Power Calcs on RPP with single phase 120V and 208V loads

[Randall-EE98]

I am attempting to identify why DCIM, UPS, RPP loads are producing varying values in calculations and metering. The loads are both 120V and 208V single phase from electronic devices (computers and network electronics) connected to 120V, 208V single phase and 208V 3-phase power strips. The 208V single & 3-phase power strips have C13 & C19 receptacles, so the electrical device loads are 208V single phase loads however fed from an upstream 2-pole or 3-pole branch circuit breakers. The RPP's have 4 225A, 42 slot panels each. The RPP display provides the Amps for A, B, C & neutral for each panel. The branch circuit metering is not accurate (incorrectly wired CT's, incorrect schedules etc. so DCIM calcs are not correct). That is what I am trying to remediate. The metering data that should be relatively accurate is the RPP A, B, C, N values and the UPS(s) total power and phase Amps. Power factor is close to 1 (computers are efficient heaters).

Here are the values from 2 panels: #1 L1-22A, L2-32A, L3-32A, N-10A #2 L1-37A, L2-39A, L3-25A, N-3A

Is there enough info without branch circuit Amps to calculate the total power consumption per panel? Thanks for any help.

 

[wwhitney]

Your post has a bunch of acronyms that are unclear to me, but I understand you to be asking the following question:

Suppose we have a 208Y/120V system, and a collection of single phase (2-wire), power factor 1 loads, both 120V and 208V, and they are connected across A, B, C, and N in an unknown fashion. We measure the total currents A, B, C, and N, in magnitude only, with no phase information. Can we exactly determine the total power used by the loads?

I believe in general the answer is no, not without further information. Here's an example, with the individual load currents given:

Case 1: A-B = 10, A-N = 10, B-N = 10, C-N = 5. Then the current on A from B is 30 degrees apart from the current on A from N, and the magnitude of the sum current on A is 10 * sqrt(2+sqrt(3)) = 19.3. Likewise on B we have 19.3. C is obviously 5, and N is also 5. The power is 10*208 + (10+10+5)*120 = 5,080W.

Case 2: A-B = 19.3, C-N = 5. Then the line currents are the same as case 1. But now the power is only 19.3*208 + 5*120 = 4,614W.

So different configurations of loads with different total powers can give identical load currents. Although the discrepancy is not too large, so you can probably get an answer within 10% or so by just guessing a combination of loads that gives the observed currents, and just calculating the power used by the guessed combination of loads.

Cheers, Wayne