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SECTION 6: CIRCUIT LOADING AND DEMAND FACTOR
SECTION
6
CIRCUIT LOADING AND DEMAND FACTOR
6.1 SCOPE
(1) This section covers conductor ampacities and equipment ratings required for consumer's services,
feeders and branch circuits.
6.2 NORMATIVEREFERENCES
(1) The following references contain provisions which, through reference in this text, constitute
provisions of the Ethiopian Building Code Standard on Electrical Installation of Buildings.
(a) CSA C22.1:2002
Canadian Electrical Code, Safety Standard for Electrical
Installations Nineteenth Edition.
(b) NFPA 70 / NEC:2005
National Electrical Code Handbook Based on the 2005 (NEC),
Tenth Edition, IEC series
(c) BS 7671:2001
Requirements for Electrical Installations, IEE Wiring
Regulations, Sixteenth Edition.
6.3 DEFINITIONS
(1) For the purpose of this Section, the following definitions shall apply in addition to the terms defined in
Section 1.
Demand factor
it is the ratio of the maximum demand of a system or part of a
system, to the total connected load on the system, to the
maximum demand of the whole system, or part of a system,
under consideration.
ETHIOPIAN BUILDING CODE STANDARD
EBCS-10: 2013
SECTION 6: CIRCUIT LOADING AND DEMAND FACTOR
Diversity factor
the ratio of the sum of the individual maximum demands of the
various subdivisions of a system, or part of a system, to the
maximum demand of the whole system, or part of a system,
under consideration.
Continuous load
any condition in which the maximum load current in a circuit
flows without interruption for a period of not less than 3.0hrs.
6.4 GENERAL
6.4.1 Current Calculation
(1) When calculating the currents from loads expressed in watts or volt-amperes, to be supplied by a low
voltage a.c. system, the voltage divisor to be used shall be 230.0V or 380.0V as applicable.
6.4.2 Voltage Drop
(1) Voltage drop in an installation shall be based upon the calculated demand load of the branch circuits
and shall satisfy the requirements of Clause 4.5.4.
6.4.3 Maximum Circuit Loading
For loads other than motors, the total load on consumer's service, feeder or a branch circuit shall be 80%
of the circuit rating when the load is a continuous one.
6.4.4 Use of Demand Factor
(1) Where two or more loads are so installed that only one can be used at any one time, the one providing
the greatest demand shall be used in determining the calculated demand.
(2) Where a feeder supplies loads of a cyclic or similar nature such that the maximum connected load will
not be supplied at the same time, the ampacity of the feeder conductors shall be based on the maximum
load that may be connected at any one time.
(3) The ampacity of conductors of a feeder or branch circuit shall not exceed the ampacity of the
conductors of 'the service or of the feeder from which they are supplied.
6.5 SERVICES AND FEEDERS
6.5.1 Single-Family Dwellings
(1) The minimum ampacity of service or feeder conductors supplying a single-family dwelling shall be
based on the following:
ETHIOPIAN BUILDING CODE STANDARD
EBCS-10: 2013
SECTION 6: CIRCUIT LOADING AND DEMAND FACTOR
(a) a basic load of 2500.0W for the first 70.0m2 of living area; plus
(b) an additional 1000.0W for each 70.0m2 or portion thereof in excess of 70.0m2; plus
(c) 3500.0W for any electric "Injera Mitad"; plus
(d) 6000.0W for a single cooking stove having a rating of 12.0kW or less, plus 40% of the amount by
which the rating of the cooking stove exceeds 12.0kW; plus
(e) any electric water heater with a demand factor of 100%.
6.5.2 Apartment and Similar Multi-Family Buildings
(1) The minimum ampacity of service or feeder conductors from a main service supplying loads in
dwelling units shall be based on the following:
(a) a basic load of 2500.0W for the first 45.0m2 of living area; plus
(b) an additional 1500.0W for the second 45.0m2 or portion thereof; plus
(c) an additional 1000.0W for each 'additional 90.0m2 or portion thereof in excess of the initial
90.0m2; plus
(d) 3500.0W for any electric "Injera Mitad"; plus
(e) 6000.0W for a single cooking stove having a rating of 12.0kW or less, plus 40% of the amount by
which the rating of the cooking store exceeds 12.0kW; plus
(f) any electric water heaters with a demand of 100%
(2) The minimum ampacity of service or feeder conductors from a main service supplying two or more
dwelling units shall be based on the calculated load obtained from Clause 6.5.2(1) and the following:
(a) Excluding any air-conditioning loads, the load shall be considered to be:
i) 100% of the calculated load in the unit having the heaviest load; plus
ii) 65% of the sum of the calculated loads in the next 2 units having the same or next smaller load to
those specified in (i) above; plus
iii) 40% of the sum of the calculated loads in the next 2 units having the same or next smaller loads to
those specified in (i) above; plus
iv) 25% of the sum of the calculated loads in the next 15 units having the same or next smaller loads
to those specified in (i) above; plus
ETHIOPIAN BUILDING CODE STANDARD
EBCS-10: 2013
SECTION 6: CIRCUIT LOADING AND DEMAND FACTOR
v) 10% of the sum of the calculated loads in the remaining units;
(b) If air-conditioning is used, the amount by which the sum of all the air-conditioning loads exceeds
1500.0V A shall be added, with a demand factor of 100%, to the load determined in accordance
with (a) above.
(c) In addition, any lighting, heating, and power loads not located in dwelling units shall be added with
a demand factor of 75%.
Note: The living area designated in Clause 6.5.1 and 6.5.2 shall be determined from the outside dimensions of the
group floor of the dwelling plus 75% of the basement area based on the inside dimensions, plus any area
which might normally be used for living purposes on the upper floors.
6.5.3 Schools
(l) The minimum ampacity of service or feeder conductors shall be based on the following:
a) a basic load of 50.0W/m2 of classroom area; plus
b) 10.0W/m2 of the remaining area of the building based on the outside dimensions; plus
c) air conditioning, and power loads based on the rating of the installed equipment.
(2) Demand factors may be applied as follows:
(a) 75% for a building with an area up to and including 900.0m2 based on the outside dimensions.
(b)
For a building with an area exceeding 900.0m2 based on the outside dimensions, the load may,
be divided by the number of square meters to obtain a load-pre-square-meter rating and the
demand load may be considered to be the sum of:
i) 75% of the load per square meter multiplied by 900; and
ii) 50% of the load per square meter multiplied by the area of the building in excess of 900.0m2
6.5.4 Hospitals
(1) The minimum ampacity of service or feeder conductors shall be based on the following:
(a) a basic load of 20.0W/m2 of the area of the building based on the outside dimensions; plus
(b) 100.0W/m2 for high intensity area such as operating rooms; plus
(c) air conditioning, and power loads based on the rating of the installed equipment
(2) Demand factors may be applied as follows:
ETHIOPIAN BUILDING CODE STANDARD
EBCS-10: 2013
SECTION 6: CIRCUIT LOADING AND DEMAND FACTOR
80% for a building with an area up to and including 900.0m2 based on the outside dimensions;
(a)
(b)
For a building with an area exceeding 900.0 m2 based on the outside dimensions, the balance of
the load may be divided by the number of square meters to obtain a load-per square- meter rating
and the demand load may be considered to be the sum of:
i) 80% of the load per square meter multiplied by 900; and
ii) 65% of the load per square meter multiplied by the area of the building in excess of 900.0m2
6.5.5 Hotels, Motels, Dormitories, and Buildings of Similar Occupancy
(1) The minimum ampacity of service or feeder conductors shall be based on the following:
(a) a basic load of 20.0W/m2 of the area of the building based on the outside dimensions; plus
(b) lighting loads for special areas such as ballrooms; based on the rating of the equipment installed;
plus
(c) air conditioning and power loads based on the rating of the equipment installed.
(2) Demand factors may be applied as follows:
(a) 80% for a building with an area up to and including 900.0m2 based on the outside dimensions;
(b)
For a building with an area exceeding 900.0m2 based on the outside dimensions, the balance of
the load may be divided by the number of square meters to obtain a load-per square-meter rating
and the demand load may be considered to be the sum of:
i) 80% of the load per square meter multiplied by 900; and
ii) 65% of the load per square meter multiplied by the area of the building in excess of 900.0m2
6.5.6 Other Types of Occupancy
(1) The minimum ampacity of service of feeder conductors for the types of occupancies specified in Table
6.1 shall be based on the following:
(a) a basic load to be calculated on the basis of watts per square meter required by Table 6.1 for the
area served based on the outside dimensions, with application of demand factors as indicated
therein; plus
(b) special loads such as air conditioning, power loads, show window lighting, stage lighting, etc,
based on the rating of the equipment installed with such demand factors as are permitted by this
Code.
ETHIOPIAN BUILDING CODE STANDARD
EBCS-10: 2013
SECTION 6: CIRCUIT LOADING AND DEMAND FACTOR
6.5.7 Branch Circuits
(1) Conductors of a branch circuit supplying "Injera Mitad" and/or cooking stove in a dwelling unit shall
be considered as having a demand of
(a) 3.5kW for "Injera Mitad";
(b) 8.0kW where the rating of the cooking stove does not exceed 12.0kW; or
(c) 8.0kW.plus 40% of the amount that the rating of the cooking stove exceeds 12.0kW.
Note: For the purpose of Clause 6.5.7(1), two or more separate built-in cooking units may be considered as one
Cooking
(2) For "Injera Mitadn and or a cooking stove installed in commercial, industrial, and institutional
establishments, the demand shall be considered as not being less than the rating.
(3) The demand loads given in (1) above shall not apply to cord-connected hotplates or other appliances.
6.5.8 Feeder Demand Factors for Lifts
(1) Feeder demand factors for lifts shall be as shown in Table 6.2.
ETHIOPIAN BUILDING CODE STANDARD
EBCS-10: 2013
SECTION 6: CIRCUIT LOADING AND DEMAND FACTOR
Table 6.1 Demand factor for service and feeders and watts per square meter for
various types of occupancy
Type of Occupancy
Watts per
m2
Demand factor [%]
Service
conductor
Feeders
Store, Restaurant
30
100
100
Office
50
70-90
90
Industrial and Commercial
25
100
100
Church/Mosque
10
100
100
Garage
10
100
100
Storage warehouse
5
70
90
Theatre
30
75
95
Armories and Auditoriums
10
80
100
Banks
50
100
100
30
90
100
Clubs
20
80
100
Court houses
20
70
90
Lodges
15
80
100
Barber shops and
parlors
beauty
ETHIOPIAN BUILDING CODE STANDARD
EBCS-10: 2013
SECTION 6: CIRCUIT LOADING AND DEMAND FACTOR
Table 6.2 Feeder demand factors for lifts
Number of lifts
on a single
feeder
Demand factors (DF)
Number of lifts on a
single feeder
Demand factors (DF)
1
1.00
6
0.79
2
0.95
7
0.77
3
0.90
8
0.75
4
0.85
9
0.73
5
0.82
10 or more
0.72
Note: Demand factors (DF) are based on 50% duty (i.e, half-time load, half-time no load).
ETHIOPIAN BUILDING CODE STANDARD
EBCS-10: 2013