Switchboard demand margin calculator
Compare Australian switchboard rating, calculated demand and future allowance to show remaining demand margin.
Keep the selected inputs, source record, result basis and review boundary with the project documents before relying on the calculation.
Iplanned = Idemand + Ifuture;MarginA = Irating - Iplanned;UsedPercent = Iplanned / Irating x 100;MarginPercent = MarginA / Irating x 100;TargetMarginA = Irating x TargetPercent / 100- Switchboard rating is user-entered.
- Calculated demand comes from a source worksheet.
- Future allowance must use the same current basis.
- Target margin is a worksheet comparison value.
| Variable | Meaning | Unit | Use |
|---|---|---|---|
| Irating | Switchboard rating | A | Entered board rating comparison value. |
| Idemand | Calculated demand | A | Entered demand value from a source worksheet. |
| Ifuture | Future allowance | A | Entered future allowance current. |
| Iplanned | Planned demand | A | Calculated demand plus future allowance. |
| MarginA | Remaining margin | A | Switchboard rating minus planned demand. |
| UsedPercent | Used capacity | % | Planned demand divided by switchboard rating. |
| TargetPercent | Target margin | % | Entered margin target as a percentage of rating. |
| TargetMarginA | Target margin current | A | Rating multiplied by target percentage. |
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Switchboard demand margin calculator technical guide
Compare entered switchboard rating, calculated demand and future allowance for an Australian demand margin worksheet.
Use this calculator when a switchboard demand record needs a clear margin calculation. It keeps calculated demand, future allowance and target margin separate so the result can be checked without hiding the assumptions inside a single number.
Field Use Cases
| Work setting | Real question | Useful action from this page |
|---|---|---|
| Board review | How much margin remains after calculated demand and allowance? | Compare planned demand with entered rating. |
| Future load planning | How much does a future allowance reduce margin? | Keep future allowance separate from present demand. |
| Project record | What percentage of the board rating is used? | Read used capacity and margin percentage. |
| Scope change | Does a revised allowance cross the target margin? | Update the allowance and target margin fields. |
| Supply discussion | Is this a board question or a site supply question? | Route broader capacity checks to supply capacity planning. |
This worksheet is deliberately narrower than a full switchboard review. It does not consider enclosure temperature, protective devices, cable entries, physical space or other project-specific checks.
Data checklist
| Value | Where it normally comes from | Stop if |
|---|---|---|
| Board reference | Switchboard schedule, drawing or asset tag | The board cannot be identified. |
| Switchboard rating | Switchboard documentation or project record | The rating value has no source. |
| Calculated demand | Maximum-demand worksheet, measured record or design value | It uses a different current basis. |
| Future allowance | Committed project scope or recorded allowance | It is speculative but not labelled. |
| Target margin | Project comparison value | It is being treated as an authority rule. |
The input values should be traceable before the result is reused. If the calculated demand is still uncertain, use the maximum demand calculator first.
Review Workflow
| Step | Record to check | Move to |
|---|---|---|
| Identify board | Board reference and rating source | Enter switchboard rating. |
| Confirm demand value | Demand worksheet or measured record | Enter calculated demand. |
| Separate future load | Committed allowance or project note | Enter future allowance. |
| Compare margin | Target margin percentage | Read remaining margin and margin above target. |
| Choose detailed check | Board spare capacity, maximum demand or supply capacity | Use the linked calculator that owns that question. |
If the remaining margin is below the entered target, the output should prompt a source check and project review, not a single automatic conclusion.
Worked demand margin record
A main switchboard record enters a 250 A rating, 184 A calculated demand, 28 A future allowance and a 12% target margin.
The planned demand is 212 A. The remaining margin is 38 A, used capacity is 84.8% and the margin percentage is 15.2%. The target margin is 30 A, leaving 8 A above the entered target.
| Value | Result |
|---|---|
| Switchboard rating | 250 A |
| Calculated demand | 184 A |
| Future allowance | 28 A |
| Planned demand | 212 A |
| Remaining margin | 38 A |
| Used capacity | 84.8% |
| Margin above target | 8 A |
The result is useful because present demand and future allowance remain visible. If the allowance changes, the margin can be updated without rebuilding the demand worksheet.
Method boundary
| Method element | What this page does | What remains outside |
|---|---|---|
| Planned demand | Adds calculated demand and future allowance. | Choosing the demand calculation method. |
| Remaining margin | Subtracts planned demand from entered rating. | Deciding switchboard suitability. |
| Used capacity | Divides planned demand by entered rating. | Assessing thermal, protective-device or enclosure limits. |
| Target margin | Converts entered percentage to amps and compares margin. | DNSP, project and equipment decisions. |
The calculator is a comparison worksheet. It should sit beside, not replace, the underlying demand and switchboard records.
Stop points
- The switchboard rating has no source record.
- The demand value is not documented or uses a different current basis.
- Future allowance is mixed into calculated demand without a label.
- Target margin is being treated as a rule instead of a comparison value.
- The result is being used as a complete switchboard decision.
- The real task is spare capacity, supply capacity or maximum demand.
When a stop point appears, keep the result as a question for review and resolve the source value before carrying the margin forward.
Main switchboard margin
A main switchboard record compares calculated demand and a future allowance with an entered board rating.
- Board reference
- MSB-1
- Switchboard rating
- 250 A
- Target margin
- 12%
- Planned demand212 A
- Remaining margin38 A
- Margin percent15.2%
Use the status as a demand-margin prompt before detailed board review.
The remaining margin is above the entered target, so the value can be carried into the project review record.
- Board rating is user-entered.
- Calculated demand comes from a separate worksheet.
- Future allowance is deliberately recorded.
Constrained board margin
A larger future allowance pushes the remaining margin below the entered target value.
- Board reference
- MSB-REVIEW
- Switchboard rating
- 250 A
- Target margin
- 12%
- Planned demand229 A
- Remaining margin21 A
- Margin percent8.4%
Use the status as a demand-margin prompt before detailed board review.
The margin is below the target, so source values and board assumptions should be checked before the record is reused.
- The target margin is user-entered.
- Future allowance uses the same current basis.
- The page does not decide board suitability.
Small distribution board
A distribution board compares present demand with a small future allowance.
- Board reference
- DB-2
- Switchboard rating
- 160 A
- Target margin
- 15%
- Planned demand110 A
- Remaining margin50 A
- Margin percent31.25%
Use the status as a demand-margin prompt before detailed board review.
The margin stays above the entered target and can be compared with spare capacity and supply capacity records.
- Demand is current-based.
- The rating value is a comparison input.
- Switchboard documentation remains the source record.