidden... just open the boxes until you find it, and remake it. I doubt you will have to draw in new cable unless there is extensive physical damage.
 
It's in lighting trunking, but I've inspected and reterminated all 4 click connectors. I'll get the wander lead out on Monday and test for continuity. I wouldn't mind rewiring it anyway because from what I could tell quickly on Friday, the line goes from light 3 to 4 to 5 to 6, but the neutral, as far as I can tell goes 3 to 6 to 5 to 4
 
Agree it's not ideal to have L & N visiting points in random order. This anomaly hints at a known existing disconnect between points 3 & 4.

Fun fact... Historically, long incandescent lighting circuits run in singles, particularly for display and signage work, often had the line and neutral run in opposite directions to spread the voltage drop more evenly amongst the points. The overall power loss is the same but the lamps receive more uniform voltage and therefore one end of the sign is not visibly dimmer than the other.
 
This is a big old assembly Hall with 30 lights, it would have been wired around 40 years ago so that is really useful information - I wonder if that was their thinking at the time, however I haven't investigated 1 and 2 to see what order they are in.
 
Actually, now I think about it, when I first fitted the lights and powered on the 6th light (which is 4th in line confusingly on the neutral order) was flickering ever so dimly.... It stopped flickering after I did a bit of pulling about so i wonder if my actions have made the final break. The trouble is, this Hall had so many lights out I'm not sure which were working and which weren't before I started work
 

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