Example data table
| Typical outdoor item | Approx. watts | Notes |
|---|---|---|
| LED path lights (10) | 30–80 W | Low surge; often runs for hours. |
| Pond pump | 150–500 W | Motor start surge can be 3–6×. |
| Pressure washer | 1200–2000 W | High load; avoid sharing with other loads. |
| Electric trimmer | 300–800 W | Surge varies with motor type. |
Values are typical ranges for planning, not equipment labels.
Formula used
- Running current: I = P ÷ (V × PF)
- Running power: P = I × V × PF
- Demand adjustment: Demand = Running × (Factor ÷ 100)
- Continuous limit: Allowable = Breaker × 0.80 (or 1.00)
- Start-up peak estimate: running total plus largest motor start uplift.
- Voltage drop: Vdrop = I × R, with loop resistance for out-and-back wire.
How to use this calculator
- Select your supply voltage and breaker rating.
- Choose the continuous rule and a demand factor.
- Enter each outdoor device with watts or amps.
- Set power factor for motors, usually 0.8–0.95.
- Add surge multipliers for pumps and motor tools.
- Optionally enable voltage drop with wire details.
- Press Calculate and review demand, peak, and headroom.
- Export CSV or PDF for planning and recordkeeping.
Load inventory for outdoor devices
Start by listing every connected item: path lights, timers, fountains, chargers, and seasonal décor. Enter values in watts when labels show power, or in amps when only current is known. Use realistic quantities and keep names specific, because the export report mirrors your table for later review. For motorized items, set power factor between 0.80 and 0.95 to avoid understating current.
Demand factor and continuous planning
Outdoor equipment often runs intermittently, so the demand factor lets you model diversity. Set 100% when everything can operate together, then try 70–90% for mixed-use areas. For loads that can run for hours, apply the 80% continuous rule to keep operating current below the breaker’s long-duration limit. When unsure, confirm common breaker sizes from the panel label before planning additions.
Surge behavior for pumps and motors
Motors draw higher current at start. Add a surge multiplier to represent this brief inrush, typically 3–6 for pond pumps and pressure-boost units, and 2–3 for small tools. The calculator estimates a combined peak by adding the largest motor uplift to the running total, highlighting trip risk. For electronic supplies, keep surge at 1.0 because inrush is usually minimal.
Voltage drop checks for long runs
Long cable routes to a shed or pergola can reduce voltage at the load. Enable voltage drop, choose conductor material and gauge, and enter one-way length. The tool uses loop resistance and Vdrop = I×R, then flags higher percentages so you can consider thicker wire or shorter routing. A practical target is under 3% drop for consistent pump starts and bright LEDs.
Documenting results for garden upgrades
After calculating, save the CSV for spreadsheets or download a PDF for site folders and client handoffs. Use the headroom figure to decide whether new fixtures fit the circuit, and repeat scenarios with different demand and surge assumptions. Attach season, runtime, and maintenance notes beside the saved report for clarity. For later reference.
FAQs
1) What does the demand factor change?
It scales the running totals to reflect diversity. Use 100% when all devices may run together. Use a lower value when loads are scheduled or unlikely to overlap, and compare results across scenarios.
2) When should I use the 80% continuous rule?
Use it for loads that can run for hours, such as landscape lighting or circulation pumps. It sets a conservative continuous limit so the planned current stays comfortably below the breaker rating.
3) Why is power factor included?
Power factor affects how watts translate to amps for motorized equipment. If you enter watts for a pump, a lower power factor increases calculated current, helping avoid an optimistic estimate that could overload a circuit.
4) How do I choose a surge multiplier?
Set 1.0 for resistive loads and most electronic supplies. Use 2–3 for small motor tools, and 3–6 for pumps or compressor-like loads. If unsure, start higher and review peak warnings.
5) What voltage drop percentage is acceptable?
Many planners aim for under 3% on long runs, especially for motors and LED lighting. Higher drop can cause dim lights, slow starts, and nuisance trips. Consider thicker conductors or shorter routing.
6) Do the exports include my load table?
Yes. The CSV includes each row and summary metrics, while the PDF includes a summary table plus the detailed load list. Run a calculation first so the export contains updated results.
Safety note
This tool is for planning and estimating only. Outdoor circuits should follow local electrical rules, use appropriate protection devices, and be installed by qualified people when required.