Circuit Load Calculator

1. Select system type and phase, then enter circuit voltage.
2. Enter power factor for AC loads and a demand factor.
3. Set the continuous portion; the tool applies a 125% uplift.
4. Add existing and future allowances to avoid undersizing.
5. Enter conductor length, material, and voltage drop target.
6. Fill load items and press Calculate to see results.
7. Use the exports to attach results to your job file.

Practical Notes for Circuit Load Planning

1) Why circuit load planning matters

In construction, branch circuits are often revised late, when finishes and equipment lists change. A structured load estimate reduces nuisance trips, overheating, and rework. This calculator totals connected watts, applies realistic diversity, and converts the result into design current for quick sizing decisions.

2) Connected load versus demanded load

Connected load is the sum of every listed device (qty × watts) plus allowances. Demand factor recognizes that not all loads run simultaneously. For example, 5,500 W of tools at a 0.80 demand factor becomes 4,400 W equivalent before other adjustments.

3) Continuous loads and the 125% uplift

Many standards treat continuous loads as those expected to run for extended periods. This tool applies a 125% multiplier to the continuous portion only. If a circuit has 4,000 VA after demand and 60% is continuous, the uplift adds 0.25 × 2,400 = 600 VA, producing 4,600 VA before margin.

4) Power factor and apparent power

For AC, current is driven by apparent power (VA). Loads with PF below 1.0 draw more current for the same watts. A 2,800 W lighting circuit at PF 0.95 equals about 2,947 VA. At 230 V single-phase, that is roughly 12.8 A before demand and continuous effects.

5) Single-phase and three-phase current

Single-phase current uses I = VA / V. Three-phase current uses I = VA / (√3 × V). With 12,000 VA on a 400 V three-phase system, current is about 17.3 A. These distinctions help prevent undersizing when a project mixes panel types.

6) Voltage drop as a planning check

Long runs can cause dimming, motor stress, and control faults. Many teams target 3% for branch circuits. The calculator estimates voltage drop using circular-mil method and one-way length. If drop exceeds the target, the suggested conductor size steps up until it meets the limit.

7) Breaker selection and engineering margin

After the design current is calculated, the tool recommends the next common breaker size. Adding a modest margin (often 5–15%) can accommodate measurement uncertainty, minor additions, and temperature effects. Always confirm local requirements for derating, bundling, and termination ratings.

8) Documentation for teams and inspections

Field coordination improves when calculations are traceable. Use the itemized table to show assumptions, then export CSV or PDF for submittals, RFIs, or punch-list closeout. Clear records help electricians, engineers, and inspectors align on what the circuit was designed to serve.

FAQs

1) What demand factor should I use?

Use 1.00 for worst-case simultaneous use. Choose lower values for diversified loads, like general receptacles or mixed tools. If unsure, start near 0.90 and adjust based on real operating patterns.

2) What counts as a continuous load here?

Continuous loads are those expected to run for long durations, such as lighting, signage, or ventilation. Enter the estimated percentage; the tool applies a 125% factor to that portion only.

3) Why does power factor change the result?

For AC circuits, current depends on apparent power (VA), not just watts. A lower PF increases VA for the same wattage, which raises calculated current and may require a larger breaker and conductor.

4) Which voltage should I enter for three-phase?

Enter the line-to-line system voltage used by your equipment and panel, such as 400 V or 480 V. The tool uses √3 in the current equation to convert VA into line current.

5) What is a good voltage drop target?

A 3% target is commonly used for branch circuits, while longer feeders may allow 5% overall when combined. Choose a stricter target for sensitive electronics, lighting quality, or motor starting performance.

6) Can I rely on the wire size suggestion?

Treat it as a planning estimate. Real installations must consider insulation temperature rating, ambient temperature, conduit fill, grouping, termination limits, and local code tables. Verify final selection with your project’s governing standard.

7) Why is the recommended breaker higher than calculated amps?

Breakers come in standard sizes, and continuous loads often require extra capacity. The tool also allows an engineering margin. The recommendation is the next standard size above the calculated design current.