3 Phase Load Calculation and Panel Load Balancing
Enter each load on a panel with its kVA and how it connects. The calculator spreads it across phases A, B, and C the way a panel schedule does, then shows per-phase kVA and amps, total connected load, and how far the heaviest phase sits above the average.
Method (standard panel schedule): a 3-phase load puts VA/3 on each of A, B, and C; a line-to-line load puts VA/2 on each of its two phases; a line-to-neutral load puts its full VA on its phase. Per-phase current = phase VA ÷ 120 V.
Phase A is heaviest and phase C is lightest. To get under the common 10% design target (not a code requirement), move a single-phase load from phase A to phase C. For example, moving Lighting (6 kVA) to L-N C brings imbalance to 15.2%.
Connected load is not demand load. Service and feeder sizing apply NEC Article 220 demand factors, the 125% factor for continuous loads, and the largest-motor adder. This tool balances connected load only; do not size a service or feeder from these totals.
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The 3 phase load calculation formula, step by step
A three-phase panel serves a mix of loads. Some draw from all three phases, some connect between two phases, and some connect from one phase to neutral. A load calculation assigns each one to the phases it actually loads, then totals each phase.
- 3-phase load: VA ÷ 3 on each of A, B, and C
- Line-to-line load: VA ÷ 2 on each of its two phases
- Line-to-neutral load: full VA on its one phase
Per-phase current is I_phase = phase VA ÷ V_LN. The equivalent balanced current for the whole panel is I = total VA ÷ (√3 × V_LL), and phase imbalance is (max phase − average) ÷ average × 100.
Worked example on 208Y/120 V
Using the four default loads above:
- RTU, 30 kVA, 3-phase: 10 kVA on each of A, B, and C
- Lighting, 6 kVA, L-N A: 6 kVA on A
- Receptacles, 4.5 kVA, L-N B: 4.5 kVA on B
- Water heater, 9 kVA, L-L A-B: 4.5 kVA on A and 4.5 kVA on B
Phase totals and currents:
- Phase A: 10 + 6 + 4.5 = 20.5 kVA, 20,500 ÷ 120 = 170.8 A
- Phase B: 10 + 4.5 + 4.5 = 19.0 kVA, 19,000 ÷ 120 = 158.3 A
- Phase C: 10 kVA, 10,000 ÷ 120 = 83.3 A
- Total connected load: 30 + 6 + 4.5 + 9 = 49.5 kVA
- Equivalent balanced current: 49,500 ÷ (1.732 × 208) = 137.4 A
- Imbalance: average = 49.5 ÷ 3 = 16.5 kVA, so (20.5 − 16.5) ÷ 16.5 × 100 = 24.2%
Phase A is heaviest and phase C is lightest. Moving the 6 kVA lighting load from L-N A to L-N C gives A = 14.5, B = 19.0, C = 16.0 kVA, and imbalance drops to (19.0 − 16.5) ÷ 16.5 = 15.2%. Further moves among smaller branch circuits would close the rest of the gap.
3 phase load calculation: frequently asked questions
How do you calculate 3 phase load?
List every load with its kVA and how it connects. Put one third of each three-phase load on each of phases A, B, and C, half of each line-to-line load on each of its two phases, and the full value of each line-to-neutral load on its one phase. Add up each phase, then divide by line-to-neutral voltage to get per-phase current. The sum of all loads is the total connected kVA.
What is the formula for 3 phase load in amps?
For a balanced load, I = (kVA × 1000) / (√3 × V_LL). A 49.5 kVA load at 208 V draws (49.5 × 1000) / (1.732 × 208) = 137.4 A. For an unbalanced panel, compute each phase separately: I_phase = phase VA / V_LN, so 20.5 kVA on phase A at 120 V is 170.8 A.
How do you balance a 3 phase panel?
Total the VA on each phase, find the heaviest and lightest phase, and move single-phase loads (line-to-neutral or line-to-line circuits) from the heaviest phase toward the lightest until the phases are close. Many designers aim for every phase within about 10% of the average. That is a common design target, not an NEC requirement.
What is the difference between connected load and demand load?
Connected load is the nameplate sum of everything wired to the panel. Demand load is what the code expects to be on at once, after NEC Article 220 demand factors, the 125% factor for continuous loads, and the largest-motor adder. Services and feeders are sized from the demand load calculation, not the connected total.
Why are line-to-line loads split half on each phase?
A single-phase load connected between two phases draws its current through both of them, so panel schedules assign half its VA to each. This is a bookkeeping convention for balancing. The actual line current of a single line-to-line load is VA / V_LL, which on 208 V is about 15% higher than VA/2 / 120, so check conductor sizing separately.
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