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Power Cord and Outlet Locking
Power cord and outlet locking mechanisms secure the
physical connection and ensure the power cords are not
accidently pulled out of the outlet, causing an inadvertent
load drop. (Figure 3) Globally, the most common standard
for outlets used in rack PDUs is IEC320 C13 and C19. IEC
receptacles are internationally acceptable and handle output
voltages up to 250V.
Figure 3. Locking outlets and locking power cords
prevent accidental unplugging of IT devices.
Functionality
Intelligent rack PDUs should be able to provide proactive
notication of impending issues before they occur. Warning
and critical threshold settings for the current ensure that the
rack PDUs do not experience overload conditions that
could otherwise trip the breaker and the connected loads.
While setting the current conguration, care should be taken
that in a typical 2N scenario at the rack level, the thresholds
for the branches are set at less than 50 percent of the overall
rack PDU rating.
Software Electronic OCP
Paired with proactive monitoring, this feature will turn off
and lock down all unused outlets on a branch circuit that has
exceeded current established thresholds. It basically prevents
someone from plugging new equipment into an unused outlet
and causing a circuit overload.
Additional parameters that an intelligent rack PDU needs to
monitor to ensure high availability:
1. Phase currents, along with a notication of
unbalanced loads.
2. Temperature within the rack, through integrated sensors,
along with the ability to congure auto turn-off outlets
when temperatures exceed critical thresholds.
3. Ability to monitor circuit breaker status. (This is
typically found in rack PDUs with metering or switching
capabilities down to the outlet level. For rack PDUs with
metering capabilities only at the branch circuit level, low
critical threshold could be monitored as a proxy for circuit
breaker status.)
All notications should be capable of being received in a
familiar format, such as SMS, SNMP traps or e-mail. Power
distribution units should be capable of integration with a
centralized management software, which will enable them to
be easily managed.
Fault Tolerance
Intelligent rack PDUs should be designed such that a loss of a
single phase will not lead to dropped power on all the
unaffected phases. Also, regardless of the advanced features
offered by an intelligent rack PDU, it needs to continue to
provide basic power distribution in the event of a compromise
of the intelligence capabilities. Fault tolerance due to a loss of
the one of the main intelligence capabilities (i.e. switching,
metering and external connectivity) is based on the design of
these capabilities.
Metering
Current sensing within electrical circuits can be provided
through the use of shunts, current sensors or Hall Effect
sensors. Because shunts sit in the path of high voltage power,
an issue with the shunt itself often leads to disruption of
power within the primary circuit. On the other hand, current
transformers and Hall Effect sensors are coils that are
isolated from the primary high voltage circuit. Therefore, a
disruption of power to these sensors themselves has minimal
impact on the power owing through the primary path.
Current transformers have a further advantage over Hall
Effect sensors in that they provide higher accuracy.
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