How quickly should an RCD not exceeding 30mA x5 test (150mA) operate?

The correct answer is based on the specified time frame within which a Residual Current Device (RCD) should operate when subjected to a test. For RCDs rated at 30mA, the standard requires that they trip within a certain period to ensure protection against electric shock and fire hazards.

For an RCD with a rating of 30mA subjected to a test current that is five times its rated current— equating to 150mA—the operating time must not exceed 40 milliseconds. This ensures that in the case of a fault condition, the device will disconnect the supply quickly enough to minimize the risk of serious injury or damage. The 40ms threshold is in alignment with safety standards that dictate the maximum allowable tripping time for effective protection.

In summary, the expected performance of an RCD operating at 150mA is crucial for its effectiveness in protecting users and property from electrical faults, thereby making 40 milliseconds the appropriate and correct answer for this scenario.