UKH

This is probably a simple question that I am failing miserably to explain to Google:

UK wiring regulations, for 3 phase appliances can you use 3P + E or do you have to use 3P + N + E? I have spent the last few hours trawling the web and either this question is so blindingly obvious no one has bothered to answer it or my Google skills are truly awful. 

I have a former electrician who thinks we should be re-cabling a bit of equipment with 5 core and one who thinks 4 core is fine. 

It would depend on the equipment, eg a 3 phase motor dosen't need a neutral, so 3P & E is used.

And the ground/return system, I had a workshop (in Germany) and it was 4 wire, other side of the river it was 5. My home and workshop are 4 wire and my other workshop  it's kinda optional! The electricity board are pretty rigorous checking my ground system though, bit of water pipe whacked in the ground doesn't cut it.

As BB said, the choice of 4 core or 5 core depends on the equipment. If your electrician is proposing to re-wire a bit of 3P+E kit with 5 core, where is he planning to connect the neutral to?

Cheers, managed to find a 3rd electricity wrangler who had done a lot of installation of 3 phase equipment and got a definitive answer. Pity I only thought of asking them after I had posted this and ordered a copy of the 18th edition Guidance. 

Funnily enough that never came up in the initial conversation!

Ey up,

I'm an electrician. What's the appliance, do you have documents for it? 

Edit: cross posted with the above, see you've got it sorted.

Did you not show them your 'stake testing' page to prove it did?

This probably echoes what your 3rd spark said:

3PN+E can be wired with 4c armoured cable using the armour for earth. 5c is typically (but not exclusively) used where the earth loop impedance is too high using the armour alone. Even then a supplementary or separate cpc (earth) is commonly used because 5c cable can be relatively expensive. 

Some three phase kit doesn't require a neutral. The equipment should identify if this is the case. If so 4c or 3c + (armour and/or separate cpc) can be used. 

Ground return systems for the neutral are not recognised by BS7671 (nor I believe the German DIN equivalent). Some railway traction systems use them but they are covered by different standards. Jimtitt's 4 wire vs 5 wire observation most likely reflects the utility supply earthing system, e.g. TT vs TN-C-S vs TN-S, which is not directly applicable to the OP. It does affect the earth loop impedance requirements though so influences at what point the armour alone becomes insufficient as the cpc.