Contacts indirects

Stéphane DANTIGNY

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Indirect contact is contact between a physical person and a conductive part accidentally energized. This is, for example, contact with a metal cabinet that is not earthed and whose electrical equipment it contains has an insulation fault.
In this case, part of the leakage current passes through the human body.
One of the measures to protect against indirect contacts is the protection measure by automatic cut-off of the supply to the outgoing circuit breaker concerned.

This measure is based on the combination of two conditions:

- the constitution of a fault loop allowing the circulation of a fault current: this fault loop requires the implementation of protective conductors connecting the masses of the electrical equipment either to an earth connection (TT, IT system) , or at the neutral point of the power supply (TN regime) ;
- interruption of the fault current by a protection device in a time compatible with the safety of persons.

It is checked that the maximum length of the conductors which form the fault loop ensures the tripping of the protection device against insulation faults (magnetic protection on a circuit breaker)