Metered history
Twelve months of kWh, plus interval demand data for commercial sites. Estimates end where metering begins.
Methodology
How PanelCalc calculates.
Explicit-input models with visible formulas, dated baselines, machine-checked test cases, and a stated verification boundary. Screening-grade arithmetic for electrical work, not revenue metering.
The principle
Every result must be reproducible from the inputs on the page.
Each calculator is a fixed formula over labeled inputs. There are no hidden scores, no black-box adjustments, and no location lookups: the numbers you type, plus the stated defaults, fully determine the outputs. Every calculator page shows its formula, and every calculator ships with automated test cases that fixed inputs must reproduce before publication.
Units and conventions
One consistent system across all forty tools.
Power vs energy
kW measures rate of use; kWh measures accumulated use. Panel feeders are sized from current (A) and apparent power (kVA); energy (kWh) and its cost only enter the waste-heat and payback tools. Demand charges price peak kW over the utility interval (usually 15 minutes).
Money handling
Money enters only where a decision has a price: PF penalties (USD per kW-month), capacitor cost (USD per kVAR), wasted energy (USD per kWh), and equipment hints. Displayed money rounds to cents; intermediate values keep full precision so chained steps do not drift.
Duty cycle
Intermittent and simultaneous loads are modeled with explicit factors, never buried constants: simultaneity (%), inrush allowance (%), demand factor (%), and growth headroom (%). Each stays editable and labeled on the page, so a reviewer can see exactly what diversity was assumed.
Precision statement
Outputs are screening-grade: good enough to rank options, size a first pass, or check a quote. They are not revenue-grade metering and do not replace interval data, load studies, or short-circuit analysis.
Method by category
What each tool family models, and what it assumes.
Load and power
Single and three-phase relations (P = sqrt(3) x V x I x PF) at the entered voltage and power factor. Load summaries apply a demand factor, then size feeders at 125 percent of continuous current.
Wire and voltage drop
Drop follows 2 x K x I x L / cmil for single-phase and DC, sqrt(3) x K x I x L / cmil for three-phase. The length solver inverts the same relation against the allowed-percent budget. Copper K = 12.9, aluminum K = 21.2.
Motors and protection
Motor FLA derives from HP, efficiency, and power factor, checked against NEC 430 tables. Branch conductors size at 125 percent of FLA; inverse-time protection references the 175 percent rule; overloads follow 115/125 percent; multi-motor feeders add 125 percent of the largest plus the rest.
24V control power
Every 24V load is budgeted in simultaneous-on watts with at least 25 percent headroom, then stepped to a standard supply size. Branch fuses cover branch current; the longest run is checked for drop against device dropout voltage.
Components and heat
Resistor dissipation, coil energy (1/2 L I²), and braking energy sum into enclosure watts. Natural dissipation near 5.5 W per m² per K offsets the total; a positive remainder means active cooling.
Lighting, backup, and raceway
LED drivers load to 80 percent; injection spacing follows the drop budget; batteries and UPS quote usable energy against the backed load. Raceway tools apply NEC Chapter 9 fill, 310 ampacity, and infinite-bus fault current.
Sources and baselines
Dated numbers, named sources, annual review.
Usage and rate averages
Nameplate figures (for example, motor FLA, transformer %Z, and PSU efficiency) come from equipment ratings and NEC tables and carry their source. A yearly site review checks defaults against the newest references.
Code references
Where practice is discussed, the National Electrical Code is cited as context for why a rule exists, never as installation instruction. The locally adopted code and the authority having jurisdiction always govern.
Equipment figures
Typical wattages, COP ranges, and lifespans are labeled as starting points. Nameplate data and manufacturer sheets replace them during verification.
Verification protocol
Replace these five before relying on any result.
Current tariff sheet
Rates, tiers, windows, fixed fees, demand charges, ratchets, and riders exactly as billed this month.
Nameplate facts
Actual wattage, voltage, efficiency ratings, and duty behavior of the installed equipment.
Site conditions
Shading, orientation, service capacity, and coincident loads that no generic model can see.
Qualified review
A licensed electrician, installer, or utility advisor confirms the conclusion before money is spent.
Rate baselines are dated starting points, not live utility feeds. Calculator results are screening outputs, not utility bills, quotes, permits, or guarantees.
Known limits
What these tools deliberately do not do.
No code compliance
Nothing here determines whether an installation meets code. Sizing, protection, wiring methods, and clearances are field decisions under the AHJ.
No coincident-peak modeling
Load tools sum connected or average loads. Which loads coincide in the same 15-minute interval requires metered data the tools do not have.
No forecasts
Escalation and degradation inputs project arithmetic, not the future. They show sensitivity to assumptions; they do not predict rates, weather, or performance.
No account data
Public baselines never describe your account. Two neighbors on different tariffs can have legitimately different bills for identical usage.