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C5.1 Calculation of maximum demand in single and multiple domestic electrical installations (Paragraph C4 and Table C1)

C5.1 Calculation of maximum demand in single and multiple domestic electrical installations (Paragraph C4 and Table C1)

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252

AS/NZS 3000:2000

Solution
The method of determining demand in accordance with Table C1 is as
follows:
Load Group A(i) —
24 lighting points, plus
10 m of lighting track, plus
50 W exhaust fan = 45 points
=3+2+2=7A
Load Group A(ii) —
3000 W tennis court lighting = 12.5 × 0.75 = 9.4 A
Load Group B(i) —
9 × 10 A single socket-outlets, plus

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8 × 10 A double socket-outlets = 25 points
1000 W strip heater = 1 point
= 10 + 5 = 15 A
Load Group B(ii) —
15 A socket-outlet = 10 A
Load Group C —
10 000 W range = 41.67 × 0.5 = 20.8 A
Load Group F —
Water heater 4800 W = 20 A
Total
demand

=

Sum of load group demands = A(i) + A(ii) + B(i)
+ B(ii) + C + F

=

7 + 9.4 + 15 + 10 + 20.8 + 20

=

82.2 A

Example 2
Determine the maximum demand of the heaviest loaded phase in a
domestic electrical installation comprising —
26
lighting points
24
10 A single socket-outlets
1
15 A socket-outlet
1
16.6 kW range
1
4 kW air-conditioning unit
1
12.96 kW instantaneous water heater
1
3.6 kW clothes dryer

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253

AS/NZS 3000:2000

and arranged for connection across a three-phase supply as follows:
Red

White

Blue
26 lights
15 × 10 A socket-outlets 9 × 10 A socket-outlets

15 A socket-outlet
5 kW hotplates

6.6 kW oven

5 kW hotplates

4 kW air-conditioner
4.32 kW instantaneous 4.32 kW instantaneous 4.32 kW instantaneous
water heater
water heater
water heater
3.6 kW clothes dryer
Solution
The method of determining the demand in the heaviest loaded phase in
accordance with Table C1 is as follows:

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Equipment

Load Group Column

Red
A

Lighting

A(i)

2

10 A socket-outlets

B(i)

2

15 A socket-outlet

B(ii)

2

10

Range

C

2

10.4

Air-conditioner

D

2

12.5

Water heater

E

2

6

Clothes dryer

C

2

White
A

Blue
A
5

10

10

10.4

13.7

6

6

7.5
38.9

33.9

34.7

Total loading, heaviest loaded phase = Red phase, 38.9 A.
Example 3
Determine the maximum demand of the heaviest loaded phase of a block of
80 units comprising the following loads:
Lighting:

80 units.

10 A socket-outlets:

80 units.

Electric ranges:

17 units.

2.5 kW (10.4 A) permanently connected strip heaters:

80 units

Quick recovery water heaters:

80 units

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254

AS/NZS 3000:2000

Loading not associated with the individual units (communal services):
Communal area lighting and power
90

60 W lighting points

21

100 W lighting points
(Total lighting 7.5 kW)

20

10 A single socket-outlets

10

3.6 kW clothes dryers

2

12 kW lift motors

1

5.5 kW 3-phase pump motor

1

4 kW 3-phase water supply motor

Solution

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The method of determining the demand of the heaviest loaded phase,
assuming that the electrical installation is balanced as far as practicable
over the three phases, in accordance with Table C1 is as follows:
Number of units per phase, three-phase supply = 80/3 = 27 units over each
of two phases and 26 units on the other phase. The instructions given in
Column 5 of Table C1 would therefore be applicable to the electrical
installation other than for the electric ranges.
The number of electric ranges per phase = 17/3 = 6 over each of two
phases and 5 on the other phase. The instructions in Column 4 of Table C1
would therefore be applicable to the Load Group C, ranges and cooking
appliances.
Individual units (27 units)
Equipment

Load Group Column

Calculation

Result

Lighting

A(i)

5

27 × 0.5

=

Socket-outlets

B(i)

5

50 + (27 × 1.9)

= 101.3 A

Electric ranges (6 units)

C

4

6 × 2.8

=

Strip heaters

D

5

27 × 10.4 × 0.75 = 210.6 A

Water heaters

F

5

100 + (27 × 0.8)

Total units loading for heaviest loaded phase

13.5 A
16.8 A

= 121.6 A
= 463.8 A

Communal services The lighting is taken as being evenly balanced over
the phases, i.e. 7500/3 = 2500 W per phase. (Should the lighting load be
arranged for connection to one phase, the loading for Load Group H would
be 7500 W.)
The 20 socket-outlets are taken as connected, 7 over each of two phases
and 6 on the other phase.

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AS/NZS 3000:2000

The 10 clothes dryers are taken as connected, 3 over each of two phases
and 4 on the other phase: loading on heaviest loaded phase = 14 400 W.
Motors:

5.5 kW motor

=

10.4 A per phase (nameplate rating)

4 kW motor

=

8.3 A per phase (nameplate rating)

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Equipment

Load Group

Column

Calculation

Result

Lighting

H

5

2500
240

=

10.4 A

Socket-outlets

I

5

7×1 =

7.0 A

Clothes dryers

J(i)

5

 14 400 
0.5 

 240 

Lifts

K

5

Nil

Motors

L

5

=

30.0 A


10.4 + (8.3 × 0.5) =

14.6 A

Total communal services loading for heaviest loaded phase =

62.0 A

Total loading for heaviest loaded phase:
= units loading + communal services loading
= 463.8 + 62.0 = 525.8 A
C5.2 Calculation of maximum demand in non-domestic electrical
installations (Paragraph 4 and Table C2)
Example 4
Determine the maximum demand of the heaviest loaded phase of a 30 unit
motel complex supplied by three-phase with the following load:
200

60 W lighting points

30

50 W 1-phase exhaust fans (permanently connected)

10

10 A 1-phase single socket-outlets (non-permanently heated or cooled
area)

90

10 A 1-phase single socket-outlets (permanently heated or cooled
area)

4

15 A 1-phase socket-outlets

1

16.6 kW 3-phase electric range

1

0.75 kW 3-phase sewerage pump motor

1

6 kW 1-phase sauna heater

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256

AS/NZS 3000:2000

The load is arranged for connection across the three phase supply as
follows:
Red
White
Blue
70 lights
70 lights
60 lights
10 exhaust fans
10 exhaust fans
10 exhaust fans
5 × 10 A
5 × 10 A
socket-outlets B(i)
socket-outlets B(i)
30 ×10 A
30 × 10 A
30 × 10 A
socket-outlets B(ii)
socket-outlets B(ii)
socket-outlets B(ii)
1
× 15 A socket-outlet
1 × 15 A socket-outlet
2 × 15 A socket-outlets
5 kW hotplates
6.6 kW oven
5 kW hotplates
0.75 kW pump
0.75 kW pump
0.75 kW pump
6 kW sauna
Solution
The method of determining the demand in the heaviest loaded phase in
accordance with Table C2, Column 2 is as follows:
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Equipment
70 light points

Load
Group
A

Calculation
70 x 60 W
× 0.75
240

60 light points

A

10 exhaust
fans

A
10 x 50 W
× 0.75
Foot240
note c

5 × 10 A
socket-outlets

B(i)

30 × 10 A
socket-outlets

B(ii)

1 × 15 A
socket-outlet
2 × 15 A
socket-outlets
6.6 kW oven
5 kW hotplate
0.75 kW
sewer pump
6 kW sauna
heater

B(iii)

2600 W
240
3900 W
1000 + (29 × 100 W ) =
240
Full current rating

B(iii)

15 A + (15 A × 0.5)

C
C
D

Full connected load
Full connected load
Full load (nameplate rating)

G

Full load current

Red White Blue
A
A
A
13.13 13.13
11.25

60 x 60 W
× 0.75
240

1000 + ( 4 × 400 W ) =

1.56

1.56

1.56

10.83 10.83
16.25 16.25 16.25
15.0

15.0
22.5

27.50
2.0

20.83 20.83
2.0
2.0
25.0

86.27 87.10 91.89
Total loading, heaviest loaded phase = Blue phase, 91.89 A
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