PDU tripping unexpectedly...

QN: do I have a bad PDU?


3 servers, each connecting to 2 PDU's via dual power supplies. Each PDU was showing 6.3 A load. (15 A max.)

When moving all 3 outlets off PDU so it could be physically moved, PDU B tripped its overload breaker.

The nameplate load of the 3 servers is > 15A, but the combination of 2 x 6.3 (measured Amps) is not.

So, it seems either: - PDU B is bad

- the measurements of 6.3 A on each circuit is incorrect

- there is a power draw spike when servers switch from 2 power supplies to 1.

Does anyone know if the latter case is true? Or have other theories? Thanks

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with a dual power supply computer, when both supplies are running, they usually are designed to share the load equally. So when you pull the plug on power supply A, now power supply B is supporting the entire load. So basically you doubled the load on the PDU when you shut off the first one. ( handwaving power factor, derating and so on) This is also an indication of a deeper problem in your data center. If one of your PDUs goes down the other one is going to go down from the overload. So your much more expensive dual power supply computers are not actually protecting you from a PDU failure. I suggest you get an experienced data center infrastructure person to come in and do an assessment on the place, to identify other not so obvious problems that are lurking for murphy to dump on you.


Reply to
Dale Farmer

Well, I know I doubled the load, but 2 x the shown 6.3 Amps per circuit should still leave one circuit running at 12.6 A, which is less than their limit of 15A. So why the trip?

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