Diversity and Maximum Demand

[Steve_M]

I'm having two new supplies installed into two adjoining small cottages (currently they are fed, inadequately off a three phase supply).

Scottish Hydro are installing two single phase supplies with a maximum capacity of 100 amps each property.

Heating will be electric using a "Total Heat Total Control" tarriff. This is a three way split tarriff.

My concern is regarding the maximum demand.

10 x 100w on the lighting circuits = 1000w at 66% = 2.87a
Kitchen ring assuming full load = 32a
Ground & First Floor rings = 6a
Shower 8.5Kw = 37a
Cooker, 40a (10a+30% 0f 30a) = 19a
Panel Heaters total 24a (10a+50% 0f 14a) = 17a
Thats almost 114a, then add;
Immersion 3Kw = 13a
Storage Heaters, 6Kw = 26a
Total potential load 153a

Am I right to be concerned? surely there is nothing here that is different to thousands of other consumers using electric heating but I'm concerned that the load will just blow the service fuse.

Also the quote from the Hydro says "with a maximum capacity of 100 Amperes subject to an after diversity maximum demand of 10kVA for each property" What does this mean?

 

[plugwash]

so you currently have a 3 phase supply and you are getting 2 seperate single phase supplies?

how big is the 3 phase supply? it would have to be a very small 3 phase supply for 2 100A single phase supplies to be an improvement

i think it will probablly be ok but it is close to the line

one possibility if the rec are prepared to do it would be to bring 3 phase in and use 1 phase for each houses main supply and the third phase for the off peaks

a final possibility would be some form of breaker discrimination system but i think those are very expensive

 

[Lectrician]

You are signing up to a 10kva deal on a 100amp fuse - you are saying your maximum demand will generally be 10kva (40 ish amps).

A common misconception - the fuse rating isnt the maximum demand. larger properties have to pay availability charges on their stated maximum demand aswell.

 

[Steve_M]

Plugwash: The three phase is left over from when the property was a working farm. At some point in the past the cottages have been wired through one of the phases. The route taken is a good 100m and it has been done in 4mm single core cables - thats the bit I mean by inadequate supply. We are planning the new supplies so we can have off peak tariffs and we will have the three phase taken out at some point.

Lectrician: Presumably this means that they are expecting to provide us with 40a (ish)? Surely this would not be sufficeint in most cases even without electric heating.
How would this work/what would happen if (when) we were drawing more?

 

[Lectrician]

The electricity boards max demand figures are very different from that of our regs.

Diversity can be applied across circuits, you have applied diversity to each circuit, but not considered that the cooker may be off when the shower is on, one panel heaters thermostat may be off when another is on etc.

If you take more than the ageed capacity on a domestic supply, no action is usually taken. Many people exceed the maximum demand, upto the fuse rating.

If you pop a fuse more than a couple times, this is when they look into hte situation.