What is a Ramp Test?

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Question:

Whilst looking at different specifications of test equipment, I’ve come across the phrase ‘ramp test’. I know this has something to do with testing RCD’s, but what is a ramp test?

Answer:

An RCD ramp test is a test used to determine what fault current a residual current device will actually operate, or trip, at.

A tester that offers this facility will ‘ramp up’ current through an RCD in stages until the RCD finally trips. For instance, a healthy 30mA RCD should trip between 27mA and 30mA with all electrical appliances disconnected. If by conducting a ramp test your tester trips the RCD outside of these thresholds, you could have a faulty device that may be prone to nuisance tripping.

Likewise, you could conduct a ramp test if you suspect a particular electrical appliance to be faulty. For example a 30mA RCD may trip at 12mA by conducting a ramp test with the suspect appliance connected and then at 27mA with the appliance removed. You will know that the appliance is leaking approximately 15mA.