diversity, load and all that!!

[MrF]

Another question about my garage and basement. (the load is getting bigger) I have been reading up about diversity in the brown on site guide and am getting confused and the subject is getting more interesting.
Basicaly to recap, I am having a new garage with basement built and i am trying to work out how to supply it.

The load for my two lighting circuits is 8.8A (66% of total)
I have two rings so i have taken one at 32A and 40% of other at 12.8A
Am i right so far???
Now i am going to throw in TWO 12Kw water heaters (no diversity)
giving me a total of 153.6A
If this is right will i need a new supply? as the house supply would not be able to cope and if consumer units are rated at 100A would i need two?
(Note to lectrician i do have a 100mA RCD. thanks for previous info.)
Thanks MrF

 

[andy]

12KW heater?

you must use some hot water

 

[Adam_151]

Three phase with water heaters each on their own phases, and the rings and lights on the remaining one?

 

[MrF]

the 12Kw heaters will be running underfloor heating one for each floor

 

[andy]

the 12Kw heaters will be running underfloor heating one for each floor

oh. youll need a 3 phase supply. 12KW is quite a bit juice. do as mentioned, and have the heaters on 1 phase etc. as for the 100A RCD, it is 100A per phase, not 100A in total

 

[revolt3k]

hi dude

hey why not just install a combi boiler and run that for your underfloor heating>?

would work out cheaper in the long run

Reason's

1. New 3 phase min £2000 to get installed to the house

2. Cost of sparky to install

3. Combi £400-500 for unit on its own + underfloor stuff - £1500 ish so you will save a ton, plus would cost less to run the stuff 2x 12KW will be thirsty if always run.

 

[MrF]

Don't have gas but am considering another oil boiler for garage.

 

[felix]

24kW is a tremendous amount of heat. The average house runs nicely on a 50,000 btu/hr (15kW) boiler which also does the hot water - and, unless the temperature is well below zero outside, it's not on all the time.

You should do a heat loss analysis for your new garage/basement and work out how many kilowatts you really need. If those two 12kW water heaters really are on all the time then either:

1) You live on Baffin Island or -
2) Most of the heat is going straight into the ground or -
3) You're an alien from Venus and you don't like our climate!

What I'm trying to say here is that those two water heaters are NOT going to be on all the time. Unfortunately, there is a possibility that both will be on at the same time and that's a problem because 24kW is the limit of your existing 100A supply.

If the heaters are already installed then I don't see an easy way out. You'll could rig up a time switch such that each heater gets its own time slot. The two heaters could then go on a single 50 amp breaker - though only just! Switching 12kW is beyond the capability of any readily available timer so you'll need some heavy duty contactors as well.

 

[Stoday]

I've seen a heating installation like that. It might have been 30kW, wet underfloor electrically heated.

The installation was most impressive and the owner very proud of it. His name was Rothschild.

MrF's place wouldn't be near Wing would it?