RCD/RCMU Type B for Electrical Device Safety Protection

A Residual Current Device (RCD) is used to detect these currents and disconnect the circuit from the source automatically when the values of these residual currents exceed the predefined limits. A Residual Current Monitoring Unit (RCMU) is similar to an RCD except it does not contain the disconnection function, and can only activate an alarm. 

The IEC 60755 standard specifies three different types of RCDs, defined by their ability to sense, properly trip, and withstand different types of current:

• Type AC – sensitive to residual sinusoidal alternating current (AC). • Type A – sensitive to residual sinusoidal alternating current (AC) or pulsed direct current (DC).

• Type B – sensitive to residual AC, pulsed DC, or smooth DC currents. For the purposes of this paper, the key fact is that only Type B RCDs are able to withstand and properly function in the presence of a DC residual current component exceeding 6 mA

The residual current may be a pure alternating current (AC), a pure direct current (DC), or a current with both AC and DC components. The proper functioning of the RCD or RCMU is only ensured if the type of RCD or RCMU is matched to the type of residual current expected: AC, DC, or mixed. In some jurisdictions, RCDs are required to be installed on AC circuits in which PV inverters are connected. In a grid-tied PV system with a non-isolated inverter, it is possible for a ground fault on the PV system to cause DC residual current in the AC part of the system. Therefore, if an RCD is required on the AC circuit, its proper selection requires awareness of the properties of the inverter.

Also needed is awareness of the fact that many inverters also contain RCD or RCMU functions to protect against or warn of ground faults in the PV array, and of the limitations of such PV residual current functions.

Any electrical leak can be dangerous for your staff and production site. By using our Residual Current Devices (RCDs), you can protect both staff and equipment. Thanks to its zero-flux technology expertise, IVY Metering developed a range of highly flexible Residual Current Monitors of Type B/B+ for measuring DC and AC residual currents up to 100kHz, with digital signal output.