From the test results as a part of the study referenced here, common ICT power supplies do not align completely with the ITIC/CBEMA curves. In fact, there is significant variability from one power supply to the next.
Within a server power supply, there is a signal created which is named “Power OK.” This is a discrete, go/nogo indicator to the serer electronics of proper input power availability. The performance of the Power OK signal, according to our testing, is quite suspect. Sometimes it has no reflection at all of what is happening with the DC supply voltage. It sometimes will fall in advance of the supply failure, sometimes afterwards, and sometimes not at all, depending on the specific power supply unit.
The bottom line is that it appears that resilience to a 10mS input power outage is the best we can count on. Beyond that, it’s a case by case situation. The problem is knowing the case.
The evidence suggests that ride-through times of server power supplies has been reduced since establishment of the ITIC/CBEMA curve. Consequently, the curve cannot be counted on to reflect power supply performance to power quality degradations in contemporary ICT equipment.
By Bob Landstrom
(This is Part-6 of a 9-part series on a modern assessment of the ITIC/CBEMA curves)