Electrical. Max Demand Requirements

[david96]

When calculating Max demand (MD) requirements in Thailand for a single residential electrical installation the choices one has are:

Single phase 100A. MD. minimum size consumers mains 25sqmm or,

Single phase 45A. MD. minimum size consumers mains 10sqmm.

Connection across 3 phases may be permitted with consultation with the PEA, but the total MD requirements remain the same.

Metering is the responsibility of the PEA and is installed on the line (supply) side of the main switch. A service protective device (HRC fuse) may not be installed.

The PEA should advise where the consumers mains commence, this would be at the point

where the service conductors connect with the consumers mains, this may be at the load terminals of the meter. The service conductors terminate at the distribution conductors which originate at the distribution transformer.

The actual size of the consumers mains would be subject to voltage drop requirements.

Voltage drop calculations under AS3000/2007 commence at the start of the consumers

mains not the service conductors. It is 5% max to any point in the installation. For calculation purposes the nominal voltage should be regarded as 220V at the point where the consumers mains commence for a single phase installation.

If one keeps their MD equal to or less than 100A or 45A one will have no problems.

Once the MD has been calculated one then calculates the voltage drop on the consumers mains. To do this one will require the proposed route length in meters of the cable run. Generally (but not always) up to 50% of the permitted voltage drop is in the consumers mains and the remainder in the final sub circuits.

Therefore the MD must be caculated first, before one installs any cabling or purchases any electrical equipment.

Always try to minimise your MD not maximise it. Consider solar for HW or use storage types instead ( 7.5A or 15A single phase). Try to avoid using instantaneous water heaters over 15A single phase and consider using LPG for cooking purposes.

It is loads over 10A that will affect your MD.

Airconditioning load may be a large part of the MD so it needs to be assessed accurately.

A competent air conditioning contractor should be able to calculate the number of A/C units for your requirements from the following, floor area, floor type, wall type, ceiling type, insulation, height of ceiling (2.6 - 3.0M) window area, average number of occupants, etc.

And always look at diversity within an electrical installation. And remember, the further your house is from the power infrastructure the larger the consumers mains are going to be due to voltage drop considerations.

[david96]

Max demand in mains and sub mains by calculation. ( Ref. AS3000/2007 ). This can be used in Thailand for calculating the MD in a single residential installation.

A.(1). Lighting and fan points. 3A for the first 1-20 points plus 2 A for each 20 additional points or part thereof. (2). Outdoor lighting exceeding 1000W, 75% of connected load.

B.(1) Socket outlets not exceeding 10A. Permanently connected electrical equipment not exceeding 10A and not included in other load groups.

10A for the first 1- 20 points plus 5A for each additional 20 points or part thereof.

B.(2). 1 or more 15A socket outlets not in groups C,D,E and F. 10A.

B.(3). 1 or more 20A socket outlets not in groups C,D,E,and F. 15A

C. Ranges, Electric cooking appliances,laundry equipment or socket outlets rated at more than 10A for the connection thereof. 50% of connected load.

D. Fixed Airconditioning or space heating equipment permanently connected or connected to socket outlets rated at more than 10A for the connection thereof. 75% of connected load.

E. Storage HWS. Full connected load.

F. Instantaneous water heaters. 33.3% of connected load. Includes " quick recovery" heaters having an element rating greater than 100W/L.

Notes.B.(1). For the purpose of determining MD a multiple combination socket outlet shall be regarded as the same number of points as the number of integral socket outlets in the combination.

A water pressure pump not exceeding 10A may be regarded as an extra point under load group B.(1).

Here is an example of a MD calculation.

Load group A1. 30 points.

Load group B1. 46 points (23 twin 10A socket outlets)

Load group C. 1 x 20A 4 x hotplate unit.

Load group D. Airconditioners 6 x 8.8A each.

Load group E. 1 x 15A HWS.

Load group A1. 3A + 2A = 5A

Load group B1. 10A + 5A +5A = 20A

Load group C. 20A x 50% = 10A

Load group D. 6 x 8.8A = 52.8A.x 75% = 36.9A

Load group E. 15A.

Total A1+B1+C+D+E = 5A+20A+10A+36.9A+15A = 86.9A. MD.

[elkangorito]

DGPO=double general purpose outlet (a power outlet that can accommodate 2 plugs).

SGPO=single general purpose outlet (a power outlet that can accommodate 1 plug).

In addition to what David has said, I recommend the following:

1] a minimum of 1 x DGPO & a maximum of 2 x DGPO's per bedroom.

2] the kitchen is a "special" area & it should have it's own circuit regarding GPO's (dedicated circuit). Usually 2 to 4 x DGPO's.

3] laundry - 1 x DGPO.

4] living room - 4 x DGPO's (minimum).

5] dining room - 2 x DGPO's (maximum).

6] bathroom - 1 x DGPO's protected by a 10mA RCD (dedicated circuit).

7] garage/carport - 1 x DGPO.

8] workshop (garage?) - maximum demand shall be determined upon requirements. At least 2 x DGPO's.

9] Hallways - unless you live in a huge mansion, GPO's in hallways are not required.

10] Lights - as required, unless the lights are of higher power than usual (floodlights etc).

I have missed some areas but they are minor unless the load of the equipment is unusually high. Usually, "plug in" equipment is not specifically addressed in a maximum demand calculation unless it is peculiar in some way.

Unless you wish to use every single electrical device ever invented - all day & everyday, these limits should be ample for your abode. There is no reason why a "normal" home should require more than an 80 amp single phase service.

Unfortunately, Thai "electricians" do not seem to have any idea about maximum demand & nor do they seem to understand load balance across three phases. Also, the energy providers (PEA etc) do not seem to provide any advice in this regard.

Good luck & Merry Christmas.

Edited December 18, 2009 by elkangorito