Electrical

236 calculators. Every one runs in your browser. Free, no account.

Search all 1,940 calculators

Tools in this group

Ohm's Law - Compute V, I, R, or P from any two known values.
Wire Ampacity - Ampacity by gauge, conductor material, insulation rating, ambient.
AWG Conductor Geometry (Diameter, Circular Mils, mm^2) - The bare-conductor size behind a gauge number, from the AWG definition.
Multiwire Branch Circuit (3-Wire) Voltage Drop - Voltage drop on a 120/240 V multiwire branch circuit, where two hot legs share one neutral.
Voltage Drop - Single-phase or three-phase voltage drop over length.
Conduit Fill - Percent fill by conduit type and conductor count.
Box Fill - Cubic-inch fill by box volume and conductor count.
Breaker Sizing - Continuous-load 125 percent rule.
Motor Full Load Amps - Typical FLA by horsepower, voltage, and phase.
Transformer Sizing - Required kVA from load and voltages.
Three-Phase Power - kW, kVA, and kVAR from line values and power factor.
Conductor Resistance at Temperature - Resistance of copper or aluminum at temperature.
EGC for Parallel Raceways (NEC 250.122(F)) - The equipment grounding conductor for each raceway of a paralleled feeder, per NEC 250.122(F).
Equipment Grounding Conductor Sizing - Minimum EGC size from overcurrent device rating.
Service Load Calculation (Residential) - Standard demand factors over lighting, appliances, range, dryer, HVAC; output minimum service ampacity.
Generator Sizing - Continuous and surge wattage from running totals and the largest motor's starting draw.
Solar PV String Sizing - Cold-Voc max series and warm-Vmp min series for an inverter MPPT window.
Battery Runtime - Hours of runtime from Ah, voltage, depth of discharge, and load (optional Peukert).
DC Ammeter Shunt Sizing - Sizing and reading a DC current-measuring shunt.
Voltage Imbalance - Three-phase percent imbalance and motor derate factor.
GFCI / AFCI Requirements Reference - Plain-English summary of GFCI and AFCI requirements by occupancy area.
Lighting Power Density - Target watts from area and occupancy class using public engineering benchmarks.
Conductor Pulling Tension - Capstan-equation pulling tension and sidewall pressure across bends.
Cable Reel Capacity / Length on Reel - How many feet of a given cable fit on a reel (or how much is left on a partial reel).
Cable-Pulling Lubricant Quantity - Estimates the pulling lubricant a conduit run takes, so the crew does not run short mid-pull.
Branch-Circuit Conductor Footage Takeoff - Takes off the branch-circuit wire to order and how many rolls.
Max Microinverters per AC Branch Circuit (NEC 705.60) - The most microinverters or AC modules on one AC branch circuit.
Arc-Welder Branch-Circuit Conductor and OCPD (NEC 630.11) - Sizes an arc-welder branch circuit off the nameplate, not the running current.
Resistance / Spot-Welder Branch-Circuit Conductor and OCPD (NEC 630.31) - Sizes a resistance (spot / seam / projection) welder branch circuit.
Battery-to-Inverter DC Conductor and OCPD (NEC 690.9 / 706) - Sizes the DC conductor and fuse between a battery bank and an off-grid or ESS inverter.
Inverter AC Output Circuit Conductor and OCPD (NEC 690.8(B)) - Sizes the conductors and overcurrent device from a PV/ESS inverter to the point of connection.
Wenner 4-Pin Soil Resistivity - Apparent soil resistivity from a Wenner 4-pin (four-electrode, equal-spacing) earth test.
Cable Bend Radius Minimum - Minimum inside bend radius as a multiple of cable OD per manufacturer bulletins.
Power Factor Correction Capacitor - Required kVAR and capacitance to raise existing PF to target.
Phase Balance Across Panels - Per-phase totals, imbalance percent, and a greedy swap list to rebalance.
Branch Voltage Drop With Multiple Loads - Cumulative voltage at each tap along a run with multiple loads.
Low-Voltage DC Drop - DC voltage drop and percent at 12 / 24 / 48 V with application-tolerance flags.
PoE Budget and Run Distance - Power available at PD over Cat5e/6/6A given PoE class and run length.
Transformer kVA Sizing and FLA - Total connected kVA + ANSI/IEEE step-series recommendation + primary / secondary FLA.
Short-Circuit Current at Panel (Point-to-Point) - I_sca at transformer secondary, M-factor, and let-through fault current via the Bussmann point-to-point method.
Generator Sizing for Motor Starting - Required generator kW / kVA from running load and motor-starting kVA at the 30% voltage-dip criterion.
Service Entrance Demand Load (Standard Method) - NEC Article 220 Standard Method demand-factor walk; recommended service ampacity from the standard ladder.
Panel Loading and Phase Rebalance - Per-phase totals, percent imbalance, and a swap suggestion to minimize neutral current.
Arc-Flash Incident-Energy Screen (Lee 1982) - Simplified pre-IEEE-1584 incident-energy estimate and PPE band.
Motor Branch-Circuit from Nameplate - Compute full-load current from HP / V / eta / PF; flag the design value as the larger of computed vs nameplate.
Grounding Electrode Resistance (Dwight / IEEE 142) - Driven rod / ring / plate / Ufer resistance to earth from soil resistivity.
PV Interconnection 120% Busbar Rule - Load-side PV breaker check against the NEC 705.12 busbar limit (120% opposite-end allowance / 100% otherwise).
Off-Grid Battery Bank Sizing - Required nameplate capacity (Wh and Ah) from daily load, days of autonomy, depth-of-discharge, and round-trip efficiency.
Voltage Drop With Reactance - Single- or three-phase voltage drop using NEC Chapter 9 Table 9 R and X per 1000 ft and the load power factor.
Power Triangle Solver (kW / kVA / kVAR / PF) - Solve the full AC power triangle from any two of real power, apparent power, reactive power, power factor.
EV Charger Continuous Load and Panel Impact - Continuous-load circuit ampacity (125% per NEC 625.41/625.42), breaker, conductor, new panel total.
EV Charge Time (AC Level 2) - How long an AC Level 2 EV charge takes: energy = capacity x (target - start).
Battery Bank Series/Parallel Configuration - The series/parallel wiring of a battery bank.
Bifacial PV Rear-Side Gain - The extra output a bifacial module makes from light on its BACK side.
EV Range Added per Hour of Charging - How many miles of driving range an hour of charging adds.
EV Charge Cost at the Meter - What one EV charge costs on the utility meter, not the dashboard: you pay for kWh at the meter, not at the battery.
EV DC Fast-Charge Time (CC-CV Taper) - Why '80% in 20 minutes' is only the first leg.
PV Equipment Grounding Conductor (NEC 690.45) - The PV-specific equipment grounding conductor per NEC 690.45.
Conductor Ambient and Fill Ampacity Adjustment - Ampacity after the NEC ambient-temperature and conductor-fill correction factors.
Service Load Calculation (NEC 220.82 Optional Method) - Optional-method dwelling demand (first 10 kVA at 100% + remainder at 40% + larger HVAC).
Lux / Footcandle Converter and Lumen Method - Exact lux <-> footcandle conversion and the lumen-method average maintained illuminance from luminaire lumens.
Parallel Conductor Ampacity - Total ampacity of paralleled conductor sets after the NEC fill and ambient adjustments.
Three-Phase Neutral Current - Unbalanced neutral current from the phasor sum of three 120-degree-displaced phase currents.
Motor Starting Voltage Dip - Voltage dip during motor start from locked-rotor current and conductor length.
Conduit Offset Bend - Mark spacing, shrink, and multiplier for a two-bend conduit offset at a chosen angle.
Conduit Saddle Bend - Three-point and four-point saddle marks, bend angles, and shrink to clear an obstruction.
Conduit 90 Stub and Back-to-Back - Stub-up deduct mark, back-to-back spacing, and segmented-90 shot count.
Feeder Sizing for Multiple Motors - Feeder conductor (NEC 430.24) and feeder overcurrent device (NEC 430.62) for several motors on one feeder.
Transformer Conductor and Overcurrent Protection - Transformer primary and secondary FLA with the NEC 450.3(B) overcurrent maxima.
Fiber Optic Loss Budget - Total fiber link loss and the margin against the application's maximum channel loss.
Free-Space Path Loss (Wireless Bridge) - Free-space path loss on a point-to-point wireless bridge.
Fresnel Zone Radius and 60% Clearance - The line-of-sight clearance a point-to-point wireless link needs: the Fresnel zone radius and the 60% rule.
Wireless Link Budget (EIRP and Fade Margin) - The full point-to-point RF link budget: EIRP, received power, and fade margin.
Fiber Max Length for a Loss Budget - The longest fiber run that still passes the channel loss budget.
Cable Tray Fill - Cable-tray fill against the NEC 392.22 sum-of-diameters or cross-sectional-area allowance, with a pass/fail.
IP Camera / NVR Storage and Bandwidth - Total storage, aggregate switch bandwidth, and per-camera daily storage from bitrate, recording schedule, and retention.
CCTV Retention Days from Disk Capacity - How many days of footage a given NVR disk holds, from camera count, bitrate.
70-Volt Distributed Speaker Line - Tap-wattage budget, reflected line impedance (Z = V^2/P), remaining taps.
Fire-Alarm / Security Standby Battery - Required battery amp-hours from standby and alarm loads times the aging/derate factor.
Standby Battery Runtime from Capacity - The standby (supervisory) hours an installed fire-alarm or security battery supports before the alarm load.
Coaxial Cable Attenuation - Total coax attenuation over a run, end-of-run signal level.
Camera Lens FOV and Pixel Density (DORI) - The horizontal field of view, scene width, and pixel density of a surveillance camera.
Camera Max Distance for a Pixel Density (DORI) - The farthest distance a camera still meets a target pixel density (a DORI task).
Ceiling Speaker Coverage and Spacing - The coverage diameter, spacing, and speaker count for a distributed ceiling system.
Ceiling Speaker Coverage Angle for a Target Spacing - The coverage angle a target coverage diameter (or on-center spacing) needs at a mounting drop.
Structured Cabling Channel Length (TIA-568) - Whether a twisted-pair horizontal channel is within the TIA-568 limits.
Low-Voltage Cable Footage and Box Count - Cable footage and pull-box count for a drop count.
PVC Raceway Expansion Fitting - PVC conduit thermal length change, whether an expansion fitting is required (>= 0.25 in).
PV Racking Rail, Clamp, and Splice Takeoff - The rail, clamps, and splices a rooftop PV array needs.
PV Flat-Roof Ballast Weight and Roof PSF Screen - Dead-load screen for a ballasted flat-roof PV array.
J-Hook / Bridle-Ring Count and Bundle Weight - J-hooks / bridle rings for a cable pathway and the bundle weight each carries.
Access-Control Power Supply and Standby Battery - Sizes the power supply and standby battery for an access-control door system.
Fire-Alarm NAC Circuit Voltage Drop (End-of-Line) - Checks that a fire-alarm notification-appliance circuit (NAC) still drives its horns and strobes at the far end.
4-20 mA Current-Loop Signal Scaling - The engineering value a 4-20 mA instrument signal represents, read off a loop meter.
DP (Square-Root) Flow Transmitter 4-20 mA Scaling - The flow a DP transmitter's 4-20 mA signal represents: square-root, not linear.
RTD (Pt100 / Pt1000) Resistance to Temperature - The temperature a platinum RTD's measured resistance corresponds to.
Pulse Flowmeter K-Factor (Frequency to Flow) - Flow rate from a pulse meter's output frequency and its stamped K-factor.
Loop-Powered (2-Wire) 4-20 mA Transmitter Voltage Budget - Whether a loop-powered 2-wire 4-20 mA transmitter has enough voltage to operate.
NTC Thermistor Resistance to Temperature (Beta Equation) - The temperature an NTC thermistor's measured resistance corresponds to.
NTC Thermistor Steinhart-Hart Equation (3-Constant) - The accurate 3-constant temperature form the beta equation approximates.
PID Loop Tuning (Ziegler-Nichols Closed-Loop) - Starting PID gains from the Ziegler-Nichols closed-loop (ultimate-sensitivity) method.
Hydrostatic DP Level Transmitter (Head to Level) - The liquid level a hydrostatic (differential-pressure) level transmitter reports from the head it measures.
Motor Running Overload Protection (NEC 430.32) - Running overload protection for a motor, sized on the nameplate FLA.
Motor Locked-Rotor Current from Code Letter (NEC 430.7(B)) - Starting current from the nameplate code letter, not '6x FLA'.
Max Motor HP for a Starting-Current Budget (NEC 430.7(B)) - The largest motor a starting-current budget can actually start.
Motor Short-Circuit Contribution (First Cycle) - The fault current spinning motors add in the first cycle.
VFD Reflected-Wave Cable Length Limit - The reflected-wave overvoltage on a long VFD-to-motor cable.
Rotary Phase Converter Idler Sizing - The minimum rotary-phase-converter idler to make three-phase from single-phase.
Motor Across-the-Line Acceleration Time - How long a motor takes to bring its load up to speed started direct across the line.
Motor RMS Horsepower for a Duty-Cycle Load - The smallest continuous-rated motor that will not overheat on a repeating on/off (duty-cycle) load.
Reduced-Voltage Starter Current and Torque - Why an autotransformer's line current is the tap squared.
Insulation Resistance PI / DAR (Megger Test) - The polarization index (PI) and dielectric absorption ratio (DAR) from a timed insulation-resistance (megger) test.
Dwelling Service/Feeder Conductor at 83% (NEC 310.12) - Why a 200 A house runs on 2/0 copper instead of the 3/0 a straight table lookup demands.
Continuous-Load OCPD and Conductor at 125% (NEC 210.20 / 215.3) - The single most reused NEC sizing step, standalone.
Generator Output Conductor at 115% (NEC 445.13) - The conductor rule from a generator to its first overcurrent device, which estimators routinely get wrong.
Existing-Facility Load by Peak Demand (NEC 220.87) - Adding load without a service upgrade, on the metered peak.
EV Load-Management (EVEMS) Diversified Load (NEC 625.42) - The diversified service load of a bank of EV chargers under a NEC 625.42(A) energy management system.
EV Charger Throttled-Current Schedule (NEC 625.42) - What each car actually gets when an EV energy management system throttles.
NEC Pull and Junction Box Sizing - The minimum pull or junction box dimension for large raceways under NEC 314.28.
Lumen-Method Luminaire Count - How many fixtures to hit a target maintained footcandle level in a room, by the IES lumen method.
Room Cavity Ratio (RCR) for CU Lookup - The room cavity ratio needed to read a luminaire's coefficient of utilization.
Luminaire Spacing-to-Mounting-Height Ratio - The maximum center-to-center spacing between luminaires for reasonably uniform light.
Grounding Electrode Conductor Sizing - The grounding electrode conductor (GEC) from the largest ungrounded service conductor per NEC Table 250.66.
Bonding Jumper Sizing (Supply-Side and Equipment) - Supply-side and equipment bonding jumper sizing from the NEC tables.
Minimum Conductor Size for a Voltage-Drop Target - The smallest copper or aluminum conductor that holds voltage drop under a target percent.
Maximum Circuit Length for a Voltage-Drop Target - The longest one-way run that still meets a voltage-drop target.
Conduit Nipple 60% Fill (NEC Ch. 9 Note 4) - The conductor fill allowed in a NIPPLE -- a raceway no longer than 24 in between boxes, cabinets, or wireways.
Open-Delta (V-V) Transformer Bank Capacity - The balanced three-phase capacity of an open-delta (V-V) bank.
Motor Synchronous Speed, Slip, and Rotor Frequency - The synchronous speed Ns = 120 x frequency / poles, the slip relative to the nameplate full-load speed.
Motor Pole Count from Nameplate RPM - For a tech who only reads a speed off the plate.
Motor Shaft Torque, Horsepower, and Speed - The horsepower-speed-torque triangle T = 5252 x HP / RPM, solving either way.
Motor Input Power, Annual Energy, and Cost - The input kilowatts a motor draws at its efficiency (HP x 0.746 x load / efficiency).
Motor Run Hours for an Energy Budget - The run hours an annual energy budget buys.
Feeder for a Group of Motors (NEC 430.24 / 430.62) - Feeder conductor and overcurrent device for several motors on one feeder.
Conductor Short-Circuit Thermal Withstand (Onderdonk / ICEA) - Whether a conductor survives the fault current for the device's clearing time.
PVC Conduit Thermal Expansion (NEC 352.44) - Length change of a PVC raceway over its temperature swing, against the NEC trigger.
PVC Conduit Max Run Before an Expansion Fitting - The longest straight PVC run between anchors before an expansion fitting is required.
EGC Proportional Upsize for Increased Conductors (NEC 250.122(B)) - When ungrounded conductors are increased in size for voltage drop or future capacity.
Wye / Delta Line-to-Phase Voltage and Current - The mapping between line and phase (winding) quantities for both three-phase connections.
Feeder Tap Conductor 10-ft / 25-ft Rule (NEC 240.21(B)) - Minimum ampacity for an unprotected feeder tap under the 10-ft and 25-ft rules.
Buck-Boost Transformer Sizing (Single-Phase) - The autotransformer (buck-boost) kVA to correct a line voltage up or down for a load.
Wireway / Auxiliary Gutter 20% Fill (NEC 376.22) - Sizes a metal wireway (and, by 366.22, an auxiliary gutter) against the NEC 376.22 limits.
Rooftop Conduit Sunlight Ambient Adder (NEC 310.15(B)(2)) - Applies the NEC 310.15(B)(2) rooftop sunlight adder, 33 C (60 F) where a raceway is less than 7/8 in above the roof.
Working-Space Clearance Lookup (NEC 110.26) - Returns the NEC 110.26(A) working space in front of electrical equipment.
Household Range Demand Load (NEC Table 220.55 Col. C) - The demand load for household electric ranges by NEC Table 220.55 Column C, with the Note 1 over-12 kW increase.
Household Clothes Dryer Demand Load (NEC 220.54) - The clothes-dryer feeder/service demand under NEC 220.54.
Feeder/Service Neutral Demand Load (NEC 220.61) - Sizes the feeder/service neutral under NEC 220.61.
Motor Derating for Voltage Unbalance (NEMA MG-1) - Turns a measured voltage unbalance into a NEMA derating factor and a do-not-operate flag.
Point-Method Illuminance (Inverse-Square + Cosine) - Horizontal illuminance at a point from a luminaire of known candlepower by the IES point method.
Luminaire Mounting Height for a Target Illuminance - The mounting height that lands a target horizontal illuminance at a point.
Point-Method Required Candela for a Target - The luminous intensity a fixture must aim toward a point to hit a target illuminance.
Lighting Light-Loss Factor (Maintained/Initial) - Light-loss factor from the IES recovery factors, and the maintained lumens it yields.
Lighting Illuminance Uniformity Ratio - Avg/min, max/min, and U0 = min/avg from a grid of illuminance readings, against a target ratio.
Egress Lighting Illuminance Compliance Check (NFPA 101 / IBC) - Egress illuminance against NFPA 101 / IBC.
Industrial Control Panel SCCR (UL 508A) - The short-circuit current rating of an industrial control panel by the UL 508A weakest-link method.
Tolerable Step and Touch Voltage (IEEE 80) - The IEEE Std 80 tolerable step and touch voltages a grounding grid is checked against.
Ground Potential Rise Screen (IEEE 80) - Ground potential rise in a substation yard.
Lightning Rolling-Sphere Zone of Protection - The ground area a lightning mast or air terminal shields, by the NFPA 780 rolling-sphere method.
Max Grounding-Grid Resistance for the GPR Screen (IEEE 80) - The grid resistance that keeps ground potential rise within the tolerable touch voltage.
Neutral Grounding Resistor Sizing (IEEE 142) - Sizing the NGR off line-to-neutral, not line-to-line.
Ground Grid Conductor Sizing for Fault Current - The smallest grounding-grid conductor that survives a fault long enough for protection to clear it.
Overcurrent Selective Coordination Screen - Whether two overcurrent devices in series will let the downstream one clear a fault alone.
Current-Limiting Let-Through and Downstream Withstand - Whether a current-limiting device's let-through protects the conductor and equipment behind it.
Underground Burial Cover-Depth Lookup (NEC Table 300.5) - Returns the minimum cover for underground wiring by method and location from NEC Table 300.5 (<= 1000 V).
Raceway / Cable Support-Spacing Lookup (NEC Chapter 3) - The securing and support intervals for the common wiring methods from their NEC Chapter 3 .30 sections.
Motor Branch-Circuit Protection and Disconnect (NEC 430.52 / 430.110) - Maximum motor branch-circuit protective device and its disconnect.
Commercial General-Lighting and Receptacle Load (NEC 220.12 / 220.44) - Commercial general-lighting and receptacle load, with the NEC demand factors.
Noncoincident Loads: Larger of Heating vs A/C (NEC 220.60) - Applies NEC 220.60: where two loads (electric heat vs air-conditioning) are unlikely to run at the same time.
VFD Retrofit Energy and Cost Savings (Affinity Cube Law) - The number that sells a variable-frequency drive: the annual kWh and dollars it saves on a centrifugal pump or fan.
LED Lighting Retrofit Savings and Payback - The four numbers on every lighting proposal.
Power-Factor Correction Demand-Billing Savings - The dollars a power-factor capacitor returns.
PV Circuit Maximum Current and Ampacity (NEC 690.8, the 156% Rule) - PV circuit maximum current and the minimum conductor ampacity it requires.
PV Annual Energy, Specific Yield, and Capacity Factor - The first question a solar customer asks, answered with the NREL PVWatts energy model.
PV Array Size from a Target Annual Energy - The DC array size needed to offset a target annual production.
PV Inter-Row Spacing and Ground-Coverage Ratio - The row layout for a ground mount, carport, or ballasted flat roof.
PV Shade-Free Sun Angle from Row Pitch - With the row pitch fixed by the roof or lot, the lowest solar profile (elevation) angle the layout stays shade-free to.
Sun Shadow Length - The ground shadow a vertical object casts on level ground.
Solar Azimuth (Sun Compass Bearing) - The sun's compass bearing (clockwise from true north: 90 = east, 180 = south, 270 = west).
Solar Altitude / Winter-Design Sun Elevation - The sun's elevation angle above the horizon.
PV Inverter Loading Ratio (DC:AC) and Clipping Onset - The array-to-inverter power match: the inverter loading ratio (DC nameplate over AC rating, the DC:AC or ILR).
PV Cell Temperature and Temperature-Derated Power - Cell temperature by the NOCT model, and the temperature-derated power it produces.
PV Max Ambient Temperature for a Target Power - The highest ambient temperature a module still makes a target power.
PV Performance Ratio from Stacked Losses - Performance ratio as the product of the PVWatts-style derate stack.
PV Source-Circuit Fuse Sizing (NEC 690.9) - PV source-circuit overcurrent per NEC 690.9.
Battery Time-of-Use Arbitrage Value - What a time-of-use spread actually pays a grid-tied battery.
Battery Peak-Shaving Demand-Charge Savings - Sizes a battery to shave a commercial demand peak and prices it.
Battery C-Rate: Deliverable Power and Discharge Duration - How fast a battery can discharge (C-rate), and how much of that reaches the panel.
Transformer K-Factor From the Harmonic Spectrum (UL 1561) - Computes the transformer K-factor from a measured harmonic current spectrum.
Max Capacitor kVAR at Motor Terminals (Self-Excitation Limit) - Returns the largest power-factor capacitor that can be switched with a motor before self-excitation overvoltage.
Series R-L-C Reactance, Impedance, and Resonant Frequency - The base AC-circuit relations behind filter, coil, and cable-reactance work.
Harmonic Parallel-Resonance Order - Why a bigger PF cap bank can land on the 5th harmonic, the check pf-correction never makes.
Max PF Capacitor Bank to Keep Resonance Off a Harmonic - The largest PF capacitor bank that keeps the parallel-resonance order at or above a target.
Total Demand Distortion Limit Check (IEEE 519-2022) - The distortion limit that loosens as the supply gets stiffer, the number a utility actually holds you to at the PCC.
Conduit Bends Between Pull Points (360-Degree Rule) - Sums conduit bend angles against the 360-degree limit between pull points.
Shock Approach Boundaries (NFPA 70E Table 130.4) - Looks up the NFPA 70E Table 130.4 AC shock approach boundaries by nominal voltage.
Conduit Jam Ratio for Three Same-Size Conductors (NEC Ch. 9) - Three same-size conductors can wedge in a bend when the conduit ID / conductor OD ratio lands in the ~2.8-3.2 band.
Premium Motor Upgrade Energy Savings - The annual energy and dollars a premium-efficiency motor saves over the one it replaces.
Transformer Loading Efficiency and Losses - The efficiency and losses of a transformer at a given load.
Economic Conductor Sizing (I2R Payback) - Whether upsizing a conductor pays for itself in reduced I^2R heat loss.
Generator Fuel Runtime and Backup Duration - How long a standby generator runs on its fuel, the fuel-supply companion to generator-sizing and battery-runtime.
Transformer Turns / Voltage / Current / Impedance Ratio - The transformer turns ratio a = Np/Ns, which equals the voltage ratio Vp/Vs, the inverse current ratio Is/Ip.
Transformer Voltage Regulation from %R and %X - What the secondary voltage actually does under load.
Capacitor Discharge Time and Bleed Resistor (NEC 460.6) - Sizes the bleed resistor that keeps a switched-off power-factor or DC-bus capacitor from staying lethal.
Asymmetrical and Peak Fault Current from X/R - The first-cycle fault current the symmetrical value hides.
Battery Room Hydrogen Ventilation (IEEE 1635) - The cells-not-jars exhaust rate that keeps a battery room under the LEL.
Battery Room Max Charge Current from Available Airflow - The highest maximum charge current a room's exhaust can safely support.
Transformer Inrush Coordination Point - Why a code-legal primary device still trips on energization.
Termination Temperature Ampacity Limit (NEC 110.14(C)) - Usable ampacity is the lesser of the termination column and the derated 90 C value.
Swimming-Pool Equipotential Bonding Checklist (NEC 680.26) - The NEC 680.26 equipotential bonding checklist, by pool type.
Electric Strike and Maglock Power, Inrush, and Standby Budget - Access control power supplies get sized on the doors and then fail on the battery.
Maglock Effective Holding Force at the Door Handle - A 1,200 lb maglock does not resist 1,200 lb at the handle, and where it is mounted decides how much it does.
Wind Turbine Tip-Speed Ratio and Rotor Speed - Tip speed ratio is the number that says whether a rotor is running where it makes power.
Wind Power Density, the Betz Limit, and Rotor Output - Wind power goes as the CUBE of speed, which is why siting beats equipment.
Wind Shear Power-Law Speed at Hub Height - Wind measured at a met tower is not the wind at the hub.
Wind Weibull Distribution, Annual Energy, and Capacity Factor - Annual energy does not come from average wind speed, it comes from the DISTRIBUTION.
Wind Turbine Output Air-Density Correction - A power curve is warranted at sea level and 59 degF.
Wind Turbine Yaw Misalignment Power Loss - A turbine pointing twelve degrees off the wind loses 6.41% of its output.
Gin-Pole and Uptower Component Lift Load - The head of a gin pole carries roughly TWICE the weight of the part being lifted.
Ruling (Equivalent) Span for a Line Section - The ruling span is not the average span and it is not the longest span.
Conductor Sag Change With Temperature - Two things fight each other when a conductor heats up.
Conductor Blowout and Horizontal Clearance - Ground clearance is checked straight down and nothing checks sideways.
Suspension Insulator Uplift Check at a Low Point - In hilly country a suspension structure sitting in a sag between two higher structures can be lifted rather than loaded.
Overhead Line Ground Clearance - Clearance is the reason sag matters, and the arithmetic connecting them is a subtraction nobody writes down.
Wood Pole Class and Groundline Moment - A wood pole is rated by class, and the class is a statement about ONE number.
Guy Anchor Holding Capacity in Soil - The guy-tension calculator gives the pull in the guy.
Transverse Wind Load on Conductor and Pole - The load that governs a distribution structure on a windy day is not the conductor tension.
NESC Ice-and-Wind District Loading on a Conductor - Everything downstream of a conductor -- sag, tension, pole moment, guy pull.
Conductor Long-Term Creep and Sag Increase - A conductor sags more in year ten than in year one, at the same temperature and the same load, because aluminium creeps.
Sagging by Stopwatch (Return-Wave Method) - Sagging by eye against a target works when a crew can see both structures, and often they cannot.
Distribution Transformer Diversified Loading - A 25 kVA pot serving eight houses is not serving eight times one house's peak, because the peaks do not coincide.
Line Capacitor Bank Voltage Rise - Switching a capacitor bank onto a feeder raises the voltage.
Line Voltage Regulator Tap and Bandwidth - A step voltage regulator has three settings that interact -- set voltage, bandwidth, and time delay.
Recloser-to-Fuse Coordination Screen - A recloser's fast curve is supposed to clear a temporary fault before the branch fuse melts.
Distribution Feeder I2R Loss and Loss Factor - Feeder losses are not average current squared times resistance, and the gap is wide enough to change a decision.
Watt-Hour Meter CT / PT Multiplier - A transformer-rated meter does not read energy, it reads a scaled fraction of it.
Counterpoise and Radial Ground Array Resistance - A driven rod is the standard electrode and in rock it is not an option.

Electrical

Tools in this group

Other trades