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Security device coordination

RCD, as an element of an electric circuit, must be protected from overload and short circuit current by a series protective device (ROM).

GOST 50571.5-94 defines in paragraph 433:

  • “Protection devices shall disconnect any overload current flowing through the conductors earlier than such current could cause an increase in the temperature of the conductors, which is dangerous for insulation, connections, clamps or the environment surrounding the conductors."
  • The rated operating current of the RCD must be equal to or one step (from a number of standard values ​​of the rated currents of the RCD) higher than the rated operating current of the ROM.

GOST R 50807-95 states:

  • 2.4.8. Short-circuit protection device specified by the manufacturer, which must be installed in series with the RCD in order to protect against short-circuit currents.
  • 4.3.1. The short circuit protection device is designed to provide sufficient protection for RCDs from the effects of short circuit currents not exceeding the nominal nominal short circuit current I nc and the nominal differential differential short circuit current I D c .

The manufacturer of the RCD must indicate the following characteristics of the short circuit protection device:

a) the maximum value of the passed value I 2 t;

b) the maximum value of the transmitted peak current I p .

If the manufacturer does not specify these values ​​for the RCD, then the minimum values ​​are taken depending on the conditional short-circuit current from the table. 4.1.

Any short circuit protection device that meets the requirements established by the relevant standard and has the characteristics of a) and b), not exceeding the values ​​specified by the manufacturer for the RCD, can be used to protect the RCD.

GOST R 51326.1-99 contains the following requirement:

  • 9.11.2. The RCD must be protected against short circuit by means of circuit breakers or fuses in accordance with the requirements of the relevant standards of the GOST R 50571 series.
  • The ROM may be a circuit breaker or fuse having a Joule integral I 2 t and peak current I p not exceeding the ability to withstand I 2 t and I p set for the RCD by the manufacturer.

The Russian standard GOST R 50345-92 (IEC 898-87) "Circuit breakers for protection against household and similar circuit-breakers" classifies circuit breakers by instantaneous trip current: types B, C and D.

The time-current performance of circuit breakers of types B, C and D is shown in Fig. 10.1.

Time-current performance of circuit breakers type B, C and D

Figure 10.1. Time-current performance of circuit breakers type B, C and D