Commercial Phase Allocation Calculator

A commercial phase allocation calculator compares known VA assigned to Phase A load, Phase B load, and Phase C load. It produces the phase-loading imbalance in VA and percent, identifies the highest- and lowest-loaded phases, estimates each phase current from the entered Phase voltage basis, and shows a Suggested transfer screen for preliminary load redistribution.

This calculation is useful early in commercial panel, feeder, and distribution design when circuit or equipment loads have already been allocated by phase. The result can flag a phase that may drive feeder ampacity, overcurrent-device review, bus loading, voltage-drop review, raceway layout, or future circuit placement decisions.

It does not perform panel balancing automatically and does not approve the panelboard, feeder, branch circuit, or service design.

Related phase-planning tools: Three-Phase Load Balance Calculator, Panel Schedule Calculator, and Commercial Load Calculator.

Phase Allocation and Load Imbalance

A balanced three-phase allocation places approximately equal VA on all three phase conductors. When one phase carries materially more VA than the others, that phase has the highest current estimate and can become the limiting phase for later design work.

The calculator uses these input fields:

Input	Electrical use
Phase A load (VA)	Total apparent power presently allocated to Phase A
Phase B load (VA)	Total apparent power presently allocated to Phase B
Phase C load (VA)	Total apparent power presently allocated to Phase C
Phase voltage basis (V)	Voltage used to convert each entered phase VA into a phase-current estimate

VA is appropriate for this screen because it allows connected loads with different power factors to be collected into a common apparent-power allocation. The current conversion is made separately for each phase using the entered voltage basis:

\(\displaystyle I_{\text{phase}} = \frac{VA_{\text{phase}}}{V_{\text{phase basis}}}\)

The entered voltage is a calculation basis, not a determination of the actual system configuration. Confirm whether the equipment and loads are line-to-neutral or line-to-line before using the current estimate in feeder, branch-circuit, conductor, or equipment review.

Calculation Results

The calculator reports the following allocation values:

Result	Calculation
Total load	VA_A + VA_B + VA_C
Average phase load	frac{VA_A + VA_B + VA_C}{3}
Maximum phase load	Largest of the three entered phase VA values
Minimum phase load	Smallest of the three entered phase VA values
Maximum phase deviation	max(|VA_A - VA_avg|, |VA_B - VA_avg|, |VA_C - VA_avg|)
Imbalance estimate	maximum deviation / average phase load x 100%
Suggested transfer screen	(maximum phase load - minimum phase load) / 2
Phase A/B/C current estimate	VA_{text{phase}} div V_{text{phase basis}}

The Maximum phase deviation is the largest absolute difference between an entered phase load and the average phase load. The Imbalance estimate expresses that maximum absolute deviation as a percentage of the average phase load.

The Suggested transfer screen is half the difference between the highest and lowest entered phase loads. It is a screening value, not a directive to move a specific circuit. A practical transfer must be selected from actual branch-circuit, equipment, control, operating, and voltage constraints.

Calculation Example

Enter the following known phase allocations:

Input	Value
Phase A load (VA)	24,000 VA
Phase B load (VA)	18,000 VA
Phase C load (VA)	12,000 VA
Phase voltage basis (V)	480 V

The total allocated load is:

\(\displaystyle 24{,}000 + 18{,}000 + 12{,}000 = 54{,}000 \text{VA}\)

The average phase load is:

\(\displaystyle \frac{54{,}000}{3} = 18{,}000 \text{VA}\)

Phase A is the maximum phase load at 24,000 VA, while Phase C is the minimum phase load at 12,000 VA. The maximum phase deviation is:

\(\displaystyle 24{,}000 - 18{,}000 = 6{,}000 \text{VA}\)

The imbalance estimate is:

\(\displaystyle \frac{6{,}000}{18{,}000} \times 100 = 33.3333\%\)

The per-phase current estimates using the 480 V basis are:

\(\displaystyle I_A = \frac{24{,}000}{480} = 50 \text{A}\)

\(\displaystyle I_B = \frac{18{,}000}{480} = 37.5 \text{A}\)

\(\displaystyle I_C = \frac{12{,}000}{480} = 25 \text{A}\)

Result	Value
Total load	54,000 VA
Average phase load	18,000 VA
Maximum phase load	24,000 VA
Minimum phase load	12,000 VA
Maximum phase deviation	6,000 VA
Imbalance estimate	33.3333%
Suggested transfer screen	6,000 VA
Phase A current estimate	50 A
Phase B current estimate	37.5 A
Phase C current estimate	25 A
Voltage used	480 V

For preliminary allocation review, the result identifies Phase A as the phase to investigate and reports a 6,000 VA maximum deviation. The 6,000 VA transfer screen is half the difference between the highest and lowest phase loads; moving a suitable 6,000 VA single-phase allocation from Phase A to Phase C would produce three 18,000 VA phase totals in the arithmetic model. Actual circuit moves may not be available in that exact size, and a proposed reassignment must preserve equipment operation and circuit compatibility.

Use in Feeder and Panel Review

The highest phase current estimate is often the starting point for subsequent feeder or panel review. In the example, Phase A’s 50 A estimate is higher than Phase B’s 37.5 A and Phase C’s 25 A. If the phase allocations represent a feeder load study, later calculations may need to consider whether the highest loaded phase affects conductor ampacity, terminal rating, overcurrent protection, bus rating, disconnect rating, voltage drop, or available panel capacity.

A phase allocation review can also support practical layout decisions:

• Locate candidate single-phase branch circuits that can be reassigned without affecting multiwire circuits, control circuits, equipment listings, or operating requirements.
• Check whether a heavily loaded phase produces a less favorable voltage-drop condition on a long feeder or branch circuit.
• Review whether added circuits, tenant loads, HVAC equipment, receptacle loads, or lighting loads are concentrating on one phase.
• Compare actual circuit and load schedules with the assumed VA values before changing panel labels or circuit assignments.
• Keep three-phase loads and equipment requirements separate from single-phase load-shifting decisions.

Field and Code Limits

The worksheet performs phase-allocation arithmetic only. It does not apply demand factors, diversity, continuous-load treatment, motor rules, nonlinear-load behavior, neutral loading, harmonics, power factor, conductor ampacity, AWG or kcmil selection, insulation temperature rating, terminal limitations, adjustment factors for current-carrying conductors, correction factors for ambient temperature, raceway fill, voltage-drop limits, overcurrent protection, equipment ratings, utility requirements, or AHJ acceptance.

Do not use the current estimates as final conductor-sizing values. A feeder or branch-circuit design still requires the applicable load calculation, conductor ampacity evaluation, terminal rating review, protection coordination, equipment documentation, installation conditions, and code requirements. Verify actual voltage, phase configuration, load type, operating coincidence, and installed circuit arrangement before relocating loads or modifying a panel schedule.