Switchboard demand margin calculator
Compare Australian switchboard rating, calculated demand and future allowance to show remaining demand margin.
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.