3 phase neutral to earth 230v.

Need some experience on this please. I'm a maintenance engineer in a food factory. Our site services engineer asked me to check a cable as he got an electric shock from it.
Mains switchroom with 4 incoming transformer supplies. He isolated a supply feeding a compressor to remove cable as was to supply a new bit of kit. When he unbolted the old cables he didnt get a shock, panel was switched off and he checked for dead. When he pulled the cables out of panel, the neutral got jammed so he pushed the cable lug and got a belt. When he asked me to check, I checked line to line 0v, phase voltage again 0v. Cables were just dangling in the isolated cabinet. I checked the neutral to earth voltage and got 230v. Which is why he got zapped. We went to the other end of the cable, next room in switchroom and turned off the isolator, again 230v neutral to earth. I took out the neutral link out from this end, so both ends of supply cable now isolated from anything else. 0v neutral to earth. So mains incomer cable ok. Connected test meter to machine neutral otherside of neutral link and 230v to earth. So neutral is getting a 230v from somewhere. This is where I'm stuck as not my area of expertise. Not going to be my job to rectify as its not my work department. Any ideas on what is causing this issue. The 4 incoming transformers are in a locked area on otherside of incoming switchroom. These then feed other areas of factory distribution. Would a transformer neutral to earth connection cause this fault. How is an isolated 3 phase machine getting 230v neutral to earth? Tia

What type of meter give you this reading, can you be certain it was actually 230volt, you can often get some voltage N to E though not usually high readings.

Fluke multimeter

A single phase load is connected between the neutral on the 'isolated' machine and a phase from a different circuit.

Yes I’d agree with flameport. Definitely sounds like a borrowed neutral. Are you isolating the circuit with a 4 pole isolator? Have a look around and see if there are any other pieces of kit which stop working when you isolate your supply.

I had this a few years ago in an old mill. The lift supply was a straight 3 phase 3 wire supply. At some point a single phase light was added in to the lift car and the neutral was stolen from the local lighting circuit on the top floor of the mill.

If you threw the DP isolator on the single phase board everything on the top floor would stop working and appear dead but it was in fact all still live due to the backfeed from the lift light. It’s quite a dangerous situation and could have been easily avoided by someone who actually understood what they were doing.

As said borrowed neutral, the problem is when the neutral is isolated, while the neutral is connected there is no voltage, so when proving for dead one would also need to use a clamp-on meter, and even then unless what ever has borrowed the neutral is running you would not find it.

The fault can be really hard to find, assuming 30 mA is limit to what the human body can stand this means over a 7 watt load can kill. So could be a single light, it also means the clamp-on meter needs to measure down to 30 mA and mine starts at 100 mA, in the days of tungsten bulbs it was unlikely one would get a load of less than 23 watt, so even a 40 watt bulb would show, today the 12 watt LED is common so a 50 mA load so half what my meter will measure.

Yes a borrowed Neutral is the most likely cause

Appears to me the isolator had a Neutral Link in it so i assume it does not switch any Neutral.
Op appears to me to say, after the shock and only then using that Isolator and removing said link that he then also got the voltage only on the SUPPLY side Neutral of that Isolator, with the load Neutral disconnected, so as that Neutral point was never isolated from the INCOMING supply Neutral, even a borrowed Neutral could not produce 230V at that Neutral point to earth.

Initially I thought the panel switch had maybe been 4 pole and part of the panel load was connected between Live side L and Loadside N, but even that could not produce a voltage at the supply side of the Isolater with the load cable isolated surely.

To be fair i got a bit lost with the description, where the voltage was measured, maybe a drawing would help

Thanks for the responses. Got into work yesterday to be told the cooling tower wasnt working. This was fed via the panel that was having the cable removed in the roof void hidden up. Someone had nicked the neutral from this to feed something else, so twas a borrowed neutral as you suspected. Thanks again for your help.