Voltage dropped

It has to be a loose neutral.

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

I wonder if that was their thinking at the time,

Click to expand...

No, more likely it's just muddled up and spaghettified.

Okay, so there was something else happened on Friday, I didn't mention it at first because my pride was massively wounded, but I got a belt (my first, and hopefully last). It happened because I didn't isolate properly - I'd been isolating all day properly, but then towards 3pm on Friday I was getting fed up, my head was frazzled, and I only isolated at the switch, totally forgetting that light 5 had a permanent feed for an emergency fitting. Yes, stupid, and it has certainly humbled me.

Thing is, and I'm probably being thick as they come, I can't understand how I got a zap. Here's a diagram of how the wiring is, I'm not sure where light 3 comes from, whether it's from 1 or 2 as I haven't opened then part up. Lights 1 and 2 were still connected but turned off at the switch. Light 2 also has a permanent feed as that's emergency, but that's upstream on the circuit. Lights 3, 4, 5 and 6 were all disconnected fully (click adapter). As you can see, line moves 3 to 4 to 5 to 6, neutral does some fudged stuff. Anyway, switched line off, permanent line not isolated, but no loads past light 2 (as far as I can tell). I removed the neutrals at click adapter #3, and as I did my thumb bridged the gap between them and I got a belt.

So, someone please tell me I'm being stupid and that it's really obvious why seperating the neutrals on a dead circuit gave me a tingle. I know permanent line was still live at light 5 but there was no load connected to it. Likewise, permanent line was still live at light 2 but that's upstream and so that should have still had a neutral connection present.

I'm eager to get back up there and see exactly what the hell is going on, but I'm not allowed to until an LA spark comes out and signs the incident off.

Sounds like you have another circuit borrowing the neutral from this one, a circuit which is still live. Can be hazardous on lighting circuits which have crossed neutrals. You also need to isolate the permanent line, old lighting circuits can be a minefield.

westward10 said:

Sounds like you have another circuit borrowing the neutral from this one, a circuit which is still live. Can be hazardous on lighting circuits which have crossed neutrals.

Click to expand...

That was my initial thought, when it happened the first words out my mouth were "f****** lazy t**** borrowing a neutral" (yes I see the irony in calling them lazy when I didn't isolate properly). But I still can't see why that would be the case. I've got a dodgy neutral hence why lights 4, 5 and 6 aren't working, so any load behind this (borrowing the neutral) surely wouldn't work either. I will get to the bottom of it when I'm allowed back on the job, but it's driving me insane.

Your neutral issue is still showing 210v so this will still give you a belt. When you can carefully disconnect the neutral at the board and see if it is live with the protective device off.

Thinking this is an "emergency lighting" only thing ?
(If was normal lighting in off state - Bor Neutral was only way)
Seeking a charging opportunity, if they are "self sustaining".
Floating neutral will also seek out any cpc. -

Unless you had the emergency light fully disconnected then the charging circuit will have been live. Disconnecting the neutral upstream of it will cause the black wire from the emergency light to cease to be neutral and rise to line voltage.

I think HT's point was that all the lights on the affected section were unplugged from the Click fittings, so although the PL was present at the Click, there was no load, not even the EM charging load, to complete the circuit to the floating length of neutral to give him a shock w.r.t. the good section. I too would have been surprised to get a shock if all were as per his sketch.

Unfortunately we are dealing here with a section of circuit that is known to be faulty or incorrect, although we don't yet know how, where or why. So it is a leap of faith to assume that the circuit will behave in the way we expect. With luck, the cause of the shock path will be revealed at the same moment the original fault is found. Not much point guessing with so many variables.

Noting this is a big assembly hall with long cable runs perhaps this is the 'real' circuit (and you could add some insulation resistance too if you are feeling artistic(!)...) These capacitors are charged to +350V and the -350V every cycle.

Thanks all, I appreciate all the ideas being bounced around. It's out of my hands now, I'm not allowed to touch it until a council spark comes and takes a look. At the moment I feel a bit foolish, and just hope tomorrow he has the same findings as me thus far. I've really enjoyed working on electrics this past 5 years or so but this has really humbled me, and I don't know how I'll feel should something be found that i really should have spotted at first sight.

I wouldn't worry about it. The wiring doesn't sound very straightforward.