Earth Leakage Current

Isolate the faulty equipment immediately and call in a qualified Electrician to chase out the fault. Do it before someone gets hurt/killed. Keep records of all the testing.

...because it looks like there is a connection between earth and neutral on the single phase stuff connected to Z, but I can't see it from here.

Why there is no RCCD on the single phase stuff is a mystery.

My vote's on the improperly connected/broken neutral. I've seen this sort of thing before. When the three phase load is nearly perfectly equal, no problem. Add a small amount of lighting to one of the phases and the fun begins.

Clearly you have an installation that doesn't comply with British Standard 7671!

Usually people include a schematic of the problem. If you check both ends of the cable and draw it out, the mistake should be clear enough. Without the drawing, we can only guess. It is possible to run some things while connected improperly. That is why it is important to use a properly trained electrician.

In the USA, the electrical code was written by the Fire Department. That is simply because they got tired of putting out fires caused by people who didn't understand why getting it right is so important.

You have a short somewhere. Find it, and lengthen it!

Seriously, hire an electrician. The fact that you have come to an anonymous forum for help says a lot.

If your house was on fire, would you ask the forum how to put it out?

LOL!!

Are lines of 3 phase nowadays switch individually & independently at different times- How is it possible for split phase?

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I never liked the term "split-phase" where the grounded conductor is connected to the center-tap of the transformer to provide line-to-line at (usually) 240V and line to 'neutral' at 120V. That is how most homes here in the U.S. are wired at the service entrance. I myself prefer the term, 'single phase, center-tapped'. That is because here in the U.S. we have branch circuits dedicated for heating/cooling, domestic hot water, cooking ranges, electric dryers, and other 240V loads like welders, compressors, etc. that are wired line-to-line. The rest of our branch circuits are 120V and they are wired line to 'neutral', but you probably already know that. I've never seen the term 'split-phase' in the NFPA 70 which is also known as the NEC for electrical code here in the U.S.

Two-phase in regard to home wiring is just flat out wrong. Two-phase is an arcane power delivery (five wires) designed to allow for simple motors that were self-starting. I can't imagine that there is much two-phase industry left.

Good explanation. Many thanks.

I actually did know how it worked, but thats not a problem either way for me.

I was simply not understanding what Noudge79 was trying to say....it made no real sense to me with respect to the blog....

Did you understand better what Noudge79 was trying to say?

Please explain to me if you did, and thanks in advance for your help, but no problem if you are unsure too...

No, not a clue.

I feel that we were probably not alone.....

Then its up to Noudge79 to properly explain what he was trying to say......it was otherwise a waste of a post!!

try to change your lighting connection,instead connect it before the 3 starters of your electric motor. if the problem still exist check your grounding system..