Phase balancing calculator

Field use cases

Use this calculator when a switchboard, tenancy board, workshop board, alteration job or maintenance record needs a quick view of how evenly single-phase loads are spread across L1, L2 and L3. It is the sort of worksheet that helps before a load schedule is finalised, before an extra circuit is assigned to a phase, or before someone decides whether a load move is worth checking in detail.

The page is most useful when the loads already exist as phase currents. That might be a schedule derived from circuits, a measured board record, or a planning sheet that already converted connected loads into amps. The result does not need the whole installation story to be useful, but it does need a consistent current basis. If the three numbers do not describe the same operating condition, the worksheet can look tidy while the board is still poorly understood.

This calculator does not replace engineering judgement. It provides a structured starting point for phase-loading review.

Data to confirm before balancing decisions

The strongest input is a set of phase currents that all belong to the same board and the same operating condition. That can mean one measured snapshot, one planning worksheet, or one schedule row set. What it should not mean is a mixture of old and new values, a mix of connected and demand current, or a blend of current from different operating times without saying so.

If one phase is entered as zero while the others carry load, check whether the zero is deliberate. A deliberately unassigned phase can be legitimate in a planning sketch. A zero that came from a missing row is not.

Phase review matrix

The main reading is not just the percentage. The main reading is the combination of average load, spread, highest phase and lowest phase.

The transfer hint is intentionally conservative and simple. It is a planning value that points the reviewer toward the direction of change. It does not decide whether a circuit can actually move, whether the move is technically suitable, or whether the board has the spare ways and protection arrangement to support that change.

Worked switchboard example

A workshop distribution board has entered currents of 64 A on L1, 52 A on L2 and 44 A on L3. The reviewer has set a 10% threshold for this worksheet. The average phase load is 53.33 A.

L1 is 10.67 A above average, L2 is 1.33 A below average and L3 is 9.33 A below average. The imbalance percentage is 20.0%, because the largest absolute deviation from average is 10.67 A and the average is 53.33 A. The spread between the highest and lowest phase is 20 A, so the transfer hint is 10 A.

The neutral estimate is smaller than the phase currents because these are entered as linear loads with a phasor relationship. That number is useful as a reminder that neutral behaviour may still need attention, but it is not a substitute for measured current or harmonic review.

In practice, the question after this example is not whether the board has been fully reviewed. The real question is whether the board schedule deserves a load move review before the record is used in a larger design or maintenance decision. For a workshop, that may mean looking at the phase assigned to fixed tools, socket outlets, air conditioning, lighting and any added single-phase equipment. For a tenancy, it may mean deciding whether the new fit-out should be reallocated before the board record is frozen.

Review workflow

Define the load boundary before interpreting the percentage. Decide whether the worksheet covers a whole board, a section of the board, a tenancy or a specific alteration record. Then confirm whether the phase currents are planned or measured. That is the point where many worksheets go wrong: the numbers are valid, but the operating condition is not recorded.

Next, read the average and spread before reading the percentage. The average tells you where the centre of the worksheet sits. The spread tells you how far apart the phase currents are. The percentage turns that spread into a threshold check. Together they tell a much clearer story than any one value on its own.

If the imbalance is above the entered threshold, the right response is a review, not an automatic phase move. Check whether a circuit can move at all, whether the existing board space and protection allow the change, and whether the result should be carried into a maximum-demand worksheet. If the imbalance is within threshold, keep the record but do not assume that the rest of the installation is automatically fine.

How this differs from voltage unbalance

This calculator uses current values that you already have in a board or load schedule. Voltage unbalance uses measured voltages and belongs to a different question. It is about supply quality, not load allocation.

Because the inputs are different, the conclusions are different. A board can have even load allocation and still show a voltage quality issue. A board can also show uneven load allocation without any voltage unbalance result being measured yet. Treat them as related, not interchangeable.

Neutral-current note

The linear neutral estimate is included because practitioners often want a quick context value after the phase spread is known. It is not a neutral conductor design check. It excludes triplen harmonics, non-linear loads, distorted current waveforms and installation-specific conditions.

Use the neutral estimate as a signal to ask better questions. Is the board mainly linear? Are the loads dominated by drives, electronic gear or chargers? Has the site already seen neutral heating or nuisance behaviour? If any of those questions matter, move from this worksheet to measured review or a more specific power-quality check.

The estimate becomes most useful when the phase schedule is part of a wider review record. In that record, you can see whether the same board also needs maximum demand, current conversion, cable sizing or voltage unbalance review. That context is what turns the worksheet into a working tool instead of a number on its own.

When to use the result with other calculators

If the phase values came from a load schedule that still needs whole-board review, carry the row into the maximum-demand calculator next. If the currents still need to be derived from W, kW, VA or kVA, use the load current calculator first. If the real question is whether the supply itself is showing measured voltage deviation, treat it as a measured voltage or power-quality review rather than a phase-allocation worksheet.

The most useful sequence is often:

1. Convert a load to current if needed.
2. Check the balance across L1, L2 and L3.
3. Revisit maximum demand if the board arrangement changes.
4. Only then decide whether cable, protection or supply review needs to move.

That sequence keeps the worksheet within its intended role. It prevents phase balancing from being used as a shortcut around the larger installation questions.

Stop points

• The currents do not belong to the same board or the same operating condition.
• The threshold is copied without a project basis.
• The neutral estimate is being treated as a neutral design result.
• The transfer hint is being treated as a circuit movement instruction.
• The result is being used as a voltage unbalance result.
• The board needs maximum demand, cable sizing, protection or DNSP review before the phase allocation can be trusted.

When one of those stop points appears, the worksheet is still useful. It just means the follow-up review belongs somewhere else; it does not justify a stronger claim from this page.