Inputs
- Primary voltage
- Control voltage
- Control load
Control Transformer Sizing
Stop recalculating transformer VA and fuse sizes every time the control load changes.
Change the load or voltage and the system updates transformer size, calculated currents, protection, and generated data automatically. LogiDraft applies rule-driven sizing so the schematic and generated data stay in sync.
Change control load or voltage and watch transformer size and fuse protection update instantly.
Primary Voltage240 or 480 V
Control Voltage24 or 120 V
Sizing RuleRequired VA = load x 1.25
Lookup OutputTransformer + fuse selection
Automatic transformer sizing and protection
This sizing result is generated directly from the same logic used in the workspace.
- At 50 VA load: 75 VA transformer, 1 A primary fuse, 5 A secondary fuse.
- At 500 VA load: 750 VA transformer, 5 A primary fuse, 50 A secondary fuse.
Change load or voltage and the sizing updates automatically.
Increasing load steps transformer size from 75 VA to 750 VA and scales fuse protection automatically.
Change inputs in the workspace and this result updates automatically.
These changes are reflected directly in structured output data.
| Control Load (VA) | Transformer (VA) | Primary Fuse (A) | Secondary Fuse (A) |
|---|---|---|---|
| 50 | 75 | 1 | 5 |
| 500 | 750 | 5 | 50 |
Geometry and data stay aligned because they are generated from the same logic.
Inputs and outputs
Control load and voltage resolve the transformer selection, calculated currents, and protection values together.
Outputs
- Transformer VA
- Primary and secondary currents
- Primary and secondary fuse sizing
Rule-driven sizing logic
The sizing logic follows standard electrical calculations, encoded directly in the model.
Calculation flow
- Calculate required VA as control load multiplied by 1.25.
- Select the next standard transformer size with lookup logic.
- Calculate primary current from transformer VA and primary voltage.
- Calculate secondary current from transformer VA and control voltage.
- Select primary and secondary fuse sizes from standard ratings.
Standard ratings
The example uses standard fuse sizes of 1, 2, 3, 5, 10, 15, 20, 30, and 50 A. Fuse protection is selected by rounding each calculated current up to the next available standard rating.
Because the calculations are encoded directly in the model, the transformer symbol and both fuse symbols stay aligned with the resolved values without extra manual checking.
Outputs
The resolved transformer produces usable engineering data that can be exported and kept aligned with the visible sizing result.
Required VA, transformer size, currents, and fuse values are available as generated data from the same evaluated model.
Exported data stays aligned with the schematic, so schedules and downstream checks can use the same resolved values.
Outputs50 VA load sample
CSV / JSON| Required VA | 62.5 |
|---|---|
| Transformer Size (VA) | 75 |
| Primary Current (A) | 0.31 |
| Secondary Current (A) | 3.13 |
| Primary Fuse (A) | 1 |
| Secondary Fuse (A) | 5 |
Manual sizing versus LogiDraft
Transformer sizing is repetitive work. Encoding it once keeps the calculation, the schematic, and the generated data aligned.
Calculate, round, then redraw
- Apply the safety factor by hand.
- Pick the next standard transformer size manually.
- Recalculate currents for every voltage change.
- Choose standard fuse ratings separately from the schematic.
One rule set drives the result
- The sizing factor is applied consistently every time.
- The transformer VA comes from the defined standard-size lookup.
- Current and fuse calculations stay tied to the same resolved values.
- The drawing and the structured output remain correct together.
Use this example
How this works
Open the example and change inputs to see the system update
Open this and change one value - you'll immediately see how the system works.
Open this example and:
- Change control load or voltage
- Watch transformer size, currents, and fuse sizing update automatically
Related parametric panel workflows
Control transformer sizing is a focused example of inputs, lookup tables, drawing updates, and output data staying connected.
Parametric electrical CAD
See how inputs, formulas, lookup tables, reusable definitions, drawings, and outputs fit together as a category.
Read the parametric CAD guideControl panel design software
Learn how control transformer logic fits into broader control panel workflows with schematic and BOM coordination.
Read the panel workflow guideRelated pages
Help
How to use lookup tables for sizing logic.
Docs
How lookup-driven logic resolves behavior.
Example
Another practical lookup-driven sizing system.
Reference
Exact lookup function syntax.