How accurate is the current monitor on an APC Rack PDU (AP7XXX or AP8XXX)?

Issue

How accurate is the current monitor on my APC Rack Power Distribution Unit (PDU)?



Product Line

• Rack Power Distribution
  • Models beginning with AP7XXX
  • Models beginning with AP8XXX

Envrionment
 

• All serial numbers
• All firmware versions (unless otherwise noted)

Cause

This article outlines the accuracy for each of our Rack PDU generations. Sometimes this information is regard for general knowledge or to help explain why certain values are being observed.



Resolution

Refer to the information below for both AP7XXX PDU models and AP8XXX PDU models.


APC's 1G Rack PDUs (AP7XXX) are tested at a current load of 17.5 amps at Crest Factor of 3.0 to Outlet #1 (phase L1).

Below are the accuracy specifications in regards to the load: 

Range	Accuracy
0-1A	+/- 1.0A
1-10A	+/- 0.5A
>10A	+/-5% A

Also, as of Rack PDU (rpdu) firmware >3.3.1, attached loads < 1 amp will always display as 0 amps on the PDU's LCD and network management card, regardless of the load. Lastly, readings via the Rack PDU's network management card will give measurements in decimal format. ie. 1.6 amps as opposed to 2 as seen on the Rack PDU's LCD.


 

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APC's 2G Rack PDUs (AP8XXX) have an accuracy of +/- 3% of reading, +/- 1 least significant digit across the entire power and temperature range.  Note: Accuracy is not defined below 0.5A.


rpdu2g firmware v5.1.1 and below:

Phase and bank current measurements less than 0.5 amps, and corresponding power measurements, are rounded down to zero. 

 

For AP84XX and AP86XX SKUs with individual outlet metering, outlet current measurements less than 0.5 amps and outlet power measurements less than 50 watts will be rounded down to zero.


rpdu2g firmware v5.1.2, v5.1.6:

• Phase/Bank/Outlet Current - squelched to 0A under 0.5A.
• Device/Phase/Outlet Power - squelched to 0 watts if corresponding current is squelched.
• Outlet Energy - Will NOT be accumulated if corresponding outlet power/current is squelched.
• Device Energy - Will always accumulate, since the unit does consume a very small amount of energy within the internal circuitry.
   

rpdu2g firmware v6.0.9 and above:

• Outlet Current - squelched to 0A under 0.3A. Note: Accuracy is not defined below 0.5A.
• Phase/Bank Current - squelched to 0A under 0.5A.
• Device/Phase/Outlet Power - squelched to 0 watts if corresponding current is squelched.
• Outlet Energy - Will NOT be accumulated if corresponding outlet power/current is squelched.
• Device Energy - Will always accumulate, since the unit does consume a very small amount of energy within the internal circuitry.

 

Functional Specifications - Metering
Input Metering Range	0.5 to Rated Input Current
Outlet Metering Range	0.3 to 16.0A
Allowable Crest Factor	1.75
Accuracy (Phase Current)	+/- (3% + 1 digit)
Accuracy (Phase Voltage)	+/- (3% + 1 digit)
Accuracy (Phase Power)	+/- (3% + 1 digit)
Accuracy (Phase Energy)	+/- (3% + 1 digit)
Accuracy (Outlet Current)	+/- (3% + .1Amp)
Accuracy (Outlet Voltage)	+/- (3% + .1Volt)
Accuracy (Outlet Power)	+/- (A reading * V error) + (V reading * A error)
Accuracy (Outlet Energy)	+/- (A reading * V error) + (V reading * A error)*hours
Accuracy (Bank Current)	+/- (3% + 1 digit)

Note: It is possible that a higher level measurement will show a load (such as bank or device), even when a lower level measurement is showing zero. (For instance, the phase current could show 0.8A, even though the bank currents are squelched to zero.)


How to verify your firmware PDU NMC firmware version: Navigate to the Administration tab->General->About page or the About->RPDU in the web UI or via local/telnet/SSH interface(s) by logging in and checking the top right of the screen or entering the about command in the CLI.