Dispositivo de corriente residual
Un dispositivo de corriente residual (RCD) o un interruptor de circuito de falla a tierra (GFCI) es un dispositivo que mide constantemente la corriente que fluye entre los cables de entrada y salida de un circuito para ver si hay una diferencia. Si hay una diferencia, significa que hay una falla en algún punto del circuito y un peligro potencial. Por lo general, un RCD se incorpora un interruptor automático o tomacorriente para que pueda desconectar el circuito al identificar una diferencia en la corriente o una falla. Los RCD a menudo son requeridos por los códigos eléctricos en muchos países. En un sistema puesto a tierra, esta corriente normalmente regresa a través del sistema de puesta a tierra. Los RCD son mucho más efectivos para prevenir accidentes eléctricos que los DPCS, ya que son mucho más sensibles y, por lo tanto, pueden identificar los peligros con mayor facilidad. Todos los RCD deben incluir un botón de prueba (ilustrado en amarillo en el diagrama) que permita a los usuarios asegurarse periódicamente de que el dispositivo esté funcionando correctamente.
A small amount of current - .1-.2 A - can be sufficient for an electric shock to be lethal, yet the overcurrent protection devices installed in electrical systems for lighting and outlets are generally 15 A or more. Additionally, overcurrent protection devices typically have a time delay to avoid accidentally opening (disconnecting) the circuit if there is a brief surge of current required by a surge load. If there is insufficient current flowing to activate the overcurrent protection device, this can lead to a many faults and potential hazards going unnoticed until there is an accident. An RCD is far more sensitive - can be activated by as little as 5-30 mA (.005-.03 A) of current - and will activate within 25-40 ms (.025-.04 seconds). It is recommended that an RCD is chosen with a 30 mA (.03 A) trip value.
It is recommended that a RCD be incorporated on the alternating current (AC) side of any off-grid system to improve the safety of an off-grid installation. RCDs can be found as breakers or integrated into outlets. RCDs can be put on individual circuits as a breaker or outlet or just one breaker can be used on the inverter output. RCDs on individual circuits increases system cost. One single RCD has the disadvantage of disconnecting all circuits if there is a fault, which can make it difficult to troubleshoot to determine the location of the fault.
Functioning of an RCD
An RCD works best relative to an OCPD in cases where there is a poor (high resistance) ground connection, or no equipment ground for an appliance. In the example below a refrigerator is depicted with a loose/non-existent ground. There is a fault on the ungrounded conductor (wire) inside the refrigerator, which is leaking some current to ground, but not enough to cause an overcurrent protection device to open (disconnect) the circuit or to cause the refrigerator to stop working.
- Example 1: If the system does not have an RCD then the small amount of current flowing through ground will go undetected until a lower resistance path to ground is created, which in the example is created when a person touches the refrigerator. A larger amount of current now flows through the person to ground and may trigger overcurrent protection device but not without electrocuting the person first.
Example 1 - no RCD
- Example 2: If the system has an RCD then the small amount of current flowing through ground will be quickly detected and the fault/hazard will be mitigated by opening (disconnect) (disconnecting) the circuit. The refrigerator will stop functioning, but a person will be able to safely touch it without being electrocuted.
Example 2 - with RCD
