WorksheetCode-sensitiveLast reviewed May 17, 2026
Electrical reference chart
Transformer Nameplate Secondary Worksheet Chart
Use this worksheet after the transformer calculator result to record nameplate kVA, primary and secondary voltage, phase, impedance, taps, secondary current, grounding point, protection note, and manufacturer data.
Quick reference table
A transformer nameplate secondary worksheet keeps equipment data and load-side current together. It is distinct from transformer sizing because it records the selected or existing transformer before secondary conductor, protection, and fault-current review.
Transformer nameplate record
| Nameplate field | Record on worksheet | Downstream use |
|---|---|---|
| Rating | kVA, phase, frequency, temperature rise | Defines load and duty basis |
| Voltage | Primary voltage, secondary voltage, taps | Separates feeder side and load side |
| Current | Primary current, secondary current | Feeds conductor and protection review |
| Impedance | Percent Z, X/R if available | Feeds available fault-current review |
| Installation | Enclosure, ventilation, grounding, location | Keeps field constraints visible |
Secondary handoff checklist
| Handoff | Keep visible | Do not collapse into |
|---|---|---|
| Sizing chart | Load kVA, spare capacity, standard rating | Nameplate current only |
| Impedance chart | Percent Z, available fault current, source note | kVA selection only |
| Short-circuit review | Secondary current and impedance basis | Breaker shortcut |
| Service or feeder review | Secondary voltage, grounding, conductor path | Unlabeled transformer amps |
Formula basis
Three-phase secondary current = transformer kVA x 1000 / (1.732 x secondary volts). Single-phase current = kVA x 1000 / secondary volts.
- Transformer kVA comes from the nameplate or selected equipment rating.
- Secondary volts are the load-side line voltage used for the current calculation.
- Phase changes the current formula and must be labeled.
- Impedance and taps do not replace the current formula, but they affect fault-current and voltage review.
Worked examples
Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.
- This worksheet records transformer nameplate and secondary-current context; it does not select conductors, breakers, or listed equipment by itself.
- Final installation depends on manufacturer instructions, equipment listing, adopted NEC edition, grounding method, available fault current, local amendments, and AHJ review.
Code and standard notes. Planning limits that should be checked before final equipment selection.
- Use this chart as a field record; verify adopted NEC transformer, grounding, overcurrent, conductor, ventilation, and working-clearance requirements with manufacturer instructions, equipment listing, local amendments, AHJ expectations, and qualified-person review.
How to use this chart
Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.
- Record transformer identityWrite manufacturer, model, kVA, voltage, phase, impedance, taps, and location.
- Record calculated valuesWrite primary current, secondary current, available fault-current basis, and load margin.
- Record review controlsList grounding method, protection basis, manufacturer manual, AHJ note, and reviewer.
Common mistakes to avoid. Review these before turning chart current into an equipment decision.
- Using secondary current on the primary side or primary current on the secondary side.
- Recording kVA without voltage, phase, impedance, tap, and grounding context.
- Treating nameplate current as a completed conductor or breaker selection.
Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.
Why create this if a transformer sizing chart already exists?
The sizing chart screens kVA. This worksheet records the actual nameplate and secondary-side data needed after a transformer is selected or surveyed.
Why keep primary and secondary current separate?
Primary and secondary voltages are different on most transformers, so the currents are different and feed different conductor and protection decisions.
Related calculators
- Transformer CalculatorScreen transformer kVA, turns ratio, full-load current, operating-point losses, and secondary-terminal fault current from basic nameplate inputs.
- Transformer Impedance CalculatorCalculate transformer percent impedance (%Z), X/R ratio, short circuit current, and impedance components. Essential for short circuit studies and protective device coordination.
- Short Circuit Current CalculatorEstimate available fault current from transformer impedance, feeder impedance, or known source impedance.
- Electrical Service Size CalculatorScreen dwelling-service ampacity from floor area, major electric loads, and a dwelling-style demand method with optional existing-service comparison.
Related charts
- Transformer Sizing ChartEstimate transformer kVA from load current, voltage, and phase, then document primary and secondary current, impedance, inrush, ventilation, and protection notes.
- Transformer Impedance ChartPlan transformer impedance checks for available fault current, voltage regulation, primary/secondary current, equipment rating, and coordination context.
- Short Circuit Current ChartPlan short-circuit current checks from utility data, transformer kVA and impedance, voltage, conductor path, motor contribution, and equipment SCCR/AIC.
- kVA to Amps ChartUse the kVA to amps chart with voltage, phase, and equipment role, then open the transformer calculator when the current feeds a project review.