How far can reality be allowed in diversity?

[Richard Burns]

Similar to the two showers thread, sorry.
I have been asked to supply a sauna (4.5kW) and electric shower (7.5kw) lights and sockets (using an oil filled radiator) to an outside room.
The supply is TNS, 80A (presumed) and the existing split board has 3 RFC, 3 light circuits, 1 immersion heater, 1 UFH (200W? on16A), 1 40A cooker (induction hob and separate cooker).
Diversity calculations on the existing give about 160A (OSG), 80A, (0.4*mcb), 60A (rationalising circuits for a 2 bed terrace), 20A measured load (cooker, washing machine, PC, TV,lights on).
Theoretical load from new room, if everything turned on, about 55-60A.

I believe that I am unlikely to overload the supply in reality, but not sure if I can justify such a large load sufficiently by any recommended method and so sign off the work in surety.
I have considered using a shower priority or NO/NC contactor for sauna and shower but wished to get the forum thoughts on the loading for this situation.

Thank you

 

[trev]

The osg says other methods of calculating a diversified load are allowed so as long as you can justify the method then you'll be fine mate

 

[Richard Burns]

OK measured load on house is 20A, maximum likely load on house in worst case is 40A for about 30 min, 20A over one hour.
Maximum likely load from room is 60A for 15mins, 30A over one hour.

Fuse will cope in this case but 100A for 15 min might be considered pushing it, but in reality would they really be cooking on hob and oven, washing their clothes with sauna on and using the shower, whilst heating the adjacent room?

Would this be considered a justified approach?

 

[Marvo]

I'm not sure what your best practices say in the UK but when it comes to diversity there's no substitute for common sense after doing some homework on the customers usage patterns. We would always approach it on a case by case basis because there's so many relevant factors that most tables don't take into account the resulting predictions can be hit and miss.

If necessary we would also warn the customer in writing that the supply should ideally be upgraded in capacity but if they choose not to there might be a possibility of occasional tripping problems. Also any tripping that occurs shouldn't be seen as a fault per se, rather as the protection device doing the job it's supposed to be doing.

 

[Deleted member 26818]

Have you measured the load at the tails with everything switched on?

 

[Richard Burns]

Have you measured the load at the tails with everything switched on?

No only with normal usage when the cooker was heating and washing machine heating 20.5A, once washing machine off heating but spinning 10.5A once cooker not heating 1.5A
Total appliance load in kitchen is 40A ring +18A cooker at peak (but will never be reached) and only 15A outside kitchen as there are no electric heaters and only an immersion (which would probably be unused).

 

[Engineer54]

Well it'll be highly unlikely that the Sauna and the 7.5 KW shower will be used simultaneously, and even if they were, it would be for very short periods of time. You're original guesstimate of a maximum draw on this supply of 60A (taking everything you have stated so far) is a far more realistic figure than even you might think it is...lol!!!

 

[i=p/u]

stick a screw in til you get payed,,,,,, but i know thats not your style.. so jokeeeeeeeeeeeeeeeeee:mickey:

 

[sparks1973]

OK measured load on house is 20A, maximum likely load on house in worst case is 40A for about 30 min, 20A over one hour.
Maximum likely load from room is 60A for 15mins, 30A over one hour.

Fuse will cope in this case but 100A for 15 min might be considered pushing it, but in reality would they really be cooking on hob and oven, washing their clothes with sauna on and using the shower, whilst heating the adjacent room?

Would this be considered a justified approach?

go for a consultation with the person ordering the work Richard.....find out what their patterns are...say teatime (worst case)....and sundays (Dinner)......could you not base your loadings on that?...