What are the technologies used in RCD?


13 July 2023

Voltage Independent Technology
Residual current devices using Voltage Independent Technology can continue to operate in the event of a complete voltage loss or neutral break.

The residual current device consists of:
  • high magnetic performance core (ex: nanocrystalline)
  • a high-sensitivity relay
  • an electronic interface analyzing the signal.
  • The toroid provides information on the leakage current and the power required to trip the device.
  • The electronic circuit and the relay are not connected to the electrical network. Power is provided only by the leakage current.
  • Even if there is an accidental break of the neutral conductor or a voltage drop, the entire electromechanical system will continue to operate, allowing the residual current device to trip.

Voltage Dependent Technology (with and without FE)
A voltage source is required to operate this technology.
For Schneider Electric residual current devices, earth fault protection is provided in the event of a voltage drops down to 50 V.

In the case of VDT technology ("Voltage Dependent Technology"), the toroid only provides information about the leakage current.
The power required for tripping is supplied by the electrical network.

"Voltage Dependent Technology" RCDs supplied via the FE (Functional Earth)
In the event of loss of supply (required to address the fault and trip), there are two categories of behavior:
  • Category 1: the RCD does not open and continuity of service is optimum, because the load is powered on when the voltage is restored, but the RCD is unable to operate if the loss of power supply is the result of a neutral break. The presence of line voltage is a hazard because the RCD is no longer able to perform its protection function in the event of contact with the line potential
  • Category 2: the RCD opens if there is loss of power supply (including in the event of neutral break). After the voltage is restored, the RCD must be reclosed to power on the load again.
To improve the level of protection provided by category 1 RCD, in the event of neutral breaking, the product is supplied by redundancy via the FE (line to FE supply instead of line to neutral), allowing it to continue to perform its protection function.
This configuration allows the behavior of VDT RCDs to be compared with that of VIT RCDs.
  • conformity with the standards is confirmed by a national conformity mark on the product. The mark is assigned by a third-party organization independent of Schneider Electric. This involves regular sampling at the production site to ensure continued conformity with the standards in question.
According to the standard requirements, all electrical equipment protected by VD with FE RCDs must be earthed to ensure maximum earthing resistance as follows:
  • Ue = 110 V: 50 ohm,
  • Ue = 230/240 V: 100 ohm.

Reference document - CA908066E