Multi Core Cable to IWB

Finding an Issue in a venue I work in,
the situation is as follows:
Patch bay of 6 circuits with 15A round pin plugs, Going through 18 core cable to a Junction Box on an IWB an distributed to 6x 15A sockets on that IWB.
6 cores used for the lives
6 cores used for the Nuturals
1 core used for the earth
3 cores used for a 13A socket used as 'hard power'
2 cores unused

Problem is,
When I use circuit 1 I get a shock from the plug of another circuit, Measured the voltage and read ~50v between nutural and Earth on each of the other 5 circuits.

The Power is coming from a Paradime Qpack dimmer. The voltage is present on the 5 other circuits no matter which of the Circuits are plugged into the dimmer, and whether the dimmer is at full or at 0.

Any suggestions on why i would be getting this voltage on all the other circuits?

It’s likely that in one of the connectors multiple pins have been bonded together. This is not uncommon as a lot of multi cable was 14 conduction with 6 hots, 6 neutrals, and 2 ground pins bonded together.

Very Euro terms above, though the 15A in normally 16A confuses me. Say 16A CeeForm outlets in example, or is it the other 2-Pin with something of a grounding ring plate I never understood? This is going thru 18 wire multi-cable to a junction box. IWB is not a familiar term. I assume some form of IWB breakout box, to six more breakout boxes?

So you have 6x circuits breaking out to 24x outlets for fixtures.

12 wires on the multi-cale used for hot/neutral, three for ground. Not sure what the "hard power" is in three wires assigned to it - 415v power? Math fuzzy.

Un-balanced load would be a often meter 50v between phases to neutral, but not if getting shocked. Mis-pinned somewhere more likely.

Otherwise I used to work in a 1911 theater in Chicago which was using a pin rail index light, using an ancient crows foot connector. Everfy time someone tried un-plug and re-plug the fixture to re-wire the fixture it electrified the grid and would even spark if one tried to use the pipes around the pin-rail to bend a pipe. I now own that Darned' fixture - museum piece and safely re-wired! None the less, it was a fixture neutral and short to ground but reverse wiring. If you plugged it in the way it always was fine... as with much of the hanging stock... it was fine. If you tried to wire it properly sparks, but no shock. Ah' the days of bronze wire rope and insulator balls between grid and pipe... Old school.

Given no shock on my part for a remote fixture causing the problem, less something to look into than the distribution boxes and cables to them - all of them.
Worrysome in seemingly a multi-cable with different voltages in it no matter where we live - should be looked into in not doing.

In the multi-cable plugs they are heat shrink insulated between conductors and no soler blobs? Inspect all. Most important questions:
What has changed since you noted this? Or the history of changes/improvements?
Inspect the outlet boxes... in good condition physically? Any charring on pins?

Where did you get shocked? Inveisigate that perhaps first given the above? Sometimes could be a bad crimp terminal which left a wire floating, or etc...

15A = BS546 round pin plugs (also used in South Africa) - very common still in UK theatres. See here for example.
IWB = internally wired bar.

Are the 15A tails going directly into trunking and thence to the IWB (as they do in our theatre) or are they part of a SOCA spider fan-in? If so, as mentioned, there could be a problem in the SOCA.

All of this that follows assumes you are a "competent person" in UK law to undertake the following tests.

I'd open up the box on the end of the IWB with all the circuits unplugged and look for obvious faults, then using an ohmmeter systematically measure the resistance from each patch plug pin to all of the others individually until you find your leak. Does sound to me like a ground/neutral short, perhaps. Also check that the Live and Neutral for plug 1 actually end up at socket 1 etc. as intended - check for "cross wiring". It shouldn't matter in theory (all neutrals go back to a common neutral eventually, likewise the earths), but cross wiring should be rectified anyway.

The fault may be in a fixture, so unplug all of those first, and test each one individually.

Perhaps less likely is a "soggy" neutral that is being pulled away from earth potential. Can you measure between the neutral and earth at the dimmer and make sure it isn't wandering?

Based on my own personal experience in 120v systems, a 50v difference to ground has always been a misbonded ground/neutral. That particular voltage always rings an alarm bell for me. I don't know if that holds true in a 230v system.

By the way, Rory, I've no idea what part of Scotland you're in, but if you ask the same question over on the (more UK based) The Blue Room, you may find their is a a member near you who could look in and help.

Blue room a great website. In trying to help, sometimes problems are two or three in lining up for a hard to figure out problem until you find it. Ah' that's the plug/connector 15a in question.... Lots of adaptors from them to other stuff in stock, but never really knew their purpose. Thanks for some areas they are used in.

Aside : It's not unknown in UK theatres, where there has historically been BS546 15A outlets for dimmed circuits, to leave them in place and run new IEC 60309 (Ceeform) for hard power. That way you can't plug an "intelligent" fixture into a dimmed circuit, because it has a different plug.

In our theatre we just use BS546 for practically everything, apart from portable dimmer packs which have 32A ceeform.