Appendices 79
Appendix C: Circuit Breakers
The PM IPDU circuit breakers are designed to shut the power off to some or all of the PM IPDU
outlets in case the rated current is exceeded. The circuit breaker mechanism for each PM IPDU
model is explained the in the following sections.

PM IPDU Units with One Circuit Breaker

Only one circuit breaker is used for the following units:
• PM8-15A IPDU
• PM8-20A IPDU
• PM8-L20 IPDU
• PM10-15A IPDU
• PM10-20A IPDU
• PM10-L20 IPDU
• PM20-20A IPDU
• PM20-L20 IPDU
• PM20i-16A IPDU
• PM20i-20A IPDU
In the event of a current overload in any of these units, the entire unit shuts down causing all outlets
to disconnect.

PM8i IPDU and PM10i IPDU

The PM8i IPDU and some versions of the PM10i IPDU (10, 15, 16, and 20 amps) have two circuit
breakers each. Both circuit breakers are designed to protect different phases of the same circuit
inside the unit. If either one of the two circuit breakers trips, the entire unit will shut down.

PM10-L30A IPDU

The PM10-L30A IPDU has two 15-amp circuit breakers. The first circuit breaker controls outlets 1
through 5 and the power supply to the logic board; the second circuit breaker controls outlets 6
through 10. If the total current flow to outlets 6 through 10 exceeds 15 amps due to equipment
connected to these outlets, then the second circuit breaker will trip causing outlets 6 through 10 to
shut down. This does not affect outlets 1 through 5, which are controlled by the first circuit breaker.
If, however, current overload causes the first circuit breaker to trip, then the entire power unit shuts
down because the power supply is also tied to the first circuit breaker.
Refer to Table C.1, “Circuit Breaker Trip Time,” on page 83 to determine the time it takes for the
circuit breaker to trip based on the amount of current overload.