9. Select the type and parameters of the RCD
9.4. Nominal disconnecting differential current I D n (setting)
Rated residual current I D n - current setpoint is chosen from the following series: 6, 10, 30, 100, 300, 500 mA
Setting RCD for each particular application is chosen based on the following factors:
- the value of the existing electrical installation in the total (including the merging of fixed and portable power consumers) leakage current to the ground - the so-called "background leakage";
- the permissible current through a person on the basis of electrical safety criteria;
- the real value of the differential current tripping the RCD, which is in accordance with the requirements of GOST 50807-94 is in the range 0,5 I D n - I D n .
According to the requirements of the SAE (.. 7th ed, p 01/07/83) nominal differential RCD tripping current should be not less than three times the total leakage current of the protected electrical circuit - I D.
I D n> = 3 I D.
The total electrical leakage current is measured by special devices (Appendix 4) or determined by calculation.
In the absence of the actual (measured) values of the leakage current in the electrical installation of the SAE (p. 7.1.83) are required to take the leakage current of power consumers at the rate of 0.4 mA to 1A load current, and the circuit leakage current at 10 uA per 1 m length of the phase conductor .
Recommended values of the rated residual operating current - I D n (set point) for a range of RCD rated currents of 16 A to 80 are given in Table. 9.2.
Table 9.2.
| Rated load current in the protection zone | 16 | 25 | 40 | 63 | 80 |
| I D n at work in the protection zone of a single customer, mA | 10 | thirty | thirty | thirty | 100 |
| I D n when working in the area of protection of consumers groups, mA | thirty | thirty | 30 (100) | 100 | 300 |
| I D n RCD fire-fighting purposes at ASU, mA | 300 | 300 | 300 | 300 | 300 |
In some cases, for certain consumers setpoint is defined by normative documents. In GOST 50669-94 for buildings of metal or with a metal frame is set RCD setting no higher than 30 mA.
Temporary instructions prescribe: Sanitary cabins, bathrooms and showers installed RCD tripping current:
- 10 mA, if they are allocated a separate line; in other cases (for example, using one line for sanitary cabins, kitchens and corridors) may be used RCD with a 30 mA setpoint (4.15 p.);
- in individual homes for group circuits supplying sockets inside the house, including basements, built-in and attached garage as well as in the group networks that feed the bathrooms, showers and saunas with RCD setting 30 mA;
- for externally mounted sockets with RCD setting 30 mA (Sec. 6.5).
The PUE (7 th ed. P. 7.1.84) is recommended to increase the level of protection against fire-fault grounded parts on entering the apartment, individual house, etc. installation of RCDs with tripping current of 300 mA.
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