Why does my RCD keep tripping in Cardiff?
RCD keeps tripping in Cardiff? Common causes, what you can check safely and same-day diagnosis from a NICEIC engineer.
Local demand for fault diagnostics follows the housing stock here, which is largely Victorian and Edwardian terraces across Cathays and Roath. An RCD that keeps tripping is the most common emergency callout we attend in Cardiff — and it's almost always one of three things: a faulty appliance, accumulated dampness, or a cable fault. Most enquiries about this start with a symptom and end with insulation resistance test pinpoints the circuit. We would rather set that expectation now than on the day. Two properties on the same street can differ on this entirely. The practical question for a Cardiff property is not what usually happens, but what this installation actually shows when it is tested. Neither of us benefits from finding that out halfway through. For Victorian and Edwardian terraces across Cathays and Roath in particular, fault diagnostics throws up a fairly predictable set of findings.
- One of the usual points: same-day diagnosis if you can't isolate it
- Faulty appliance (most common cause) This is the part people ask about most.
- Poor previous workmanship shows up as faulty appliance (most common cause) more often than material failure does.
- The pattern we see near the A470 and A48 is damp in outdoor/bathroom circuits.
- Cable damage behind plaster. If it is not this, testing narrows it down quickly.
What's different about Cardiff
One of the usual points: many older Cardiff properties still run on rewireable BS 3036 fuse boxes that no longer meet 18th Edition requirements — older RCDs lose sensitivity over time and trip on tiny earth leakage that a new device would tolerate.
If the trip is on a shower or outdoor circuit during rain, dampness is the likely culprit and the fix is usually IP-rated kit, not a board change. This is the part people ask about most.
A recurring one across CF10–CF24: failed RCD itself (rare but happens).
Same-day diagnosis if you can't isolate it, which is why the whole circuit gets tested and not just the visible part.
How we'd do it
- 1IsolateUnplug appliances one by one to find the culprit, and the outcome decides the next step rather than a sales script.
- 2TestInsulation resistance test pinpoints the circuit. This is the part people ask about most.
- 3FixInsulation resistance test pinpoints the circuit — the same process whether the property is in Cardiff or Penarth.
- 4CallTypically for Victorian and Edwardian terraces across Cathays and Roath: if you can't isolate it, phone for diagnosis.
Common questions
Is it safe to keep resetting it?
Once or twice is fine. If it trips repeatedly, stop and call.
What is the most common outcome?
A defined, limited piece of work. Cable damage behind plaster usually resolves without replacing the whole installation.
Do you handle larger planned projects?
Yes, phased across a programme so the Cardiff site stays usable while work proceeds.
Why does testing take so long?
Because each circuit is measured individually. Same-day diagnosis if you can't isolate it would be missed by a walk-round inspection.
Do you cover Cardiff for fault diagnostics?
Around CF10–CF24: yes — Cardiff and the surrounding CF10–CF24 postcodes are part of our regular working area, including Penarth and Caerphilly, and Cardiff Council notification is handled by us where the work requires it.
How soon can this be booked?
Availability varies week to week. Cardiff is on our regular round, so it is usually a matter of days rather than weeks.
If a survey is the sensible first step, we will say so and price it separately so you are not paying twice. We cover Cardiff and the CF10–CF24 postcodes, including Caerphilly, for fault diagnostics. Describe what the property is doing and when it started. Most enquiries are answered properly within the day. We cover Cardiff and the CF10–CF24 postcodes, including Pontypridd, for fault diagnostics.