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Section 3. Protection and automation
Protection of electrical networks with voltage up to 1 kV. Requirements for protective equipment
Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)
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3.1.3. Protection devices, in terms of their breaking capacity, must correspond to the maximum value of the short-circuit current at the beginning of the protected section of the electrical network (see also chapter 1.4).
It is allowed to install protection devices that are unstable to the maximum values of short-circuit current, as well as selected by the value of a one-time limiting switching capacity, if the group device protecting them or the nearest device located towards the power source provides instantaneous disconnection of the short-circuit current, for which it is necessary that the current the settings of the instantaneous release (cut-off) of these devices was less than the current of the one-time switching capacity of each of the group of unstable devices, and if such a non-selective shutdown of the entire group of devices does not threaten an accident, damage to expensive equipment and materials or disrupt a complex technological process.
3.1.4. Rated currents of fuse links and setting currents of automatic switches used to protect individual sections of the network should in all cases be chosen as low as possible according to the rated currents of these sections or according to the rated currents of electrical receivers, but in such a way that protection devices do not turn off electrical installations during short-term overloads (starting currents, process load peaks, self-starting currents, etc.).
3.1.5. Circuit breakers or fuses should be used as protection devices. To ensure the requirements of speed, sensitivity or selectivity, it is allowed, if necessary, to use protection devices using remote relays (indirect relay).
3.1.6. Circuit breakers and plug-type fuses must be connected to the network so that when the plug of the fuse (circuit breaker) is unscrewed, the screw sleeve of the fuse (circuit breaker) remains without voltage. With a one-way supply, the connection of the supply conductor (cable or wire) to the protection device should, as a rule, be carried out to fixed contacts.
3.1.7. Each protection device must have an inscription indicating the values of the rated current of the device, the setting of the release and the rated current of the fuse-link required for the network it protects. Inscriptions are recommended to be applied on the device or circuit located near the place of installation of protection devices.
 See other articles Section Rules for the installation of electrical installations (PUE).
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