RCD trip-time limits (BS 7671 test times)

Name: RCD trip-time limits (BS 7671 test times)
Author: SparkCerts

RCD trip-time limits (BS 7671)

The maximum disconnection times an RCD must meet on test, with the actual test currents for the device rating you pick. Compare them with the times on your tester.

Quick answer. A 30 mA general (non-delayed) RCD must operate within 300 ms at its rated current and within 40 ms at five times rated current (150 mA). The 40 ms figure applies where it provides additional protection.

Built by SparkCerts, certificate and job software for UK electricians. Figures follow BS 7671 and the IET On-Site Guide. Updated June 2026.

RCD type

Rated residual current IΔn

Maximum operating times from BS 7671 Table 3A (BS EN 61008 / 61009). A 30 mA RCD used for additional protection must operate within 40 ms at 5 IΔn.

What the RCD test is checking

An RCD has to disconnect fast enough to protect against electric shock. BS 7671 sets maximum operating times an RCD must meet at multiples of its rated residual current (IΔn), and your tester applies those multiples and times the trip. The figures above are the limits to compare against.

The three tests

x0.5 IΔn: the RCD must not trip. Half the rated current should not be enough to operate it.
x1 IΔn: a general (non-delayed) RCD must trip within 300 ms. An S-type is deliberately delayed (130 to 500 ms) so it can grade with RCDs downstream.
x5 IΔn: the fast test. A general RCD must trip within 40 ms.

30 mA and additional protection

A 30 mA RCD providing additional protection (sockets, cables in walls, most domestic circuits) has to operate within 40 ms at five times its rating, which is 150 mA. That 40 ms figure is the one that matters most on a domestic test sheet. Record the worst-case time, and pair this with the max Zs checker for the disconnection side of fault protection.

FAQs

What is the maximum trip time for a 30mA RCD?

A 30 mA general (non-delayed) RCD must operate within 300 ms at its rated current and within 40 ms at five times rated current (150 mA). The 40 ms figure applies where it provides additional protection.

What should an RCD do at half its rated current?

It must not trip. At 0.5 times the rated residual current (15 mA for a 30 mA device) the RCD should hold, which confirms it is not over-sensitive.

What are the trip times for an S-type RCD?

An S-type (selective, time-delayed) RCD must trip between 130 and 500 ms at rated current and between 50 and 150 ms at five times rated current. The delay lets it grade with non-delayed RCDs downstream.