Wiring for a 15kW oven

Hello gents - I would like to hear suggestions for best practice in wiring a 3PN Lincat commercial oven, model ESLR9. L1 & L2 draw 26A/6000W each and L3 draws 14A/3200W.

There is a 3-phase supply in the shop and the owner has run 2 x (2x2.5mm2) T&E to supply 2 outlets next to the oven to power L1 & L2 (effectively 2 new ring mains, but only supplying the cooker). There is an existing ring main which he is hoping can supply L3 via an isolator.

This doesn't sound quite right to me, and I believe he ran the 2.5 because it was cheaper than running 4-core & E SWA or similar. Equally, I would've thought that there should be a single 3-phase isolator next to the oven, rather than the proposed 3 individual switches.

Also, what would be the standard way of connecting the isolator(s) to the oven itself? What cable would be used here (5-core heat-resistant?).

I am an NIC approved contractor looking to move from domestic work to light commercial work like this, but, as you can see, I need some pointers!

Many thanks

PS I know that if I don't step in and do this job right, he'll probably go ahead and get someone else to do it who is not an actual sparks

Definitely not the way to run it, having to isolate it at 3 different points is very wrong. Even ignoring the safety aspects that you might not realise it isn't fully isolated, the way he is proposing it you will have to link the neutrals of all 3 circuits together, which means that if any of the circuits are on different RCDs, they will trip out.

It should have as you say a single 3-phase isolator, that runs back to a 3-phase breaker in the CU in one cable (or singles in conduit/trunking or whatever). In terms of cable to the oven itself - that would depend on what the manufacturers instructions say - it might need heat resistant stuff, it might not...

TP B32 MCB

4 or 5C 6mm² SWA to rotary ISO.

From ISO to oven in some kind of heat resistant flexible cable, either direct ot via a socket/plug

Thanks, all very helpful. This concurs with my thinking that this needs to be wired on a more industrial level, with possibly trunking or tray and either 6mm singles or SWA. I guess a Ceeform socket outlet after a rotary isolator would be useful, then flexible cable with a plug to the cooker.
The TPN distribution board is also dodgy, with a large gap where there are missing MCB blanks. I'm pretty sure you could get most of your hand in there... (I've since temporarily covered it). So that needs to be sorted.
All in all, I don't think the owner would be pleased to scrap his T&E and mini-trunking plus surface accessory boxes and then be faced with a large bill for doing it the right way! I haven't actually met him yet, but if/when I do, I'll do my best to convince him of his obligations regarding employee safety, etc.

I get the feeling, though, that he'll get someone else to do it his way...

Are the circuits he's put in protected by RCDs/RCBOs, as if so, and they're not all protected by the same one, then if he does get someone else to do it 'his way', you can just sit back and laugh when it all trips out on him, and he has to do it properly anyway...

If he does get someone else to do it, and you have reason to believe they're doing it this way, I'd personally contact the HSE - they probably won't do anything about it, but at least you've tried (and your conscience would be clear if anybody does get injured by it in the future)...

No RCDs, RCBOs at all - just a couple of MCBs, one for the shop power and one for lights. Didn't look at the earthing (as I should've!) but there's probably no main bonding.

I think I'll meet with him and spell it out, though he'll probably just think I'm the electrical police...

I'd run it in 6mm, either SWA or in conduit feeding to a 32A 5pin ceeform socket with isolator from a 3phase B32 MCB. Probably get away with 6mm 5c HO7RNF from the plug to the oven unless the manufacturer specifies something else.

No way would I use his method - there is what sounds like a shared neutral between 2 circuits for starters.

Thanks spark123, that sounds like a good plan. I guess I can expect a 3-phase MCB to fit a standard TPN db in that it straddles all 3 phases and has just a single breaker switch?

The shop owner is clearly the kind of DIY guy we've all come across who reckons if he can figure out how to make it work, then that's good enough. He's expecting someone (not me!) just to wire his T&E into the board at one end and then into the cooker at the other. Job done for £50!

3 phase MCBs just look like 3 single phase ones joined together, the levers joined with a bar so they are all closed at the same time. They are also linked internally too so they all 3 phases trip at the same time.
If he really is a cheapskate with no regards for electrical safety then run a mile!

Run forest run......