Basic Design And Method Of Operation; Type A Rccb - Siemens SENTRON Manual

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4.3

Basic design and method of operation

4.3.1

An RCCB of Type A essentially consists of the following function groups:

• Summation current transformer for detecting residual current

• Tripping circuit with components for evaluation and holding magnet release for

converting the electrical measured variable into a mechanical latch release

• Breaker mechanism with contacts

Note

With the exception of the tripping circuit, the design of the Type AC and

Type F RCCBs is identical to that of Type A.

The summation current transformer comprises all conductors of the circuit to be

protected, including the neutral conductor. In a fault-free system, the magnetic

effects of the current-carrying conductors are canceled out in the summation

current transformer. There is no residual magnetic field which could induce

voltage onto the secondary winding of the transformer.

A residual magnetic field remains in the transformer core only if residual current

is flowing, e.g. due to an insulation fault in the system to be protected (from the

electrical point of view, downstream of the RCCB). This generates a voltage in the

secondary winding, effecting disconnection of the circuit with the excessive touch

voltage by means of the holding magnet release and the breaker mechanism

(see Fig. 5).

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