Coordination of protection devices

RCD, as an element of the electrical circuit shall be protected against overload and short-circuit serial protection device (ROM).

GOST 50571.5-94 defines in clause 433.:

  • "Safety devices must disable any overload current flowing through the conductors before such a current could cause a rise in temperature conductors, dangerous for the insulation, connections, clamps or the environment surrounding the wires."
  • Rated operating current RCD should be equal to or one rank (out of the standard value of the rated current of RCD) above the nominal operating current ROM.

In GOST 50807-95 is specified:

  • 2.4.8. Protection against short-circuit, the manufacturer, which must be installed in series with the RCD to protect against short-circuit currents.
  • 4.3.1. Protection device against short circuits is designed to provide adequate protection from exposure to the RCD short circuit, do not exceed the rated conditional short-circuit current I nc and rated conditional short-circuit residual current I D c.

The manufacturer shall specify the following RCD protection device characteristics of short-circuit:

a) the maximum value of I skipped 2 t;

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

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

Any protection device against short-circuits, which meets the requirements established by the relevant standard and has the characteristics of n. A) and para. B), does not exceed the value specified by the manufacturer for the RCDs can be used for the protection of the RCD.

The GOST R 51326.1-99 contains the following requirement:

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

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

Time-current operating characteristics of circuit breakers type B, C and D are shown in Fig. 10.1.

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

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