Calculator
Advanced Notes
How to use
- Enter voltage, available fault current, and clearing time.
- Set the working distance used during the task.
- Choose equipment environment and electrode configuration.
- Adjust gap, enclosure, grounding, and safety margin.
- Press Calculate to view boundary and energy results.
- Download CSV or PDF for your job package.
Formula used (simplified)
K is a calibration constant for typical low-voltage ranges. The distance exponent x is auto-selected from your equipment choices or set manually. For compliance work, use a full IEEE 1584 method and validated device times.
Example data table
| Scenario | V | Ibf (kA) | t (ms) | WD | Gap (mm) | Ewd (cal/cm²) | Boundary (mm) |
|---|---|---|---|---|---|---|---|
| LV Panelboard | 480 | 25 | 150 | 457 mm | 32 | 0.037 | 45.0 |
| MCC Bucket | 600 | 35 | 200 | 455 mm | 25 | 0.088 | 80.0 |
| Open Air Disconnect | 240 | 10 | 100 | 18 in | 18 | 0.005 | 29.8 |
Limitations and safety
- Results are estimates and may differ from formal methods.
- Do not use this alone to approve energized work.
- Use qualified engineers, tested device times, and labels.
- Always follow site rules, permits, and PPE program.
Arc flash boundary planning guide
1) What the boundary represents
The arc flash boundary is the distance where a person without arc-rated protection could receive a second-degree burn from a brief electrical arc. Many safety programs use 1.2 cal/cm² as the default boundary threshold. Inside this distance, energized work normally requires arc-rated PPE, face protection, and a documented work plan.
2) Inputs that drive the result
Three variables typically dominate the boundary: available fault current, clearing time, and working distance. Higher fault current can sustain a stronger arc, longer clearing time increases exposure, and shorter working distance concentrates more energy on the worker. In low-voltage construction settings, clearing times of 50–300 ms are common, but miscoordination can push times higher.
3) Working distance and task reality
Typical working distances include 18 in (457 mm) for panelboards and 24 in (610 mm) for some switchgear tasks. Use the distance that matches the hands and face position during the work, not the cabinet door. If the task forces you closer, the incident energy rises quickly because energy falls with distance using an exponent (often around 1.2–2.0).
4) Gap, enclosure, and configuration effects
Conductor gap and enclosure characteristics influence how an arc forms and how heat and pressure exit the equipment. For planning, a 25–32 mm gap is frequently used for low-voltage gear. Enclosed equipment can direct more energy outward compared to open air, and electrode configuration can shift energy toward the worker’s position.
5) Clearing time and protective devices
Always base time on the protective device that will actually clear the fault for the work location. For example, a downstream breaker may trip in 0.08 s, but if it fails, an upstream device could take 0.3–0.6 s or longer. This calculator supports conservative planning by allowing a safety margin that increases the final incident energy.
6) Interpreting incident energy
Incident energy is reported at the working distance in cal/cm². Many PPE programs group protection levels into practical bands (for example, <4, 4–8, 8–25, and 25–40 cal/cm²). Treat these bands as guidance only and confirm garment ratings, face shields, gloves, and hearing protection requirements with your site standard.
7) Jobsite use cases
On active construction sites, arc flash planning is often needed for temporary power, panel upgrades, motor control work, generator tie-ins, and troubleshooting. Use the calculator to quickly estimate a conservative boundary, then mark the floor, control access, and brief the crew. If the result is unusually high, consider de-energizing, adjusting protection settings, or improving coordination.
8) Reporting and documentation
The CSV export is useful for job packages and daily safety paperwork, while the PDF report is convenient for supervisors and permits. Save the inputs that match the field conditions: voltage, fault current source, device time, and the exact task distance. For final approval, use stamped engineering labels where required and follow your lockout and verification procedures.
FAQs
1) What threshold should I use for the boundary?
Many programs use 1.2 cal/cm² because it aligns with second-degree burn criteria. If your organization uses a different threshold, enter it here to match your policy.
2) Where do I find bolted fault current?
Use a short-circuit study, utility data, transformer information, or upstream protective device documentation. If unsure, choose a conservative value and confirm with an engineer.
3) How do I estimate clearing time?
Use time-current curves from device settings or coordination studies. Include the device that would clear a fault at the work location, not only the main breaker.
4) Why does working distance matter so much?
Energy decreases with distance using a power relationship. A small reduction in distance can create a large increase in incident energy, especially in enclosed equipment.
5) What is the distance exponent?
It is the factor that controls how fast energy drops as you move away. Auto mode selects a typical value based on environment; use custom only if you have validated data.
6) Can I use this for medium-voltage gear?
You can enter higher voltages, but results remain simplified estimates. Medium-voltage arc studies are more sensitive to configuration and require formal methods for compliance.
7) Is a high boundary always a reason to stop work?
It’s a warning sign to reassess controls. Consider de-energizing, improving protection settings, reducing exposure time, increasing distance, or changing the work method.