3 Phase Amps on PDU

I don't know much about electricty...
My question is - If this PDU (Power Distribution Unit) is rated at 20A per phase output, does that mean it can handle 60A total output on a
208V 3phase circuit?
http://www.apc.com/resource/include/techspec_index.cfm?base_sku=AP7893
Output Nominal Output Voltage 120V,208V Maximum Total Current Draw per Phase 20A Output Connections (21) NEMA 5-20R (6) NEMA L6-20R Always on Outlets 27
Input Nominal Input Voltage 208V 3PH Input Frequency 47 - 63 Hz Input Connections NEMA L21-20P Cord Length 10 feet ( 3.05 meters) Maximum Input Current per phase 16A Load Capacity 5700 VA
Another Question - Why is the input current LOWER than the output current?
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| I don't know much about electricty... | | My question is - If this PDU (Power Distribution Unit) is rated at 20A | per phase output, does that mean it can handle 60A total output on a | 208V 3phase circuit? | | http://www.apc.com/resource/include/techspec_index.cfm?base_sku=AP7893 | | Output | Nominal Output Voltage 120V,208V | Maximum Total Current Draw per Phase 20A | Output Connections (21) NEMA 5-20R | (6) NEMA L6-20R | Always on Outlets 27 | | Input | Nominal Input Voltage 208V 3PH | Input Frequency 47 - 63 Hz | Input Connections NEMA L21-20P | Cord Length 10 feet ( 3.05 meters) | Maximum Input Current per phase 16A | Load Capacity 5700 VA | | Another Question - Why is the input current LOWER than the output | current?
The difference is most likely related to the 80% loading percentage. The actual planned load on a circuit should not be more than 80% of the capacity of the circuit. The specified input maximum is the real limit you should be using. Don't put 20 amps worth of load on one phase. However, it can handle 20 amps if sometimes that happens. It should even be able to handle 25 amps or more of intermittent heavy load. Testing often applies 2 or 3 times teh current for long periods to make sure things don't self destruct under stress. But be sure you don't go over 16 amps per phase (this gives you the margin in case of some problem). So you can go up to 48 amps total if you keep it in exact balance.
The various outlets should be marked as to phase, maybe with letters or maybe with colors. The 6 round ones would be pairs of phases. Otherwise it may be hard for you to tell what your balance is.
Also, check everything you plug in for how much harmonic current will be involved. If your loads have excess harmonics, then they may not cancel out properly on the neutral, potentially overloading it to as much as 48 amps or more.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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