Maximum Demand Estimation in a Single Domestic Electrical
Installation (simplified version).
What is Maximum Demand?
It is the highest current used by an installation based upon an estimated ‘usage’ of each & every
electrical fitting/appliance.
How can estimating the Maximum Demand of my installation help me?
It can help to size your Consumer Mains (the cables from the street power pole to your Kilowatt
Hour Meter) appropriately. In Thailand, knowing your Maximum Demand will also help you to
select the appropriate size Kilowatt Hour Meter.
Maximum Demand does not allow for future expansion, however, any future expansion can
be ‘built in’ to an initial Maximum Demand calculation.
To estimate Maximum Demand;
1. Lighting (internal).
3 amps for 1-20 points & an extra 2 amps for each additional 20 points.
A 'point' is;
a)
An incandescent light not exceeding 60 watts. If fittings hold multiple globes, each
individual globe shall count as 1 point if the light fitting does not permit each globe to be
above 60 watts.
b)
0.5 metre of track lighting.
2. Lighting (external).
If total outdoor lighting exceeds 1000 watts 75% of total load.
If the total outdoor lighting is less than 1000 watts, calculate as for 'internal lighting'.
Example, if you have a total outdoor lighting wattage of 2500 watts, the n the demand would be;
2200 divided by 220, which equals 10 amps. 75% of 10 amps equals 7.5 amps.
3. Instantaneous Water Heaters.
33% of connected load.
For example, for a 3300 watt instantaneous water;
3300 divided by 220 equals 15 amps. 33% of 15 amps equals 4.95 amps (5 amps).
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Maximum Demand estimation in a Single Domestic Residence
Maximum Demand Estimation in a Single Domestic Electrical
Installation (simplified version) cont.
4. Socket Outlets (power points).
10 amp socket outlets.
10 amps for 1 to 20 points & 5 amps for each additional 20 points or part thereof.
Even though a socket outlet (power point) may have multiple points per fitting, each fitting as such
is counted as 1 fitting.
This does not include socket outlets mounted at greater than 2.3 metres above the floor &
where such sockets will not have equipment exceeding 150 watts connected. Such outlets can
be classed as an ‘internal lighting point’.
15 amp socket outlets (not for any specific equipment).
10 amps for each 15 amp socket outlet.
5. Ranges, cooking appliances, laundry equipment or socket-outlets rated at more than 10
amps & for the connection thereof.
50% of connected load.
6. Fixed space heating or air-conditioning equipment, saunas or socket-outlets rated at more
than 10 amps & for the connection thereof.
75% of connected load.
7. Storage water heaters.
Full load current.
8. Spa and swimming pool heaters
75% of the largest spa, plus 75% of the largest swimming pool, plus 25% of the remainder.
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Maximum Demand estimation in a Single Domestic Residence