How to test an RCD
Updated: October 2026
The mower is still in the shed, the adaptor is on the bench, and you want to know what the test button proves. Learning how to test an RCD, for a plug-in or an in-line unit, is a short check plus a list of reasons to stop. The button shows that the device can trip. It does not measure residual current, it does not time the trip, and it does not prove the house wiring. This page is that routine. It does not rank products. The listings are on the [RCD comparison](/hub/electrical-equipment/rcd). There is no lab test.
The mower is still in the shed, the adaptor is on the bench, and you want to know what the test button proves.
The mower is still in the shed, the adaptor is on the bench, and you want to know what the test button proves. Learning how to test an RCD, for a plug-in or an in-line unit, is a short check plus a list of reasons to stop. The button shows that the device can trip. It does not measure residual current, it does not time the trip, and it does not prove the house wiring. This page is that routine. It does not rank products. The listings are on the RCD comparison. There is no lab test.
Our top picks
| Badge | Product | Form | Test | Trip current | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  EXNICEXI EXNICEXI NB-H3E-13 | Plug-in adaptor | Test, then reset | 30 mA | 9.2 | about £13.99 | View offer |
| Best value |  Masterplug Masterplug ARCDKG-ZD | Plug-in adaptor | Reset after each use | Not stated | 8.8 | about £9.94 | View offer |
 Masterplug Masterplug ILRCDNG-MP | In-line RCD | Reset after power is cut | 30 mA | 8.6 | about £12.99 | View offer |
On this page
The sequence before you plug the tool in
Do this with the appliance unplugged. Push a plug-in adaptor into a live 13 A socket. Press RESET until the indicator shows. Press TEST until it clears. If the indicator stays, do not use the adaptor. Press RESET again, then plug the appliance in. That pattern is the Masterplug ARCDKG sheet. The EXNICEXI bullets use their own words: RESET until the light is on, TEST until it goes off, then RESET. The Status SRCDORX3 names the buttons and does not describe the lamp. Do not borrow Masterplug orange for it.
The Schneider listing has no button procedure in the captured bullets. Do not invent a consumer-unit sequence and call it this module's text. Board testing belongs with a competent person. Which portable to buy is on the best RCD page, after the check, not instead of it.
When to take it out of service
Stop if TEST does nothing. Stop if RESET will not hold with nothing plugged in. Stop if the body runs hot, if a plug pin has melted, if the case is cracked, or if the indicator never shows. Do not use a faulty RCD, and do not bypass a trip. The practical line is: do not use it; remove it or label it faulty. A dim neon, which reviews mention on the Masterplug plug-in and the PRCDKB, makes the window hard to read. It is not the same as a melted pin. Melted pins on an EXNICEXI after about six weeks are a stop-using sign. If you wired the unit into a lead, take the plug out of the wall before you look at the terminals, and stop if you are no longer sure of the conductors.
A trip with an appliance plugged in
A trip during the button test, with nothing else connected, is what you wanted. A trip the moment you plug the mower or the pressure washer in is information about that appliance or its lead. Unplug it. Do not keep resetting. If the adaptor then holds with the appliance out, leave that appliance until it has been checked. If the adaptor will not reset with nothing connected, it is finished for your purposes. Remove it or label it faulty.
If the consumer unit opens, you do not open the board to investigate. A power cut is different from a fault. On a non-latching Masterplug the adaptor also opens when the supply fails, and it stays open until you reset it.
Common questions
How often should I press the button?
Before each use, if the device is portable. That is the HSE guidance and the Electrical Safety First home booklet. INDG354 adds a weekly button test for a fixed RCD, plus an instrument test at least once a year. BEAMA's six-month note is the looser general habit. It does not replace the before-use check on a plug-in you are about to take outside.
Is the test button the same as an electrician's RCD test?
No. The button only shows that the device can open. An installation test checks tripping current and time. Under BS 7671 a general non-delay RCD is verified at its rated residual current, with a maximum of 300 ms. A successful button test is not a clean bill for the circuit, and a reviewer's meter reading is not that verification.
What if the indicator stays on when I press TEST?
Do not use the adaptor. The Masterplug sheets say that if the indicator remains, the unit is not to be used. Remove it or label it faulty, and do not bypass it with an ordinary plug. The same stop applies if the indicator never moves. A dim lamp that still changes is a poor window. A lamp that never changes is a failed check.
What if it will not reset after a power cut?
On a non-latching Masterplug, that is the design. The ARCDKG sheet says the unit trips whenever the supply is interrupted, including when the appliance is switched off. Press RESET, then run the test before you use the tool. If RESET will not hold with the appliance unplugged, stop. The Status listing and the Schneider do not state this behaviour, so do not explain a dead reset on those as non-latching.
Should I keep using it if the body is hot or a pin has melted?
No. Take it out of service. Heat that ends in a melted pin, a cracked case, or a unit that will not stay reset matches the review pattern here, including melted pins on an EXNICEXI after about six weeks. Do not tape the button. A shock can still be fatal when an RCD is working. A damaged one should not be in the socket.
Related pages
Sources
Public UK sources are listed below. Shelf prices and star lines are the amazon.co.uk figures checked on 19 October 2026.
- HSE: work using electrically powered equipment (retrieved 19 October 2026)
- HSE: electrical systems on construction sites (retrieved 19 October 2026)
- IET Wiring Matters: 30 mA socket-outlet mythbuster (retrieved 19 October 2026)
- IET Wiring Matters: RCD testing under Amendment 2 (retrieved 19 October 2026)
- IET Wiring Matters: which RCD type (retrieved 19 October 2026)
- Electrical Safety First: garden (retrieved 19 October 2026)
- GOV.UK: building work, replacements and repairs (retrieved 19 October 2026)
- BEAMA guide to the selection and application of RCDs (August 2022) (retrieved 19 October 2026)