Neutral current calculator
Estimate linear-load neutral current from entered L1, L2 and L3 current records for Australian load review.
IN = sqrt(IL1^2 + IL2^2 + IL3^2 - IL1 x IL2 - IL2 x IL3 - IL3 x IL1); margin = IN_limit - IN; neutral_% = IN / max(IL1, IL2, IL3) x 100- Phase currents are entered by the user.
- The formula assumes sinusoidal linear currents separated by 120 degrees.
- The review limit is entered by the user.
- Harmonic neutral current and conductor selection are outside this worksheet.
| Variable | Meaning | Unit | Use |
|---|---|---|---|
| IL1 | L1 current | A | Entered current record on L1. |
| IL2 | L2 current | A | Entered current record on L2. |
| IL3 | L3 current | A | Entered current record on L3. |
| IN | Neutral current estimate | A | Calculated linear-load neutral current. |
| IN_limit | Neutral review limit | A | Entered comparison value for the worksheet. |
| neutral_% | Neutral percentage | % | Neutral estimate divided by the highest entered phase current. |
More
Neutral current calculator technical guide
Estimate linear-load neutral current from entered L1, L2 and L3 current records for Australian load review.
Use this calculator when L1, L2 and L3 current records are already known and the question is how large the linear-load neutral current estimate is. It is a worksheet for board records, maintenance notes, alteration reviews and load-schedule checks, not a conductor-sizing or harmonic study tool.
Field Use Cases
| Work setting | Real question | Useful action from this page |
|---|---|---|
| Board measurement | What neutral estimate follows from the three entered currents? | Calculate the 120-degree linear-load phasor result. |
| Phase-balancing review | Does the neutral estimate add context to an uneven phase record? | Keep neutral current beside phase spread and highest phase. |
| Maintenance record | Which measurement set produced the estimate? | Record the board reference and review limit. |
| Load schedule review | Are planned phase currents producing a material neutral estimate? | Compare the estimate with an entered review value. |
| Power-quality handoff | Is the load type likely to make the linear estimate incomplete? | Move harmonic or distorted-current questions to power-quality review. |
This page is intentionally narrow. It does not model triplen harmonics, neutral heating, conductor installation conditions or product-specific limits.
Data Checklist
| Value | Where it normally comes from | Stop if |
|---|---|---|
| Board reference | Distribution board, switchboard, tenancy or measurement record | The three currents do not belong to the same boundary. |
| L1, L2, L3 currents | Load schedule, measured current record or planning worksheet | The currents come from different operating states. |
| Review limit | Project worksheet, engineering note or measurement review value | The limit has no source basis. |
| Load type context | Site observation, equipment list or measurement record | Non-linear loads dominate but harmonic data is missing. |
| Follow-up task | Phase balancing, load sharing or power-quality review | The result is being treated as a final conductor decision. |
Comparable inputs matter more than polished arithmetic. Three good current readings from the same operating condition are more useful than mixed values from different reports.
Review Workflow
| Step | Record to check | Move to |
|---|---|---|
| Define the measurement boundary | Board or schedule reference | Enter L1, L2 and L3 currents. |
| Confirm current basis | Same operating state and measurement basis | Calculate the linear estimate. |
| Compare the limit | User-entered neutral review value | Read the review margin. |
| Check load type | Linear or non-linear load context | Decide whether harmonic review is needed. |
| Choose follow-up | Phase spread, row allocation or power-quality measurement | Use the linked calculator that owns that task. |
If the estimate is above the entered review limit, treat it as a prompt to check the source values and the load type. It does not say the neutral is suitable or unsuitable by itself.
Worked neutral-current record
A board record has entered currents of 86 A on L1, 64 A on L2 and 52 A on L3. The reviewer enters a 30 A neutral review limit for this worksheet.
The linear-load neutral-current estimate is 29.87 A. The average phase current is 67.33 A, the highest phase is L1, and the neutral current is 34.73% of the highest phase current. The review margin is 0.13 A below the entered limit.
| Value | Result |
|---|---|
| L1 current | 86 A |
| L2 current | 64 A |
| L3 current | 52 A |
| Neutral estimate | 29.87 A |
| Highest phase | L1 |
| Neutral to highest phase | 34.73% |
| Review margin | 0.13 A |
The narrow margin means the current record deserves careful context. Check whether the loads are mostly linear, whether the measurement state is representative and whether harmonic data should be reviewed.
Method boundary
| Method element | What this page does | What remains outside |
|---|---|---|
| Phase-current record | Uses entered L1, L2 and L3 current values. | Measurement quality and operating-state selection. |
| Phasor relationship | Applies the 120-degree linear-load neutral-current formula. | Harmonic current and distorted waveform analysis. |
| Review margin | Compares the estimate with an entered limit. | Neutral conductor selection and installation review. |
| Follow-up routing | Links to phase balancing, load sharing and harmonic review. | Project decisions and formal documentation. |
Keeping this boundary clear lets the page support phase-loading work without pretending to own every neutral-current question.
Stop points
- The three phase currents do not belong to the same board, time window or operating condition.
- The load is dominated by drives, electronic gear, chargers or other non-linear equipment without measured harmonic context.
- The review limit has no source record.
- The result is being used as a neutral conductor selection.
- The current record should first be checked with phase balancing or load sharing.
When one of these stop points appears, keep the worksheet as a question record and move the follow-up to the calculator or project review that owns it.
Distribution board phase-current record
A three-phase board has entered single-phase line-current readings from a load review.
- Board reference
- DB-N-1
- Phase currents
- 86 A / 64 A / 52 A
- Neutral review limit
- 30 A
- Neutral estimate29.87 A
- Percent of highest phase34.73%
- Review margin0.13 A
Use the status as a worksheet prompt, not a conductor decision.
The neutral estimate sits just below the entered review limit, so the record can move into broader phase and supply review.
- Currents are RMS line-current values.
- The worksheet uses a 120-degree linear-load phasor basis.
- Harmonic neutral current is outside this page.
Balanced comparison record
A balanced three-phase load record checks that equal phase currents resolve to a near-zero linear-load neutral estimate.
- Board reference
- DB-BALANCED
- Phase currents
- 80 A / 80 A / 80 A
- Neutral review limit
- 30 A
- Neutral estimate0 A
- Percent of highest phase0%
- Review margin30 A
Use the status as a worksheet prompt, not a conductor decision.
Balanced entered phase currents produce a 0 A neutral-current estimate on this basis.
- The three phase currents are entered on the same measurement basis.
- Only the fundamental linear-load relationship is calculated.
- Instrument and project records still govern review.
High imbalance prompt
A board alteration record shows a larger phase spread and a neutral estimate above the entered review limit.
- Board reference
- DB-REVIEW
- Phase currents
- 72 A / 44 A / 36 A
- Neutral review limit
- 25 A
- Neutral estimate32.74 A
- Percent of highest phase45.47%
- Review margin-7.74 A
Use the status as a worksheet prompt, not a conductor decision.
The entered values should be reviewed before the worksheet is used for downstream capacity or phase allocation decisions.
- The limit is entered by the user.
- Neutral conductor selection is not decided here.
- Non-linear load harmonic contribution needs a separate power-quality worksheet.