Residual Current Devices (RCD’s) are more and more frequent in the increasingly safety conscious electrical installation industry. Designed to trip within thousandths of a second under fault currents as small as 5mA, RCD’s are installed to prevent the risk of electrocution and fire in in the event of an electrical fault.
The key component within an RCD is a current transformer, upon which the line and neutral conductors are wound in opposite directions. If no earth fault current is flowing, the magnetomotive force generated by the line and neutral current windings are both equal; there is no resultant flux in the transformer and the detecting winding within the transformer does not generate any current.
When a fault current flows there is a difference between the line and neutral currents which will generate a resultant flux in the transformer, thus inducting a current in the detecting winding, allowing the RCD to operate.
Most RCD’s feature a mechanical trip button which a user is advised to press every quarter of a year. Although this will prove the RCD is working mechanically, a contractor needs to know how quickly the RCD operates under different fault conditions to meet the trip times specified in the BS7671 Wiring Regulations.
We stock a wide range of residual current device testers including Megger, Kewtech, Socket and See and Martindale. Some RCD testers or analysers offer the ability to conduct an automatic RCD test which enables the engineer to perform all six RCD tests at once. Simply leave the tester connected to the circuit under test and reset the RCD after each test in one trip, rather than resetting and testing in sequence.