shower block supply

[bro8284]

Hi Guys,
Looking for a little advise regarding installation of new supply to feed a communal shower block at a caravan site.

The shower block will have 7x 8.5Kw electric showers, 2x 2Kw over-sink instantaneous water heaters, a couple of frost guard heaters and lighting with a couple of extractors. In total i calculate the max load to be just shy of 65Kw.
25mm 4core SWA has already been run back to the supply on recommendations by another electrician.
The problem I have is what size breaker to fit at the supply end ...
Most standard load 3 phase boards only allow a maximum rating of 63A for the MCBs and I know that this will be too small for the shower block.
I've calculated the max load as everything on at the same time due to the fact that the shower block will be used during both summer / winter.
The way I see it, everybody could all turn up at once to shower/wash so I can't really justify using diversity.
Based on this, I'm thinking that the submain will need to have overload protection of over 80A.

Any help would be great,

Thanks guys ...

 

[telectrix]

in that case fit a KMF with 80A fuse. what's the earthing arrangement?

65kW eqwuates to 270A before diversity. some serious calculations needed here.

 

[bro8284]

in that case fit a KMF with 80A fuse. what's the earthing arrangement?

65kW eqwuates to 270A before diversity. some serious calculations needed here.

Thanks for the reply, the earthing i believe is PME and i agree the calculations are giving me a headache.

 

[Richard Burns]

Do not have a distribution board as your sub main protection at the supply end use a 3 phase switch fuse then move down to appropriate distribution boards for the final circuits at the shower block.

 

[telectrix]

oops. just seen the 3 phase bit. now it makes sense. ignore my last post. as richard pointed out, a 3 phase switch fuse with 80A fuses will do the job.

 

[westward10]

Hope you are not using the armour of that cable if main protective bonds are required.

 

[bro8284]

Cheers guys thats helped on that problem,
I haven't done loads of three phase so that didn't even cross my mind. much appreciated.

 

[bigspark17]

You said "i think the earthing arrangement is pme" how have you not looked at this yet, as @westward10 said if main equapotential bonding is req your headaches will be getting worse! How long is this submain?

 

[Leesparkykent]

Being a caravan park I wonder how long the SWA run is..

 

[UKMeterman]

Might be an idea to suggest to client a chat with a plumber about putting in a large unvented cylinder or two, with a solar coil and suitable immersions. Have a chat with Hot water cylinders | Indirect hot water cylinders | Gledhill cylinders | Pressurised hot water cylinders | Domestic hot water cylinders - http://www.gledhill.net for ideas, cheaper running costs, might cost a bit more on the install though.