What is an RCD trip test?

Glossary · Testing, inspection and certificates

How an RCD trip test works

A residual current device, or RCD, cuts the supply when it detects current leaking to earth, for example through a person or a damaged cable. A trip test checks that it really does switch off, and fast enough. There are two kinds of test, and they are done by different people.

The electrician’s test. An electrician connects a test instrument and applies an alternating current at the RCD’s rated residual operating current. The IET says that for general non-delay RCDs, the maximum operating time must not exceed 300 milliseconds. For an S type time-delayed RCD, the operating time must be between 130 and 500 milliseconds.^{[1]Institution of Engineering and Technology (IET), Changes to RCD testing in BS 7671:2018+A2:2022 (Wiring Matters, July 2022)} The IET also says RCD testing is needed where RCDs give fault protection or additional protection.^{[4]Institution of Engineering and Technology (IET), Minimizing unnecessary live testing for initial verification (Wiring Matters, May 2025)} NICEIC lists it as one of the circuit tests in an EICR.^{[5]NICEIC, Electrical Installation Condition Reports (EICRs)}

The householder’s test. Most RCDs have a button marked T or Test. The guidance printed on the BS 7671 Electrical Installation Certificate says an RCD should be tested every six months by pressing it. The device should switch off the supply, and you then switch it on to restore the supply. If it does not switch off when the button is pressed, seek expert advice.^{[2]Institution of Engineering and Technology (IET), BS 7671:2018+A4:2026 model forms for certification and reporting (Electrical Installation Certificate)} Electrical Safety First gives the same advice: use the test button regularly, and get a registered electrician to investigate if it does not work.^{[3]Electrical Safety First, FAQ for Electrical Safety - Your Questions Answered}

Two tests compared

The button check is the only part a householder should do. Our page on resetting a tripped consumer unit covers what to do if a device trips on its own.

Example

Sam lives in a flat in Meanwood. Every six months he presses the Test button on the RCD in his consumer unit. The switch drops, the lights go off, and he switches it back on. At his EICR, the electrician then tests each RCD with an instrument and records the trip time. The report shows each device tripped within the limit for its type.^{[1]Institution of Engineering and Technology (IET), Changes to RCD testing in BS 7671:2018+A2:2022 (Wiring Matters, July 2022)} If Sam’s RCD had stayed on when he pressed the button, he would have called a registered electrician, as the form guidance says.^{[2]Institution of Engineering and Technology (IET), BS 7671:2018+A4:2026 model forms for certification and reporting (Electrical Installation Certificate)}

What people get wrong

Many people think the test button and the electrician’s test are the same thing. They are not. The button checks the device switches off. The electrician’s test measures how quickly it does so at the rated current. The six-monthly button check does not replace the inspection.

The IET’s 2022 article on Amendment 2 also says that the older requirement for a second test at five times the rated current was removed.^{[1]Institution of Engineering and Technology (IET), Changes to RCD testing in BS 7671:2018+A2:2022 (Wiring Matters, July 2022)} Your electrician applies the edition of BS 7671 in force when they test.

Persistent tripping with nothing wrong is a separate fault. See our page on why your RCD keeps tripping, and the differences between devices in RCD vs RCBO.

The bottom line

An RCD trip test proves that your residual current device does its job. The electrician measures it with an instrument and a 300 millisecond limit applies to a general RCD. You press the Test button every six months and switch the supply back on. If it does not switch off, call a registered electrician. Our electrical safety inspections page explains how we test.