Total comsumption

[Anonymous user]

Hello,
I am trying to know the total comsuption per rack in my server room.
In each rack I have 2 PDU, one on the generator line and the other on the APC UPS.
Each PDU has one breaker in the UPS.
With a clamp meter, I was messuring each phase on the braker and I have got 2.9Amp on L1, 3Amp on L2 and 4 on L4.
My question:

Is the total Amp for the rack (2.9 + 3 + 4)/3 * 1.73 ? is not, How can I messure this?

Thanks

[Anonymous user]

If deriving power from a three-phase UPS or PDU power source, isn't the individual phase 120VAC, and phase-to-phaes 208VAC?
Would 208 vice 240 need to be used in your I X E = Power calculations?

[Anonymous user]

Thank you for your answer.

The voltage is 208v but I'm not sure the total comsuption is the linear adding of each value for each phase. I think it must be corrected in the case of a 3 phase system by the cube root of 3 (1.73), Am I correct?

Thanks

[Anonymous user]

The previous power formula looks like the standard P=I X E, where P(in Watts) = I(in Amps) X E(120/208/240VAC). My note indicated a variance in the formula depending upon what the value of E is in your facility (208 or 240VAC). If connecting between two phases provides ?3 or 173% of the single-phase voltage because the out-of-phase (120 degree lead/lag) waveforms add to provide a higher peak voltage in the resulting waveform. Such connection is referred to as a line to line connection and is usually done with a two pole circuit breaker. This kind of connection is typically used for high power appliances or equipment. Total Power would be cumulative, per branch or circuit, based upon total current.

[Anonymous user]

Sorry for late reply,

I gave an example based on conditions in my country which is 240VAC (Single Phase) and 415VAC (Phase to Phase)

For your situation just substitute 240VAC with 120VAC (Single Phase) or 208VAC (Phase to Phase)

Readings you took are based on individual phases
L1-N = 2.98Amps
L2-N = 3 Amps
L3-N = 4 Amps

To get total consumption for three single phases:
(Amp^L1^ + Amp^L2^ + Amp^L3^) x Volt^L-N^

(2.9 + 3 + 4) x 120 = 1188Watts

Reverse engineering: Assuming load balanced across all phases:

I = P / (?3 x V^L-L^)

1188 / (1.73 x 208) = 3.3Amps per phase.


Regards,
C.L.Chee

[Anonymous user · Accepted solution]

Hello,
I am trying to know the total comsuption per rack in my server room.
In each rack I have 2 PDU, one on the generator line and the other on the APC UPS.
Each PDU has one breaker in the UPS.
With a clamp meter, I was messuring each phase on the braker and I have got 2.9Amp on L1, 3Amp on L2 and 4 on L4.
My question:

Is the total Amp for the rack (2.9 + 3 + 4)/3 * 1.73 ? is not, How can I messure this?

Thanks