Will a short circuit in the power cord causing a fire trigger the leakage protector?
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If the electrical device is a single-phase device, a single-phase two-conductor wire (Category 2 tool) is used; in such a case, a short circuit between the phase wire and the neutral wire can cause the power cable to catch fire. Will the residual current device operate at this time? If the electrical device is a three-phase device that uses a three-phase four-wire system without a protective neutral wire, all four wires are connected to the leakage protector. When a phase-to-phase short circuit occurs and the upstream circuit breaker does not operate, will the leakage protector activate? Residual current devices do not provide protection against electric shock hazards caused by two wires in the circuit being protected. ____How should this sentence be understood? This post was last edited by yuekw on 2008-1-17 02:31.]
Under normal conditions, when there is no electric shock to persons, no leakage current in the equipment, and no grounding faults in the circuit, the vector sum of the currents in the primary side circuit of the current transformer for the residual current protection device is equal to zero, that is, IL1 + IL2 + IL3 + IN = 0. As a result, the vector sum of the magnetic fluxes generated by the currents IL1, IL2, IL3, and IN in the current transformer is also equal to zero, that is, FL1 + FL2 + FL3 + FN = 0. Consequently, no induced voltage is generated in the secondary coil of the current transformer, and thus the residual current protection device maintains normal power supply. When there is an electric shock to a person in the circuit, equipment leakage, or faulty grounding, a grounding current IN flows through the equipment’s grounding resistance RA. As a result, the vector sum of the currents passing through the transformers is not zero: IL1 + IL2 + IL3 + IN ≠ 0. The vector sum of the magnetic fluxes generated in the residual current transformers is also not zero, that is, FL1 + FL2 + FL3 + FN ≠ 0. An induced voltage is generated in the secondary circuit of the transformers; this voltage is applied directly or via an electronic signal amplifier to the trip coil, thereby generating an operating current. The induced voltage output of the secondary circuit increases as the fault current rises; when the ground fault current reaches its rated value, the current in the trip coil is sufficient to activate the trip mechanism, thereby breaking the circuit through the main switch or triggering an alarm signal from the alarm device. Therefore, an electric shock caused by the second wire within the protected circuit does not generate a residual current, and as a result, no protection action is triggered. A typical residual current device combines overload and short-circuit protection, and can take action to protect against short circuits at the output side (a standalone residual current protector does not have this function). Single-phase residual current devices and three-phase residual current devices operate on the same principle
Agree with the person above. That is, if there is a short circuit and your circuit breaker has a high rating, it won’t trip. I’ve encountered situations where a 400A DZ20 circuit breaker wasn’t triggered even when a 4*4 cable connected downstream suffered a short circuit and caught fire