Electric 'Loadings'

[bobby62]

Just after some advice please guys

I need to fill in a form for United Utilities regarding an upgraded electric supply. There is a section that asks for the anticipated loadings. Is there a rough way of working out what the load requirements may be i.e. no. of lights, small loads etc. do they normally require the anticipated amount of kW's required?

 

[Steve]

Whats the old supply? What are you upgrading it to?

 

[Chri5]

Could you expand further?

What have you got at the moment ? Why isn't that enough / and what do you want?

Older house have 60A
Newer should be 100A
and everything over 100A will be a 3 phase supply which means 3P fuse boards.

Your average 3/4 bed house should be fine with 100A, if your lucky enough to own a 8 bed house with play room, gym and indoor swimming pool then 3P is the norm.

100A x 230v = 23kw or 23000w.

Do you understand diversity? Which works on the principle that you could have say

4 x 32A circuits
4 x 6A circuits
1 x 40 A circuit
1 x 45 A circuit
2 x 20A misc circuits

Total would be 257A but diversity works on the fact that not every circuit is working 100% all the time.

I have an old 60A supply, but with circuits in the region of the example above and have never suffered a main head fuse blow due to excessive load demand.

Maximum demand is calculated as follows.

Lighting - 66% of the total current demand i.e add up all the lamps on your circuit and take 66% of that number.

Power - 100% of first ring circuit i.e 32A + 40% of all of all other ring circuits

Cooker - first 10A + 30% of the full load of the appliance over 10A + 5A if there is a socket outlet on the control unit.

If you have an instantaneous (electric) boiler then assume 100% demand,
also if its thermostatically controlled then there is no diversity allowable so you assume the current rating of the appliance

Shower - no diversity allowable

 

[bobby62]

Thanks, the job is not a domestic house, it is an upgrade to a supply currently serving a large site with 2 existing buildings and 2 new buildings. It only has to be a rough guide as lighting and socket circuits have yet to be decided. How many kW can a domestic supply serve is is around 20kW?

I would say the new buildings would compare to 2 large houses.

 

[Chri5]

Thanks for no mentioning that earlier, thanks for wasting my time (given freely to TRY and help).

Diversity doesn't apply to commercial buildings.

Read this PDF http://www.nfpa.org/assets/files//PDF/necdigest/CodeIssues072704.pdf

Alternatively use the services of a commercial electrical designer, getting your figures wrong will end up costing you in delays, money and failure to match the build requirements with the load.

Next your be telling us it's a commercial data centre with 5000 x data rack each eating 4 kw per hour 24/7 x 365

 

[Adam_151]

Diversity doesn't apply to commercial buildings.

Of course it does!

(its just that you can't apply the same factors as domestic!)

 

[ban-all-sheds]

Thanks, the job is not a domestic house, it is an upgrade to a supply currently serving a large site with 2 existing buildings and 2 new buildings. It only has to be a rough guide as lighting and socket circuits have yet to be decided. How many kW can a domestic supply serve is is around 20kW?

I would say the new buildings would compare to 2 large houses.

Bobby - OOI, in what capacity, exactly, are you filling in this form for UU?

 

[Stoday]

Two existing and two new commercial/indusrial buildings. Estimating the site maximum demand is a specialist job.

Estimate too high and connection charges escalate exponentially. Estimate too low and you pay a second time for an upgrade. Getting it wrong has become even more expensive since 2005 when connection charges were changed so you now pay the full cost of the connection plus the cost of any network reinforcement that is necessary.

It's more difficult with new buildings because you have to sort out the supply before you know fully what's going in them.

Pays to employ a consultant such as: Click Here
.