RCD Trip Time and IEC 61008 Test Requirements
What is the maximum trip time for an RCD? IEC 61008-1 sets maximum break times for RCCBs at three test currents — IΔn, 2×IΔn and 5×IΔn — with the limit tightening as the fault current multiple increases, plus a separate, slower band for S-type selective devices. Miss that budget and touch voltage stays applied longer than the body can safely tolerate, or an upstream device opens before the intended downstream circuit does. This article covers the IEC 61008-1 time-current table, why testing uses three multiples of IΔn instead of one, the gap between general and S-type break times, what a commissioning tester actually measures versus the front test button, and how selectivity delays sit inside the same numbers.
How IEC 61008-1 Defines Maximum Break Time
Break time (ta) runs from the instant residual current reaches the test value to the instant the contacts fully separate. IEC 61008-1 does not give one number — it defines a curve, checked at three points: 1×IΔn, 2×IΔn and 5×IΔn. At 1×IΔn the device is proving it trips at all, close to its rated threshold, so the standard allows the most time. At 5×IΔn the fault is unambiguous and severe, so the allowed time drops hard. A 30 mA general-type RCCB must clear a fault at 1×IΔn within 300 ms; at 5×IΔn (150 mA) that window shrinks to 40 ms.
Formula: Maximum Break Time — Source: IEC 61008-1
ta(n) ≤ tmax at n × IΔn
| Symbol | Description | Unit |
|---|---|---|
| IΔn | Rated residual operating current | mA or A |
| n | Test current multiplier (1, 2 or 5) | — |
| ta | Actual break time measured at n × IΔn | ms |
General (Instantaneous) vs S-Type Break Times
General-type RCCBs are built to open as fast as the mechanism allows. S-type (selective) RCCBs are built the opposite way: they carry a deliberate minimum non-actuating time so a downstream general-type device gets first chance to clear the fault. Both are checked against IEC 61008-1, but the S-type table has a floor as well as a ceiling.
| Test Current | General (Instantaneous) | S-Type (Selective) |
|---|---|---|
| 1 × IΔn | ≤ 300 ms | 130–500 ms |
| 2 × IΔn | ≤ 150 ms | 60–200 ms |
| 5 × IΔn | ≤ 40 ms | 50–150 ms |
Read the S-type row again: the minimum at 1×IΔn is 130 ms, not zero. That gap is intentional — it is the coordination margin that lets a board built for RCD selectivity in detail hold the upstream device open while the branch circuit trips first. Swap an S-type for a general-type at the head of a board with sub-distribution, and that margin disappears; both devices race, and the one that wins is not guaranteed to be the branch circuit.
Test Currents: Why IΔn, 2×IΔn and 5×IΔn, Not Just One
A single test point would hide a device that trips fine at rated current but drags at higher fault levels, or one that is oversensitive at low levels but sluggish above it. Testing at three multiples forces the whole curve into spec, not just one point on it. It also mirrors the range of real leakage a device sees: a 30 mA RCD selected for RCD sensitivity ratings for personal protection has to behave correctly whether the fault current is barely above threshold or five times over it.
Why the 300 ms Limit Matters for Personal Protection
Ventricular fibrillation risk in a person rises with both the magnitude and duration of current through the body. A 30 mA device that clears within 300 ms keeps the let-through energy low enough to sit inside internationally recognized safe zones for a healthy adult, which is the reason 30 mA is written into most wiring codes as the standard human-protection value rather than 100 mA or 300 mA. Fire-protection sensitivities (100/300/500 mA) use the same break-time logic but are sized to clear leakage before it can ignite insulation or dust, not to stay under a shock threshold.
What we see in the field: panel builders sometimes treat the test-button click as proof the timing is fine. It isn't. The button injects an artificial imbalance through a resistor built into the device — it proves the trip mechanism and coil are alive, nothing about actual break time at IΔn, 2×IΔn or 5×IΔn.
Commissioning: What an RCD Tester Actually Measures
A proper commissioning test uses a dedicated RCD tester, not the built-in button. Two measurements matter. First, trip time at IΔn: the instrument injects a current equal to the rated sensitivity and times the break, comparing it against the IEC 61008-1 limit for that device's class. Second, a ramp test: current rises gradually from zero until the device trips, recording the actual current at which it operates. The ramp result should land close to IΔn — a device that trips at 60% of rated current is oversensitive and will nuisance-trip in service; one that trips at 150% of rated current is undersensitive and may not protect as intended. See the full procedure in our instrument testing procedure guide.
Selectivity: Building Time Delays Into the Same Table
Discrimination between two RCDs in series depends on both current ratio and time delay, and the break-time table above is where that delay actually lives. The rule of thumb: the upstream device's IΔn should be at least twice the downstream device's IΔn, and the upstream device should be an S-type so its minimum non-actuating time (130 ms at 1×IΔn) exceeds the downstream general-type's maximum break time (300 ms is still slower here, which is why the ratio condition also has to hold — at higher multiples the S-type's 60–200 ms band clears the downstream general-type's 150 ms ceiling with margin). Get the ratio wrong, and even a correctly time-delayed upstream device can trip alongside the branch circuit instead of after it.
This is where residual current devices get specified as a coordinated set rather than picked one board at a time — mixing brands or skipping the ratio check on a retrofit is a common way selectivity quietly breaks.
Where Trip-Time Requirements Fit Against RCCB, RCBO and MCB Choices
Trip-time limits apply the same way whether the residual-current function sits in a standalone RCCB or inside an RCBO that also carries overcurrent protection — the IEC 61008-1 timing curve governs the earth-leakage element in both. What changes is the overcurrent path: an RCCB has none and must be backed by an MCB, while an RCBO integrates both in one module. For the terminology split between these device families, see our guide on RCBO vs RCCB terminology. Procurement teams sourcing RCBOs for a panel with mixed final circuits still need to check the trip-time class (general or S-type) against the board's selectivity plan, not just the sensitivity and pole count.
For the broader technical background behind all of this — construction, sensitivity classes, earthing systems and selection — see the full RCD protection guide.
Frequently Asked Questions
What is the maximum trip time for a 30 mA RCD?
Under IEC 61008-1, a general-type 30 mA RCCB must clear a fault within 300 ms at 1×IΔn (30 mA), within 150 ms at 2×IΔn (60 mA), and within 40 ms at 5×IΔn (150 mA). S-type selective devices are allowed longer, with a defined minimum as well as a maximum at each point.
What is the difference between general and S-type break times?
General-type devices only have a maximum time limit and are built to trip as fast as possible. S-type devices have both a minimum and a maximum, because the minimum delay is what lets a downstream general-type device clear the fault first on a selective board.
Why is an RCD tested at 2×IΔn and 5×IΔn, not just IΔn?
A single test point cannot confirm behavior across the full range of fault currents a device may see in service. Testing at three multiples verifies the device meets its time limit near threshold and at higher, more severe fault levels, not just at one value.
Does pressing the test button confirm the trip time?
No. The test button injects an artificial imbalance through an internal resistor to confirm the trip mechanism and coil function. It does not measure break time, verify the trip threshold, or exercise the device at IΔn, 2×IΔn or 5×IΔn as required by IEC 61008-1.
What happens if an RCD trips slower than IEC 61008-1 allows?
A device that exceeds its break-time limit no longer provides the protection level its rating implies — for a 30 mA personal-protection device that can mean unsafe shock duration, and for a selective board it can mean the wrong device opens first. A slow result on a commissioning test means the device should be replaced, not returned to service.
Conclusion
IEC 61008-1's trip-time requirement is a table, not a single number: 300 ms, 150 ms and 40 ms for general-type devices at 1×, 2× and 5×IΔn, with a slower and floored band for S-type devices that exists specifically to make selectivity possible. The test button proves the device can trip; only an instrument test at those three multiples, plus a ramp test for actual trip current, proves it trips within spec. On any board where an upstream S-type has to hold while a downstream general-type clears first, that timing table is the selectivity plan, not a background compliance detail.
