Help please with 3 phase supply into building Kva requirements

[dogwind]

Hi i am struggling with working out a 3 phase supply into a domestic building, the customer dosent want an oil boiler for heating, the electrical demands will be single phase 40A electric heating boiler (not heat pump) also instant water heater 40A plus electric shower 40A all instantaneous so no diversity then the usual requirements ie electric cooker lighting and 1 ring socket circuit (its only a small single story barn type conversion) the problem i am having is the client may also install a 3 phase electric bronze melting furnace at a later stage which i have been told is 20A 14Kva, i have got to tell the electrical supplier what size supply i need in Kva, when i add my demand its coming out around 40Kva total, does this sound about right as i have never requested a supply from scratch before myself.

Any help would be appreciated and thanks for looking.

 

[Rockingit]

The problem will come less in the maths and more in the money!! If you've a customer that MAY do something in the future, as earnest as forward planning is, the supplier may charge a hefty premium for laying in a larger supply. Assuming that your 40KvA is an overall value that's 'only' 160-170 Amps, so therefore 'only' a 63/3 supply. You probably don't want to get into installing 3ph as a domestic circuit solution as you end up having to deal with the separation etc, so that makes you lean very heavy onto one phase, which the supplier will also grumble about. It MAY make more sense to request a slightly larger than normal supply now, and IF the client installs something else later then get an upgrade or separate supply at that time.

If it's a barn conversion in the sticks, then you may only have 1ph to your nearest pole anyway - worth putting the wellies on to check!

 

[Knobhead]

With the water heating, shower and the furnace you’ve got 41.4KVA. Then add the rest of the domestic stuff at the relevant diversity.
Take in to account you will have to balance the loads and you don’t really want 400V in a domestic environment. Also take in to account the standard ratings for the service head, you could get away with an 80A 3Ph, which is 55KVA.

Have fun :angry_smile:

 

[dogwind]

hi thanks for your quick reply Rockingit a 3 phase supply runs past the barn and also feeds their house nearby,i would of taken a feed off the house supply which is 3 phase but due to it being a large house which is heated with many storage heaters which also have built in instant heaters i am unable to use this as could overload the house supply fuses, as for the cost of installing a new supply the customer is fine with that part of it, having looked on the central neworks load calculator a 43 kva would be 60A per phase, a 50kva works out at 70A per phase. I have tried to talk the customer out of having 3 phase and not to use only electric to heat the barn, its going to be more of a private art studio with kitchen area than a permanent dwelling.

Thank you

 

[dogwind]

thanks for your help Tony, sometimes customers can be a right pain especialy when they dont even know for sure themselves what they want or are going to do with the building