Nuisance Tripping Problems
Nuisance tripping occurs when an RCD trips when the residual current flowing in the circuit is less than its rated residual operating current. This may be caused a current surge or voltage surge or possibly noise on the installation.
The most common reason for nuisance tripping is a transient current to ground which is above the threshold of the RCD and subsequently causes the RCD to trip. However the transient may be only of a few milliseconds in duration but the combination of the magnitude and duration causes the RCD to trip and remove power.
At Western Automation we build our RCDs to cope with the highest possible level of immunity based on the specific needs and requirements of our customers. For example, we have designed RCDs that can withstand and completely ignore a surge current of 3000 amps and higher for a short period of time.
Inrush currents are another common event that can cause nuisance tripping. When electrical equipment is first turned on, the resultant inrush current flow could exceed the steady current value. Prior to power up, equipment tends to be either cold or the resistance or impedance may be very low. For the given voltage, the current would be at its maximum at power up, and as the equipment warms up the current will taper off. An inrush current of 100 amps for example could cause the RCD to trip because some of that inrush current may be seen as a differential current by the RCD.
During our R&D phase we perform multiple core balance tests to determine the level of balanced current that can be applied to a load with the conductors passing through the RCD core. Using a load current of 40 amps for example, we will pass a current in excessive of 240 amps to load momentarily to ensure that the RCD does not trip.
We have developed specific RCDs that go beyond the normal product standards. Known as A+, F, B and B+ Type RCDs, these superior solutions can withstand surge currents in excessive of 3000 amps without tripping. They will withstand an inrush current for 10 milliseconds and only begin monitoring the inrush current after 10 milliseconds. This range of RCDs provide excellent resilience against nuisance tripping.
There are many installations were nuisance tripping is totally unacceptable and this range of RCDs is invaluable to such applications. During our detailed design and development process, we place much emphasis on testing to ensure that our range of RCDs can clearly make the distinction between an actual fault and a non-fault condition. We work closely with our customers to gather vital information regarding the intended application for a product to ensure the correct level of immunity is provided by the RCD.