MCB RCBO and AFDD What Each Device Actually Protects

What an MCB Does

A miniature circuit breaker protects the cable against overload and short circuit. It reacts to current magnitude, thermally for a sustained overload and magnetically for a short circuit. Our AC range is built to GB10963.1 and IEC60898-1 with a Type C characteristic. What an MCB does not do is notice current leaking to earth, or an arc drawing normal current.

What an RCBO or RCCB Adds

A residual current device compares the current flowing out with the current returning. A difference means current is leaking, usually through a person or through damaged insulation. An RCCB provides only that function, an RCBO combines it with overcurrent protection in one device. In this range that is the RCCB, RCBO and ELCB family, including the DZ47LE-63, HTB2L-80 and HTB2LE-40 models.

What an AFDD Detects

An arc fault draws current that can look entirely normal to both an MCB and an RCD. A loose terminal or a crushed flex produces an intermittent arc which generates heat at the fault point. An AFDD analyses the current signature and disconnects when it recognises an arc. Our AFDD models work at 230V 50Hz to IEC62606, including a 32A adjustable device.

Choosing Between Them

Cable protection is the MCB. Shock and earth leakage protection is the RCCB or RCBO. Fire risk from damaged wiring is the AFDD. On a circuit with old wiring feeding valuable contents all three functions are relevant, which is why AFDD and RCBO combination devices exist.

Testing the Installation

Residual current devices have a test button. Arc fault protection is harder to prove on site, which is why we supply an arc fault electric test device that generates a controlled arc so the AFDD can be demonstrated at commissioning.