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Old 06-24-2008, 05:29 PM   #1
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Power in a server room


We have 20 amp circuits in our Class A Class 1 whatever AT&T data center. My company doesn't want to put more than 13 amps on a 20 amp circuit because they are worried about surges on start up or a reboot tripping the breaker and causing the whole half rack to go out (2 power strip per rack I think). From what I've read here 16 amps running 24/7 should be fine. We have APC power strips with ammeters built in. Any thoughts on this?

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Old 06-24-2008, 10:53 PM   #2
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Power in a server room


It depends on what is measuring the current. Switching type power supplies (like the ones in computers) have distorted waveforms, and current cannot be read accurately with meters that are not 'true RMS'.

I wouldn't be comfortable loading a circuit breaker to 80% (16 amps) of its rating, simply because, due to manufacturing tolerances, a few breakers here and there might trip at this level. At 65% (13 amps), you'd be completely safe. If any of these are multi-wire circuits, and it's a 3 phase panel, the current in the neutral can be (usually is) higher than in the hots. This is due to harmonics generated by non-linear loads, like switching type power supplies.

Rob

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