IEEE C37.21a-2020 pdf free download

IEEE C37.21a-2020 pdf free download.IEEE Standard for Control Switchboards Amendment 1: Control and Secondary Circuits and Devices, and All Wiring.
7.1.5.1 General
All voltage circuits used for control, relaying, or metering shall be protected within the switchboard as follows:
a) All circuits supplied from external sources (ac or dc) shall have short-circuit protection. This may be provided by a single set of short-circuit protective devices within the control source incoming section.
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 be 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.
Qrercurrcnt protection of current transformer secondary circuits shall not be provided. Open circuit protection should he considered where current transformer wiring connects to devices external to the switchboard assembly.
Primary and secondary protective devices may be omitted from voltage-dividing devices such as capacitive and resistive voltage dividers.
7.1.5.2 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 sufTiciently 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.
Replace 7. 1.5.3 (formerly known as 7.1.5.1), iiicluding all suhclause as shown:
7.1.5.3 Control, secondary, and logic level wiring
Flame-retardant, 600 V insulated stranded copper wire shall be used for internal wiring between components of switchboard 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 switchgear loads is not covered by this clause.
The switchboard manufacturer is responsible for the pcrlbrmancc of the wiring system provided by the manufacturer within the switchboard.IEEE C37.21a-2020 pdf free download.