About PanelCalc — Power & Control Panel Calculators

What PanelCalc is

PanelCalc (panelcalculators.com) is a system-sizing reference for low-voltage power and control panels: forty calculators that answer three questions in order — how much power, what wire, what protection. Every tool shows its inputs, its formula, and its outputs on the page, so any result can be checked by hand, against a spreadsheet, or against the cited NEC article.

Who this site is for

The primary reader is the panel builder laying out a UL 508A / IEC 61439 style control panel: sizing the feeder, the 24 V control power, the branch protection, and the enclosure cooling. Around that reader are three more:

• Controls engineers budgeting PLC racks, HMI, sensors, and solenoid valves into a 24 V supply with defensible headroom and fused branches.
• Electricians verifying feeder current, voltage drop on long runs, breaker sizes for continuous loads, and motor branch-circuit compliance before inspection.
• Facility and maintenance teams cross-checking a contractor quote — feeder kVA, fault-current AIC, enclosure heat — against their own numbers.

Why it exists

Panel work runs on numbers that are easy to get slightly wrong: feeder current for a motor group under NEC 430.24, voltage drop on a 24 V run that resets field devices, the breaker size for a continuous load under NEC 240, or whether an enclosure needs a fan or an air conditioner. Small errors compound into tripped breakers, failed inspections, nuisance faults, or cooked components. This site exists to make those numbers checkable in minutes, with every assumption visible on the page.

The seven tool families

• Load and power (5 tools): single and three-phase power, kW/kVA/PF conversion, panel load summaries with demand factor, and power-factor correction with payback.
• Wire and voltage drop (5 tools): NEC Chapter 9 R+X drop for DC, single and three-phase runs, a max-length solver, and resistance/loss with annual waste cost.
• Motors and protection (5 tools): FLA estimation cross-checked against NEC Table 430.250, branch-circuit conductors, OCPD selection per NEC 240.6, overload relay settings, and multi-motor feeder summaries.
• 24 V control power (3 tools): PLC-panel power budgets with simultaneity and inrush margins, fused branch planning with drop checks, and PSU headroom/efficiency analysis.
• Components and heat (3 tools): resistor dissipation with 2x rating guidance, coil and braking energy, and enclosure heat-loss balance with ventilation hints.
• Lighting and backup (4 tools): LED driver sizing at the 80% rule, injection spacing, battery runtime by chemistry, and UPS load budgets.
• Raceway and equipment (5 tools): conduit fill per NEC Chapter 9, ampacity with bundling and ambient derating, fault current with AIC verdicts, transformer FLA both sides, and box fill per NEC 314.16.

How content is produced and reviewed

Each calculator ships with machine-checked test cases: fixed inputs must reproduce fixed outputs through the actual calculation engine before the tool is published, and the engine re-verifies them on every release. Conductor properties come from an embedded NEC Chapter 9 Table 8 dataset; motor table values from NEC Table 430.250; standard breaker sizes from NEC 240.6 — each dataset carries its standard, edition, and source URL. A yearly site review checks defaults against the newest references. When a reader reports an error through Contact, the page is corrected and the correction is noted.

Editorial independence

Calculator defaults and guide examples are editorial choices, not endorsements. The site does not accept payment to favor equipment, installers, or rate plans in its tools or content. If that ever changes for a specific page, the relationship will be stated on that page.

What this site is not

PanelCalc is a planning and reference tool. It is not a substitute for the National Electrical Code as adopted and amended locally, the authority having jurisdiction, manufacturer instructions, or the judgment of a licensed professional on site. A calculator output is not an approval, a permit, a quote, or a guarantee of performance. Read the Disclosure before relying on any result.

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