# Tripping a circuit breaker when using a half wave rectifier

How does a half wave rectifier or phase control dimmer affect the triggering of a circuit breaker? For example, if a 20A resistive load was on a 15A breaker with a half wave rectifier. Now average RMS current is only 10A even though peak RMS is still 20A.

• You worked it out yourself ….the breaker is rated at an RMS current so it's the RMS load current that will mainly cause the trip. However many breakers have a mag element which will trigger at high peak currents and even the thermal element will trip at high peak currents. Commented May 20, 2019 at 0:15
• No. a 20A (full wave)resistive load run at 50% duty cycle is 14.1A RMS Commented May 20, 2019 at 1:51
• average RMS current what does that even mean? Commented May 20, 2019 at 2:51
• A link to the breaker's datasheet would be a help as we could check the trip times. Commented May 20, 2019 at 6:26
• @Jasen I did not know that the RMS of a 50% duty cycle sine wave was not RMS(100%)/2...though I see it now after playing around on Wolfram. Since I thought it was a simple relationship I was doing [RMS(1st half)+RMS(2nd half)]/2 which is were I got "average RMS current" from. Commented May 22, 2019 at 23:12