IEEE Std C37.20.2a-2020 pdf download

IEEE Std C37.20.2a-2020 pdf download.IEEE Standard for Metal-Clad Switchgear Amendment 1: Control and Secondary Circuits and Devices, and All Wiring.
b) All circuits supplied from internal sources (ac or dc) circuits shall have short-circuit protection within the same section as the supply source. If these circuits are supplied by a control power transformer, this protection may he in the primary circuit only.
c) Overcurrent protection of voltage circuits may be provided in addition to the required short-circuit protection.
d) Other circuits supplying loads, such as heaters, receptacles, and lights, shall have overload and short-circuit protection.
Overcurrent protection of current transformer secondary circuits shall not be provided. Open circuit protection should be considered where current transformer wiring connects to devices external to the switchgear assembly.
Primary and secondary protective devices may be omitted from voltage-dividing devices such as capacitive and resistive voltage dividers.
7.3.2 Voltage transformer fusing
The following requirements shall be met:
a) Primary circuits of all voltage transformers shall include current-limiting fuses.
b) Secondary circuits of all voltage transformers shall include fuses or their equivalent.
EXCEPTION: Fuses may be omitted from secondary circuits of voltage transformers if the secondary burden includes voltage regulators, protective relays, or other devices considered sufficiently essential to the operation of’ the installation to make it preferable to incur the hazards associated with the possible destruction of the voltage transformer by a sustained secondary short-circuit rather than to risk interruption of the voltage supply to such devices as a result of a momentary secondary short-circuit.
7.3.3 Control, secondary, and logic-level wiring
Flame-retardant, 600 V insulated stranded copper wire shall be used for internal wiring between components of switchgear assemblies, and to terminals for connection to external controls, metering, or instrumentation. Wiring within components is assumed to be covered by standards applicable to those devices and is not covered by this standard. Wiring for the purpose of conveying power to external switchgcar loads is not covered by this clause.
The switchgear manufacturer is responsible for the performance of the wiring system provided by the manufacturer within the switchgear. This applies to the integrity of internally generated signals in the control wiring, and may require the use of special precautions such as shielded wire, twisted-pair wire, or segregation of certain wires.
7.3.3.1 Wiring across a hinge
Wiring that crosses a hinge shall be suitable for this use, as defined by all of the following criteria:
a) Wire shall be sized according to 7.3.3.2.
b) Single conductors shall be stranded wire.
c) Wire shall be sufficiently flexible to withstand repeated door movement without sustaining damage to wire strands or insulation.
d) The loop formed by the wiring as it crosses the hinge shall be secured to the equipment at both ends, in such a manner that negligible strain is transmitted to wire beyond the securernents to prevent damage to the wire insulation as the door is moved.
e) Wiring shall not prevent the door from opening to the intended maximum opening, with a minimum opening of 90 degrees.
f) The wire loop is to be protected between the securements to provide a degree of protection against damage to the wire insulation as the door is moved.
g) No sharp edges or objects are allowed in the path swept by the wire loop as the door is operated.
h) If the wire is No. 14 AWG or larger wire, the wire shall be no less flexible than Class C or D stranding.
7.3.3.2 Wire size
Wire shall be suitable for the anticipated maximum steady-state load. The size chosen should also accommodate voltage drop within the switchgear, including the effect of intermittent heavy loads (shunt trip coils, inrush from relays, and the like). The following criteria shall be used as minimums.