Enter three phase readings to calculate phase-current imbalance percentage, PDU capacity and headroom, a fundamental neutral-current estimate where applicable, and what named load to move for a better balance. Use measured amps or plan line-to-neutral and line-to-line outlet-bank loading in amps, kW, or kVA.
kW uses the entered power factor. Wye A/B/C power uses derived line-to-neutral voltage; AB/BC/CA bank power uses line-to-line voltage.
Enter line-to-line voltage. The line-to-neutral value is derived for Wye guidance.
Rating and target apply to each line conductor. Confirm equipment and local requirements.
This is a site-policy threshold, not a universal limit. Up to half the threshold is Balanced, above half is Review, and above the threshold is Action required. This is current imbalance—not voltage unbalance or motor-specific NEMA guidance.
Measured line currents are the most direct input and may already include mixed Wye and Delta-connected loads.
Neutral current is a fundamental-frequency estimate only where a neutral is used. Prefer measured RMS neutral current for nonlinear IT loads.
Enter three values to compare utilization, headroom, and balance.
| Line | Input | Current | kVA | kW | Target headroom | Utilization | Status |
|---|---|---|---|---|---|---|---|
| No calculation yet. | |||||||
Add candidate rows to get a specific move.
Add movable device, outlet-bank, or circuit loads that are already included in the three totals above.
The current-imbalance method compares the largest absolute line-current deviation with the average. It is a planning indicator, not a universal PDU compliance limit and not the NEMA motor voltage-unbalance rule. Measured line currents are used directly. Wye line-to-neutral and line-line bank planning modes use the electrical assumptions below.
Wye voltage conversion
V_LN = V_LL / sqrt(3)
Load-to-current conversion
I = P x 1000 / (V x PF) for kW; I = S x 1000 / V for kVA. Use V_LN for A/B/C Wye loads and V_LL for AB/BC/CA banks.
Current imbalance
I_avg = (I_A + I_B + I_C) / 3
Unbalance % = 100 x max(|I_A - I_avg|, |I_B - I_avg|, |I_C - I_avg|) / I_avg
Fundamental neutral current estimate
I_N = sqrt(I_A^2 + I_B^2 + I_C^2 - I_A I_B - I_B I_C - I_C I_A)
Line-line bank currents
I_A = sqrt(I_AB^2 + I_CA^2 + I_AB I_CA); rotate the terms for B and C.
The neutral formula assumes a four-wire Wye system, 120-degree phase displacement, similar load-current phase angles, fundamental-frequency sinusoidal current, and linear loading. It omits triplen harmonics and phase-angle differences. The AB/BC/CA vector model likewise assumes the bank currents have the same power factor and similar current phase angles. For Delta, mixed wiring, or nonlinear loads, prefer simultaneous RMS measurements.
A metered PDU reads A = 34.5 A, B = 28.4 A, and C = 39.2 A.
I_avg = (34.5 + 28.4 + 39.2) / 3 = 34.03 A
maximum deviation = |28.4 - 34.03| = 5.63 A
imbalance = 100 x 5.63 / 34.03 = 16.55%
neutral estimate = 9.38 A
Move 5.4 A from C to B: A = 34.5 A, B = 33.8 A, C = 33.8 A.
recalculated imbalance = 1.37%; neutral estimate = 0.70 A
At 208 V, suppose AB = 16 A, BC = 8 A, and CA = 10 A. Vector combination gives line currents A = 22.72 A, B = 21.17 A, and C = 15.62 A; the current imbalance is 21.24% and total apparent power is 208 x (16 + 8 + 10) / 1000 = 7.07 kVA.
Moving a 4 A outlet group from AB to BC changes the banks to 12 A, 12 A, and 10 A. The projected line currents become 19.08 A, 20.78 A, and 19.08 A, reducing imbalance to 5.79% while total kVA stays the same.
There is no universal PDU compliance percentage. Use the selectable threshold as your site policy: this calculator labels up to half the threshold Balanced, up to the threshold Review, and above it Action required. Current imbalance is not voltage unbalance and is not motor-specific NEMA guidance.
Open the PDU metering screen for instantaneous or demand RMS current and record the three line conductors at the same time. Select Measured line currents and enter those three readings; do not substitute a total current or neutral reading.
Enter the nameplate line-to-line system voltage. For Wye line-to-neutral loads, the calculator derives V_LN = V_LL / sqrt(3). For AB/BC/CA banks it uses the entered line-to-line voltage directly.
An AB bank loads conductors A and B, BC loads B and C, and CA loads C and A. The calculator vector-combines bank currents assuming the same power factor and similar current phase angles; it does not simply add bank magnitudes to each conductor.
Three-phase total power can hide unequal conductor loading. A breaker pole, cord conductor, or outlet bank can reach its current limit before the PDU reaches its aggregate kW rating, so always review the highest phase and its headroom.
Calculate each physical PDU or feed separately, then repeat the assessment for the credible failover state in which one feed may carry the transferable load. Do not add two redundant feeds together and treat their combined headroom as available.
Use measured RMS neutral current whenever a meter provides it, especially for server and switch-mode loads, high current THD, shared neutrals, or conductor sizing. The estimate includes only fundamental-frequency imbalance and omits triplen harmonics.
Yes. In line-neutral mode, per-phase kW and kVA convert at line-to-neutral voltage. In line-line bank mode, bank kW and kVA convert at line-to-line voltage. kW conversion also uses the entered power factor.
No. It is an editable planning target, not a universal rule for every PDU. Confirm the circuit, breaker, cord, PDU listing, duty classification, local requirements, and manufacturer instructions for the installation.
Validation note: formulas were checked against balanced A/B/C currents (0% imbalance and 0 A fundamental neutral), the 34.5 / 28.4 / 39.2 A worked example, the 208 V AB/BC/CA vector example, power conversion at unity and non-unity power factor, overload boundaries, and optimizer moves that must conserve the entered load.
Use this tool for planning and field triage. Confirm results at the meter and against the PDU nameplate, breaker and outlet-bank ratings, conductor limits, OEM documentation, and applicable electrical requirements.
Measured phase current avoids the conversion assumptions needed for kW and kVA planning modes and captures whatever mixed load topology already exists.
One overloaded phase can trip or force derating even if the total three-phase kW still looks comfortable on paper.
A perfectly even average does not guarantee a lightly loaded neutral once nonlinear IT loads and harmonics enter the picture.
Shifting one or two single-phase devices from the heaviest phase to the lightest phase can often recover more headroom than expected.
Rack drawings and equipment labels are useful starting points, but live metering usually reveals a different operating balance than installed-nameplate totals suggest.
