SECTION 9: PROTECTION AND CONTROL
SECTION
9
PROTECTION AND CONTROL
9.1 SCOPE
(1) This Section covers the protection and control of electrical circuits and apparatus installed in
accordance with the requirements of this Code.
9.2 NORMATIVE REFERENCES
(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
(b) BS 7671:2001
Canadian Electrical Code Part I, Safety Standard for Electrical Installation,
Nineteenth Edition.
Requirements for Electrical Installation, IEE Wiring Regulations,
Sixteenth Edition.
(c ) NFPA 70 / NEC: 2008 American National Fire Protection Association/ National Electrical
Code, 2008 Edition
9.3 GENERAL REQUIREMENTS
9.3.1 Protective and Control Devices
(1) Every electrical apparatus and unearthed conductors shall be protected by one or more devices as may
be necessary for automatic and/or manual interruption of the supply in the event of any fault and shall be
provided with:
(a) protection against fault current to break any fault current in a circuit before such current causes
danger due to thermal or mechanical effects produced in those conductors or the associated
connection;
(b) protection against overload current to break any such current flowing in the circuit conductors
before such a current causes a temperature rise detrimental to insulation, joints, termination or the
surroundings of the conductors;
(c) protection against under-voltage which when necessary will open the circuit, where a reduction in
voltage, or loss and subsequent restoration of voltage could cause danger;
(d) manually-operable control device which will safely disconnect all unearthed conductors of the
circuit at the point of supply simultaneously; and
ETHIOPIAN BUILDING CODE STANDARDS
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SECTION 9: PROTECTION AND CONTROL
(e) protection against earth fault in accordance with Clause 9.4.2.
9.3.2 Types and Ratings of Protective and Control Devices
(1) Circuit breakers, fuses, and switches shall be of type and ratings acceptable to the department in
charge of inspection.
(2) Overcurrent protective devices shall ensure safe operation and shall have interrupting capacity
sufficient for the voltage employed and for the anticipated fault current which must be interrupted.
9.4 Protective Devices
9.4.1 Overcurrent Devices
(1) Each unearthed conductor shall be protected by an overcurrent device at the point where it receives its
supply of current and at each point where the size of conductor is decreased, except that such protection
may be omitted where:
(a) the overcurrent device in a larger conductor properly protects the smaller conductor;
(b) the smaller conductor is not over 3.0m long and does not extend beyond the switchboard, panel
board, control device which it supplies; or
(c) the smaller conductor has an ampacity not less than one-third that of the larger conductor from
which it is supplied.
(2) The rating or setting of overcurrent devices shall not exceed the allowable ampacity of the conductors
which they protect except:
(a) where a fuse or circuit breaker having a rating or setting of the same value as the ampacity of the
conductor is not available, the ratings or settings given in Table 9.1 may be used;
(b) in case of equipment wire, flexible cord, and tinsel cord, which will be considered as being
protected by 16.0A overcurrent devices; or
(c) as provided for by other Clauses of this Code.
(3) Overcurrent devices shall be enclosed in cutout boxes or cabinets unless they form a part of an
approved assembly which affords equivalent protection, or unless mounted on switchboards, panel
boards, or controllers located in room or enclosures free from easily ignitable material and dampness, and
accessible only to authorized persons.
(4) Overcurrent devices shall not be connected in parallel in circuits of 1000.0V or less unless otherwise
they are factory-assembled in parallel as a single unit.
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SECTION 9: PROTECTION AND CONTROL
9.4.2 Earth-Fault Protection
(1) Earth-fault protection shall be provided to de-energize all normally earthed conductors of a faulted
circuit in the event of an earth fault in those conductors as follows:
(a) in solidly earthed circuits rated more than 230.0V-to-earth, less than 1000.0V phase-to phase and
1000.0A or more; and
(b) in solidly earthed circuits rated 230.0V-to-earth or less and 2000.0A or more.
(2) The maximum setting of the earth-fault protection shall be l200.0A and the maximum time delay shall
be 1.0s for earth fault currents equal to or greater than 3000.0A.
(3) The ampere rating of the circuits referred to in (1) above shall be considered to be:
(a) the rating of the largest fuse that Can be installed in a fusible disconnecting device;
(b) the highest trip setting for which the actual overcurrent device installed in a circuit breaker is
rated or can be adjusted; or
(c) the ampacity of the main conductor feeding the devices in cases where no main disconnecting
device is provided.
(4) Earth-fault protection shall be provided by:
(a) an overcurrent device which incorporates earth-fault protection;
(b) earth-fault trippi.ng system comprising a sensor sensors, relay and auxiliary tripping mechanism;
or
(c) other appropriate means.
9.5 Fuses
(1) Only fuses and fuse holders of proper rating shall be used, and no bridging or short circuiting of either
component shall be permitted.
(2) Where plug fuses are used in branch circuits, they shall be of such a type and so installed that they are
non-interchangeable with a fuse of larger rating.
(3) A fuse having a fuse link which is likely to be removed or replaced while the supply is connected shall
be of a type such that it can be removed or replaced without danger.
9.6 Circuit Breakers
(1) Circuit breakers shall be of the trip-free type.
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SECTION 9: PROTECTION AND CONTROL
(2) Indication shall be provided at the circuit breaker and at the point of operation to show whether the
circuit breaker is open or closed.
(3) Circuit breakers shall open the circuit in all unearthed conductors by the manual operation of a single
handle and by the action of overcurrent.
(4) Circuit breakers shall be of such design that any alteration by the user of either the tripping current or
the time will be difficult.
(5) Circuit breakers shall be equipped with tripping elements as specified in Table 9.2.
9.7 control devices
(1) Control devices shall have ratings suitable for the connected load of the circuits which they control
and, with the exception of isolating switches, shall be capable of safely establishing and interrupting such
loads.
(2) Control devices used in combination with overcurrent devices or overload devices for the control of
circuits or apparatus shall be connected so that the overcurrent or overload devices will be dead when the
control device is in the open position, except where this is impracticable.
(4) Control devices, unless located or guarded so as to render them inaccessible to unauthorized persons
and to prevent fire hazards, shall have all current-carrying parts in enclosures of metal or other fireresisting material.
(5) Where electrical equipment is supplied by two or more different transformers or other sources of
voltage, then:
(a) a single disconnecting mean~, which will effectively isolate all unearthed conductor supplying
the equipment, shall be provided integral with or adjacent to the equipment; or
(b) each supply circuit shall be provided with a disconnecting means integral with or adjacent to the
equipment, and the disconnecting means shall be grouped together.
9.8 switches
(1) Single-throw knife switches shall be mounted with their bases in a vertical plane so that gravitational
force will not tend to close them.
(2) (a)
Double-throw knife switches may be mounted so that the throw will be either vertical or
horizontal.
(b)
If the throw in (1) above is vertical, a positive locking device or stop shall be provided to
ensure that the blades remain in the open position when so set unless it is not intended that the
switch be left in the open position.
(3) Manual single-throw switches, circuit breakers, or magnetic switches, shall be connected so that the
bases or moving contacts will be dead when the device is in the open position except when other
conditions make this requirement unnecessary.
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SECTION 9: PROTECTION AND CONTROL
9.9 Protection and Control of Miscellaneous Apparatus
(1) Socket outlets shall not be connected to a branch circuit having overcurrent protection rated or set at
more than the ampere rating of the socket outlets except as permitted by other Sections of this Code.
(2) Portable appliances need not be equipped with additional control devices where the appliances are (3)
Control devices, with the exception of isolating switches, shall be readily accessible.
(a) rated at not more than 1500.0W; and
(b) provided with cord connectors, attachment plugs or other means by which they can be
disconnected readily from the circuits.
(3) Where switches are used to control an outlet or outlets from more than one point, the switches shall be
wired and connected so that the earthed conductor runs directly to the outlet or outlets controlled by the
switches.
(4) Except for panel boards where more than 90% of the overcurrent devices supply feeders or motor
branch circuits, every panel board shall be protected on the supply side by overcurrent devices having a
rating not greater than that of the panel board.
(5) Transfer equipment for standby power systems shall prevent the inadvertent interconnection of normal
and standby sources of supply in any operation of the transfer equipment.
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SECTION 9: PROTECTION AND CONTROL
Table 9.1 Rating or setting of overcurrent devices protecting conductors
(For general use where not otherwise specifically provided for)
Rating or setting permitted [A]
Ampacity of Conductors
Fuse
Circuit breaker
0-16
16
16
17-22
20
20
21-25
25
32
26-32
32
32
33-40
40
40
41-50
50
50
51-63
63
63
64-80
80
100
91-100
100
100
101-110
110
125
111-125
125
125
126-150
150
150
151-175
175
175
176-200
200
200
201-225
225
225
226-250
250
250
251-275
300
300
276-300
300
300
301-325
350
350
326-350
350
350
351-400
400
400
401-450
450
450
451-500
500
500
501-525
600
600
526-550
600
600
551-600
600
600
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SECTION 9: PROTECTION AND CONTROL
Table 9.2 Overcurrent trip coils for circuit breakers and overload devices for protecting motors
For circuit protection†
Number and location of
overcurrent devices (Trip Coils)
For motor overload protection
System
3-trip coils, one in each
conductor
3-wite, 3-phase a.c., unearthed or with
earthed neutral
3-trip coils, one in each phase
4-wire, 3- phase a.c
2-trip coils, one each phase
4-wire, 2-phase a.c., unearthed
Number and location of overload
devices such as trip coils relays, or
thermal cutouts
Kind of motor
3
one in each phase not to
be connected in any
neural conductor
3-phase a.c.
2
one in each phase, not be
connected in any neutral
or earthed conductor
2-phase a.c.
1
in any conductor except a
neutral or earthed
conductor
1-phase a.c. or d.c
2-trip coils, o ne in each outside 3-wore, 2-phase a.c.
conductor
4-trip coils, one in each
unearthed conductor
4-2ire, 2-phase a.c., with earthed neutral
4-trip coils, one in each
unearthed conductor
5-wire, 2-phase a.c.
2-trip coils, one in each outside
3-wire, 1-phase a.c. or d.c.
1-trip coil in each unearthed
conductor
2-wire a.c. or d.c., unearthed or with
one conductor earthed††
2-trip coils, one in each
unearthed conductor
3-wirie, 1-phase a.c. or d.c., with
earthed neutral
†
This will not preclude the use of other arrangements which will provide equivalent protection.
This will not prevent the use of one single-pole circuit breaker in each conductor for the protection of an unearthed 2-wire circuit.
††
ETHIOPIAN BUILDING CODE STANDARDS
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