SECTION 8:ELECTRIC MOTORS, MOTOR CIRCUITS AND CONTROLLERS
SECTION 8
ELECTRIC MOTORS, MOTOR CIRCUITS AND CONTROLLERS
801 All motors shall generally be totally enclosed, fan-cooled Other types of enclosures may be employed provided that they are suitable for the particular application.
802 All motors, control gears and all ancillary apparatus (e.g. remote push buttons, pressure, float or limit switches, interlocks, relays, etc.) shall be of robust construction and shall have all windings, contacts and all current carrying live parts and components insulated with suitable materials. For certain applications and locations other superior classes of insulating materials may be applicable, and each situation shall be carefully studied in order to ensure that the temperature rise of the motor as declared by the manufacturer + ambient temperature is at least 10آ°C below the maximum operating temperature of the insulating material used.
NOTES:
- The ambient temperatures in plant rooms should be taken as 55آ°C.
- In all cases where the motors depend totally on the outside air for cooling whether by natural ventilation or by mechanical ventilation of the motor room, the entering cooling air temperature shall be taken as not less than 48آ°C for the purpose of calculating the amount of ventilating air.
803 Motors and their control gears shall be located so that adequate ventilation is provided and so that inspection and maintenance can be readily accomplished.
804 If any motor is to be located out of doors, such motor shall be protected from over heating by the sun with a canopy of approved design.
805 Motors below 1 H.P. (0.75 KW) may be connected to single phase supply. Under special conditions to be approved by EDD for each individual case, motors upto 5 H.P. (3.75 KW) may be connected to single phase supply. No motor higher than 5 H.P. (3.75 KW) shall be connected to single phase.
806 Self-contained air conditioning units upto 2.5 KW may be connected to a single phase supply.
807 Motors upto 150 H.P. (1 12 KW) may be connected to the 400 volts supply system. Where a consumer proposes to use motors of higher capacity, he should contact the EDD to obtain the approval of such supply before purchasing any motor or appliance. If power supply at voltages higher than 400 volts are required, EDD can only supply 11000 volts, 3 phase, 5OHz.
808 3 -Phase motors upto and including 5 H.P. (3.75 KW) may be started direct on line (D.O.L.). motors above 5 H.P. (3.75 KW) shall be provided with equipment to ensure that starting current does not exceed 2.5 time the full load current. For larger motors, method of starting and voltage dips must be discussed with and approved by EDD in each case before the motors are connected to power supply.
809 All motors over 1 H.P. (O.75 KW) shall be provided with starters which have means for automatically disconnecting them from the electric supply in the event of Failure of supply, Serious drop in voltage, Flow of excess current
EXCEPTION: For motors driving fire pumps, the above protections may be omitted. Where no volt releases are fitted to such motors they shall be of the automatic resetting type.
810 Each motor over 1 H.P. (0.75 KW) shall be provided with means of isolation suitably placed and so connected that all voltage may be cut off from the motor and a lockable all apparatus including any automatic circuit breaker used therewith. If this means of isolation is remote from a motor, an additional means of isolation adjacent to the motor shall be installed. This means of isolation may be an isolator or "stop-lock" button.
811 Where a group of motors function as one unit, means shall be provided in the control system, to prevent the simultaneous starting of all motors at one and the same time. Where this is not possible for any reason whatsoever, the method of starting shall be approved by the E.D.D.
812 Starters shall be provided with overload relays of the thermal or hydraulic type with automatic compensation for variation in ambient temperature between Oآ°C and 55آ°C.
813 All starters and push buttons shall be clearly labelled in Arabic and English stating the machines they control and the function of the various buttons.
STOP push buttons shall have large mushroom heads and/or coloured bright red.
START push buttons shall be shrouded to prevent accidental operation and must be coloured green.
814 All motors, single phase and three phase, shall have a power factor according to clause 313 at full load. Final circuit conductor sizes for motors shall be selected in accordance with the method indicated in Section 14.
815 All motors shall be suitably earthed in accordance with the requirements set out in Section 6. A frame earth terminal shall be provided in addition to the terminal block earth.
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