Calculation Of Max Demand Within An Electrical Installation

[electau]

Here is a method (by calculation) to calculate max demand. This method is based on AS3000.

This information should be used as a guide only. This method is the most economical as far as costs and with general usage ( diversity) within an installation.

A. Lighting. 3A for up to 20 points. 2 A for the next 20.

B. Socket outlets (10A). 10 A for the first 20 and 5A for the next 20.

C. Hotplates. Clothes dryers over 10A 50% of connected load.

D. Airconditioning. 75% of connected load for units over 10A.

E. HWS storage type. Full connected load. Instantaneous type 33.3% of full connected load.

Thus for a residence with the following.

20 lighting points = 3A

20 socket outlets = 10A

Hotplate unit 7000W = 3500W = 16A.

Airconditioning 5000W input.= 3750W =17A

Instantaneous HWS. 6000W = 2000W= 9A.

Total max demand 55A.

This is for a single phase installation. for a three phase installation the load is balanced over the 3 phases. Most residential installations do not require a 3 phase supply.

The above is the calculation method. The other is by limitation of max demand by the use of an MCB.

The MCB used as a main switch effectively limits the max demand to the continuous rating of the device.

Number of circuits to an installation. Minimum.

Lighting 2.

Socket outlets 2.

Hotplates,Clothes dryers 1 individual circuit for each.

Airconditioners 1 individual circuit for each.

HWS 1 individual circuit for each.

Main switch. 1 x 2 pole MCB.

Calculate the max demand first, before purchasing any electrical equipment over 10A. Then approach the PEA to see if they can service that load in accordance with their conditions of supply.

[linno2]

Excellent timing - just looking for a chung fi for the house as we are in the middle of lifting up 1.1meters so we are well above the road that has been elevated by our local council to now be higher than the floor of our house - hence 3 floods through the front door in the last 4 years. I can now sit down and work out the specification for the supply and tradesman. MANY THANKS ELECTAU

[Crossy]

Thanks for that electau, a calculation that actually gives sensible MD results for a location where portable heaters are not in abundance (which is the issue with using UK based calculators).

[electau]

Here is a method for calculating number of point on a final subcircuit. Use as a guide only. Based on AS3000.

Lighting and Fan points. 0.25amps each point ( 60W) max number of points per circuit unlimited. Not to exceed the current rating of the cable.

Power 10A socket outlets. Max number per circuit 20. 1A per point, a twin outlet is 2 points.

Minimum cable sizes Lighting and Fans 1.0sqmm 10A, or 1.5sqmm 16A. Power 10A socket outlets 2.5sqmm 20A.

HWS, Airconditioners and permanently connected equipment with a full load rating over 10A. Full load current.

[jombom]

Excellent timing - just looking for a chung fi for the house as we are in the middle of lifting up 1.1meters so we are well above the road that has been elevated by our local council to now be higher than the floor of our house - hence 3 floods through the front door in the last 4 years. I can now sit down and work out the specification for the supply and tradesman. MANY THANKS ELECTAU

Not too clever on your part ---- so what can you do ???

At a guess it looks like the local council has raised the road to avoid flood conditions.

[David006]

interesting....where do economics enter? Are you referring to the hardware involved or paying PEA for service over and above what is available at the pole?

Trouble is at the end of the day it is just about the size of the service available from PEA especially in rural areas. "No have" .."cannot"..lol

Still trying to calculate why we have long outages on calm cloudless days?

[David006]

Think the simplest way to guesstimate service current demand for the DIYer is just to add up the wattages of guesstimated number and type of appliances , lights etc which are likely, on average, to be in use at any one time and divide by 240?

Not a function of how many outlets really.

Unless you have a mansion and/or excessively high wattage stuff, probably an exercise which is just, for the average DIYer's domicile, a "nice to know".

As you say, limited by the main breaker or the whole house GFI rating anyway

BTW, a good idea, in places like the kitchen, is to have each outlet of duplexes wired to separate breakers....it is probably already someplace in your ASXXXX bible...it is in the Canadian "Redbook".........555

[electau]

The method that one has mentioned is based on AS3000 and is intended as a guide only.

One when calculating max demand tries to obtain the lowest figure in amps per phase.

Economic cost is very important to consumers with regard to electrical installations.

Different standards may have other methods eg BS, IEC, NEC ( US).

Adding up the amps/watts of each item of electrical equipment to obtain max demand is not a very good method for residential/domestic electrical installations. Yes, there is a clause in AS3000 that maximum demand MAY be calculated by adding up all the ratings of the MCBs on final subcircuits, it does not apply to domestic installations.

Yes, socket outlets should be distributed over 2 circuits ( or more) in a kitchen area, this is required under AS3000.

Thailand does have electricity supply problems on its network, some outages may be due to load shedding and some to equipment failure, some may be attributed to system operator error.

[jcw]

Thanks for making the effort.

I nominated you here by the way last week. I find this stuff really helpful to have int he archives to find when you need it.

[electau]

Thanks for making the effort.

I nominated you here by the way last week. I find this stuff really helpful to have int he archives to find when you need it.

The problem with standards in Thailand is that there are very few, and in many cases cannot be legally enforced by legislation. The Thai government takes zero interest into safety for electricity consumers, which could be done through the PEA and MEA.

Unlike Malaysia and Singapore.

Edited December 6, 2012 by electau

[David006]

The method that one has mentioned is based on AS3000 and is intended as a guide only.

One when calculating max demand tries to obtain the lowest figure in amps per phase.

Economic cost is very important to consumers with regard to electrical installations.

Different standards may have other methods eg BS, IEC, NEC ( US).

Adding up the amps/watts of each item of electrical equipment to obtain max demand is not a very good method for residential/domestic electrical installations. Yes, there is a clause in AS3000 that maximum demand MAY be calculated by adding up all the ratings of the MCBs on final subcircuits, it does not apply to domestic installations.

Yes, socket outlets should be distributed over 2 circuits ( or more) in a kitchen area, this is required under AS3000.

Thailand does have electricity supply problems on its network, some outages may be due to load shedding and some to equipment failure, some may be attributed to system operator error.

Suspect the PEA actually calculates/ed a mean max demand in designing their network..probably done way before the prevalence of aircon,pumps etc.

cheers

d

[electau]

The method that one has mentioned is based on AS3000 and is intended as a guide only.

One when calculating max demand tries to obtain the lowest figure in amps per phase.

Economic cost is very important to consumers with regard to electrical installations.

Different standards may have other methods eg BS, IEC, NEC ( US).

Adding up the amps/watts of each item of electrical equipment to obtain max demand is not a very good method for residential/domestic electrical installations. Yes, there is a clause in AS3000 that maximum demand MAY be calculated by adding up all the ratings of the MCBs on final subcircuits, it does not apply to domestic installations.

Yes, socket outlets should be distributed over 2 circuits ( or more) in a kitchen area, this is required under AS3000.

Thailand does have electricity supply problems on its network, some outages may be due to load shedding and some to equipment failure, some may be attributed to system operator error.

Suspect the PEA actually calculates/ed a mean max demand in designing their network..probably done way before the prevalence of aircon,pumps etc.

cheers

d

Allowing for diversity on the distribution system the calculation is most likely around 10A per phase per individual installation.