Three-phase load sharing calculator
Distribute entered single-phase load rows across L1, L2 and L3 for an Australian load-sharing worksheet.
Irow = Iload x quantity; PhaseTotal = sum(Irow assigned to each phase); Spread = max(PhaseTotal) - min(PhaseTotal); margin = target_spread - Spread- Rows are allocated in the order entered.
- Fixed-phase rows stay on the entered phase.
- Unassigned rows are placed on the current lowest phase total.
- The result is a worksheet prompt, not a circuit instruction.
| Variable | Meaning | Unit | Use |
|---|---|---|---|
| Iload | Row current | A | Entered current for one item in the load row. |
| Irow | Row load | A | Row current multiplied by quantity. |
| PhaseTotal | Phase total | A | Sum of row loads allocated to one phase. |
| Spread | Phase spread | A | Highest phase total minus lowest phase total. |
| target_spread | Target spread | A | Entered comparison value for the worksheet. |
| margin | Spread margin | A | Target spread minus calculated spread. |
More
Three-phase load sharing calculator technical guide
Distribute entered single-phase load rows across L1, L2 and L3 for an Australian load-sharing worksheet.
Use this calculator when single-phase load rows need a transparent first allocation across L1, L2 and L3. It is useful for a board schedule, tenancy fit-out, workshop alteration or early load list where some rows are fixed and others are still available for allocation review.
Field Use Cases
| Work setting | Real question | Useful action from this page |
|---|---|---|
| New board schedule | Where do unassigned single-phase rows land? | Allocate each unassigned row to the current lowest phase. |
| Existing board addition | Which rows are already fixed to a phase? | Keep fixed-phase rows on L1, L2 or L3. |
| Tenancy planning | How far apart are the entered phase totals? | Compare highest and lowest phase totals. |
| Phase review | Which totals should move into the phase balancing calculator? | Export L1, L2 and L3 totals as a worksheet record. |
| Load schedule handoff | Which row order drove the result? | Keep row labels, quantities and phase labels visible. |
The calculator uses a simple visible allocation method. It should not be treated as a switchboard layout engine.
Data checklist
| Value | Where it normally comes from | Stop if |
|---|---|---|
| Schedule reference | Board schedule, tenancy plan or alteration record | The row boundary is unclear. |
| Row current | Load-current calculation, equipment data or schedule value | Rows use different current bases without labels. |
| Quantity | Circuit list, outlet group or equipment count | Quantity combines unrelated loads. |
| Fixed phase | Existing board record or proposed phase assignment | Fixed rows are guessed. |
| Target spread | Project review value or engineering worksheet target | The target has no source basis. |
The method is intentionally transparent. A later reviewer can see which row was allocated first and why the phase totals ended where they did.
Review Workflow
| Step | Record to check | Move to |
|---|---|---|
| Define row list | Board or schedule reference | Enter row currents and quantities. |
| Mark fixed rows | Existing or proposed phase labels | Leave unassigned rows for allocation. |
| Allocate rows | Current lowest phase at each row | Read phase totals and spread. |
| Compare spread | Entered target spread | Use phase balancing if totals need review. |
| Resolve row order | Large or sensitive rows | Return to the schedule before using the totals. |
If the spread is above the entered target, the result is a review prompt. It does not decide which circuit should move or whether the board arrangement is suitable.
Worked load-sharing record
A workshop schedule includes a 64 A outlet row, an 18 A office air-conditioning row, a 12 A comms row and a 20 A existing row fixed to L2. The target spread is 12 A.
The worksheet allocates the first unassigned row to L1, the second to L2 and the third to L3. The fixed row also stays on L2. The final phase totals are 64 A on L1, 38 A on L2 and 12 A on L3. The spread is 52 A, so the result is above the entered target.
| Value | Result |
|---|---|
| Total row load | 114 A |
| L1 total | 64 A |
| L2 total | 38 A |
| L3 total | 12 A |
| Highest phase | L1 |
| Lowest phase | L3 |
| Spread | 52 A |
| Spread margin | -40 A |
The result is useful because the large first row is visible. A reviewer can decide whether that row should be split, reallocated, or left as a known project constraint.
Method boundary
| Method element | What this page does | What remains outside |
|---|---|---|
| Row load | Multiplies current by quantity. | Choosing the correct source current. |
| Fixed phase | Keeps rows on an entered phase. | Confirming real board space and circuit arrangement. |
| Unassigned phase | Places rows on the current lowest phase total. | Optimised scheduling or detailed design. |
| Spread result | Compares highest and lowest phase totals. | Phase movement, maximum demand and protection review. |
This boundary keeps the page useful as a row-allocation worksheet and stops it from becoming a hidden design rule.
Stop points
- Fixed-phase labels are unknown or temporary.
- A large row is entered first and dominates the result without review.
- Row currents come from different operating states or source types.
- The target spread is copied without project context.
- The result is being treated as an instruction to move circuits.
- Maximum demand, neutral current, switchboard space or protection review is needed before the row allocation can be used.
When a stop point appears, keep the exported worksheet as a schedule question and resolve the row source before carrying totals downstream.
Workshop single-phase distribution
A load schedule has three movable rows and one existing fixed L2 row.
- Schedule reference
- LS-SHARE-1
- Rows
- 4
- Target spread
- 12 A
- Highest phaseL1
- Lowest phaseL3
- Spread52 A
Use the allocation as a worksheet prompt before editing a real circuit schedule.
The first large row still dominates L1, so the result remains a review prompt rather than a phase-movement instruction.
- Rows are allocated in the entered order.
- Fixed-phase rows stay on their entered phase.
- Circuit movement remains a separate review.
Balanced row set
Three equal single-phase rows are distributed evenly across L1, L2 and L3.
- Schedule reference
- LS-BALANCED
- Rows
- 3
- Target spread
- 8 A
- Highest phaseL1
- Lowest phaseL3
- Spread0 A
Use the allocation as a worksheet prompt before editing a real circuit schedule.
The simple row set lands evenly on the three phases within the entered spread target.
- Each row represents a single-phase load group.
- The target spread is entered by the user.
- No maximum-demand rule is embedded.
Small board addition
A small board addition has two fixed rows and one movable allowance row.
- Schedule reference
- LS-SMALL
- Rows
- 3
- Target spread
- 15 A
- Highest phaseL1
- Lowest phaseL3
- Spread8 A
Use the allocation as a worksheet prompt before editing a real circuit schedule.
The movable row is placed on the lowest current phase, which keeps the spread visible for review.
- Only three displayed rows are included.
- Loads are entered on the same current basis.
- Protection and cable checks stay separate.