Calculator Inputs
Formula used
- Demand load: Continuous kW × factor + selected demand loads.
- Seasonal load: Larger of heating and cooling load.
- Motor allowance: Total motor kW + largest motor extra percent.
- Apparent power: kVA = design kW ÷ power factor.
- Three phase current: A = kVA × 1000 ÷ √3 × V.
- Panel selection: next standard panel above required current.
- Neutral current: vector sum of unbalanced single phase currents.
How to use this calculator
- Enter the three phase line voltage and power factor.
- Add continuous, noncontinuous, lighting, and receptacle loads.
- Enter equipment, seasonal, and motor loads.
- Set demand factors based on project assumptions.
- Add single phase loads by phase for balance review.
- Press calculate to see the result above the form.
- Use the export buttons for records and reporting.
Example Data Table
| Input | Example value | Purpose |
|---|---|---|
| Line voltage | 415 V | Find three phase current. |
| Power factor | 0.95 | Convert kW to kVA. |
| Continuous load | 18 kW | Apply continuous factor. |
| Equipment load | 20 kW | Apply equipment demand. |
| Spare capacity | 20% | Reserve future panel capacity. |
Three Phase Panel Planning
Three phase panel sizing starts with a reliable load list. Each load must be classified before calculation. Continuous loads need a higher design allowance. Noncontinuous loads usually use their normal demand. Motors need special attention. The largest motor often needs an extra allowance. Heating and cooling loads are compared carefully. Usually the larger seasonal load is used.
Why Panel Size Matters
A panel that is too small overheats easily. It may nuisance trip during normal operation. A panel that is too large can waste budget. It may also hide poor load planning. Good sizing protects feeders, breakers, and equipment. It also leaves room for future circuits. The result should guide early estimating. Final selection still needs local code review.
Demand And Diversity
Connected load is not always the real design load. Many circuits do not run together. Demand factors reduce selected load groups. Receptacles, lighting, equipment, and tools may differ. This calculator lets you set each factor. Use conservative values when usage is uncertain. Construction sites often change quickly. Spare capacity helps absorb those changes.
Balancing The Phases
Balanced panels run cooler and cleaner. Uneven single phase loads stress one phase. The calculator compares phase A, phase B, and phase C. It estimates maximum phase current. It also estimates neutral current for wye systems. High imbalance should be corrected early. Move branch circuits between phases when practical. Recheck the panel after every major change.
Practical Construction Use
Use this tool during takeoff, tendering, and coordination. Enter realistic equipment loads from drawings. Add temporary construction loads when needed. Include cranes, pumps, heaters, welders, and offices. Use nameplate data when available. Do not guess motor values. Check voltage and power factor before sizing. A wrong voltage can change current sharply. Record assumptions beside each result. Keep a copy with project notes. Update loads when drawings change. Review spare capacity before adding tenants or major machines. Always document changes.
Engineering Notes
The tool estimates apparent power and line current. It uses the square root of three factor. It then selects the next common panel rating. Available sizes are practical estimating values. Actual products vary by manufacturer. Short circuit rating is not calculated here. Grounding and feeder sizing need separate checks. Final sizing should follow approved plans and field conditions.
FAQs
What is a three phase panel load calculation?
It estimates total electrical demand on a three phase panel. It converts load power into line current. It then supports panel size selection.
Why is power factor important?
Power factor changes apparent power. Lower power factor increases current. That can require a larger panel and feeder.
Should continuous loads be multiplied by 125%?
Many design methods use 125% for continuous loads. Always confirm the rule with the local electrical code and project engineer.
How does the calculator choose panel size?
It finds calculated current with spare capacity. Then it selects the next common standard panel ampere rating.
What is phase imbalance?
Phase imbalance compares phase currents against their average. High imbalance can heat conductors and reduce system performance.
Does this replace engineering design?
No. It is an estimating tool. A licensed professional should verify final panel, feeder, breaker, and protection choices.
Why use the larger heating or cooling load?
Heating and cooling usually do not run together at full load. Using the larger value avoids unnecessary double counting.
Can I include temporary construction loads?
Yes. Add cranes, welders, pumps, heaters, offices, or site tools under suitable load categories.
What spare capacity should I use?
Many projects use ten to twenty five percent. Higher spare capacity helps future changes but increases panel size.
Why is neutral current estimated?
Single phase loads may not balance across phases. The neutral estimate helps review wye panel loading.
Can I export the result?
Yes. Use the CSV button for spreadsheet records. Use the PDF button to print or save the visible result.