⚡ SparkRef

Wire Ampacity Calculator
Allowable ampacities — copper & aluminum, 60/75/90°C insulation
60°C = 140°F · 75°C = 167°F · 90°C = 194°F
Conduit Fill Calculator
Conduit fill percentages & conductor/conduit dimensions
Fill Rules — Max Fill by Conductor Count
# ConductorsMax Fill %
1 Conductor53%
2 Conductors31%
3+ Conductors40%
Conduit Jam Ratio Calculator
ICEA/NEMA cable-pulling guideline — 3-conductor jam-risk analyzer
About Jam Ratio
Jam zone · JR ≈ 3.0 cables wedge Safe · JR > 3.2 cables shuffle past

When pulling exactly three equally-sized conductors through a conduit with two or more 90° bends, the ratio of conduit inside diameter (ID) to conductor outside diameter (OD) can land in a narrow danger zone where the three conductors align into a rigid triangular wedge and physically lock inside the conduit. This can happen even when fill percentage passes.

Jam RatioVerdict
JR < 2.8Safe — conductors too large to wedge
2.8 ≤ JR ≤ 3.2Jam risk — can lock in bends
JR > 3.2Safe — conductors have room to reposition

Applies only to 3-conductor pulls with 2+ 90° bends. For 2 or 4+ conductors, or straight pulls, jam ratio is not a concern.

Box Fill Calculator
Outlet & junction box fill volume calculator
Preset:
Every allowance (grounds, clamps, devices, supports) is counted at this size even if smaller conductors are also in the box — that's the NEC rule.
Conductor Count
Volume Allowances by Wire Size
AWGVolume per Conductor
142.00 in³
122.25 in³
102.50 in³
83.00 in³
65.00 in³
Rules: Grounds = 1× largest conductor. Clamps = 1× largest. Each device/yoke = 2× largest. Support fittings = 1× largest.
Cable Lube Estimator
Planning volume for a conduit pull — start-of-job estimate
Field Guidance

Why lube matters: drops conductor friction 50–80%, protects insulation from chafing through bends, saves your back on long pulls. A dry pull through multiple 90°s can physically damage the jacket — and the cost of a reel of cable dwarfs the cost of a quart of lube.

Rule of thumb: ~1 quart per 100 ft at 40% fill in a 2" conduit. Scales up with conduit size and fill %, and with length.

How to apply: coat the cable heavily at the mouth of the conduit as it feeds in — don't pre-pour into the pipe. On long pulls re-lube the feed every ~50 ft so the cable keeps carrying a fresh coat. On tough pulls do a "basket pass" first — pull a lube-soaked rag or lube-impregnated roping ahead of the cable to pre-coat the interior.

Buy more than you need: running out mid-pull is worse than paying for an extra quart. Leftover keeps for the next job.

Tough pull factors: long runs (>300 ft), 2+ 90° bends, high fill (>40%), stiff or XLPE-jacketed cable, cold weather, dry lube from prior coat — bump 1.5× to 2×.

Estimate based on general cable-pulling-lube guidelines. Always check the lubricant manufacturer's coverage spec for the specific product you're using.

Voltage Drop Calculator
Branch circuit & feeder voltage drop — single & three phase
PF 1.0 for resistive loads (heaters, incandescent) · ~0.85 for motor loads.
Voltage Drop Guidelines
Branch Circuit
Max 3% voltage drop recommended on branch circuits
Feeder
Max 3% voltage drop recommended on feeders (5% total branch + feeder)
Total (Feeder + Branch)
Max 5% total voltage drop recommended for efficiency
The Four Quantities — V · I · R · P
V Voltage (volts)
Electrical pressure. How hard the electrons are being pushed through the wire. Higher voltage = stronger push.
I Current (amps)
Flow rate. How many electrons move past a point per second. Current is what actually does the work — and what sizes the wire.
R Resistance (ohms · Ω)
Opposition to flow. Higher R = less current for the same voltage. Every conductor, connection, and load has some resistance; that's where voltage drop comes from.
P Power (watts)
Work per second. Volts × Amps = watts of real work being done — heat, light, motion. All load ratings (HP, kW, BTU) come back to this.
Electrical Laws Calculator
Tip: values accept k / M / m prefixes — type 5k for 5000 Ω, 2.2M for 2.2 MΩ, 50m for 0.050 A.
Ohm's Law Formulas
Voltage
V = I × R
Voltage (V) = Current (A) × Resistance (Ω)
Current
I = V / R
Current (A) = Voltage (V) ÷ Resistance (Ω)
Resistance
R = V / I
Resistance (Ω) = Voltage (V) ÷ Current (A)
Power Formulas
Power (basic)
P = V × I
Watts = Volts × Amps
Power (from resistance)
P = I² × R  |  P = V² / R
Used when voltage or current is unknown
Ohm's Law / Power Wheel — All 12 Formulas
Voltage · V
V = I × R
V = P ÷ I
V = √(P × R)
Current · I
I = V ÷ R
I = P ÷ V
I = √(P ÷ R)
Resistance · R
R = V ÷ I
R = V² ÷ P
R = P ÷ I²
Power · P
P = V × I
P = I² × R
P = V² ÷ R
Each row = one unknown solved from two knowns. DC only (for AC with power factor, see HP/Power).
HP / Power / Amps Converter
Cross-reference any power unit — get watts, amps, HP, kVA, BTU
Quick pick:
Calculator
Fractions · feet-inches · trig · PEMDAS
0
Benfield Presets tap to insert · edit the numbers
How to use the Calculator
Entering numbers
  • 14 — whole inches
  • 14.375 — decimal inches
  • 5/8 — a pure fraction (inches)
  • 2 space 3/8 — a mixed number (tap space between the whole and fraction)
  • 1' 2 3/8 — full feet-inches (feet button auto-inserts the space after ')
  • -5 or tap ± to flip the sign of the current value
Math & order of operations
  • Standard PEMDAS: 2 + 3 × 4 = 14, use parens to override
  • All four operators: + − × ÷
  • Trig in DEGREES: sin, cos, tan, csc (cosec), cot
  • Square root: √ button inserts sqrt(
Precision toggle (1/8″ ↔ 1/16″)

Changes how the result is rounded for display. 1/8″ matches most tape measures and is the field default. Switch to 1/16″ for finer work (cabinetry, panel layout). Your input is never rounded — only the displayed result.

Tape

Tap Tape to show your last 20 calculations. Tap any entry to pull its result back into the expression for re-use.

Memory slots (M1–M5)

Five memory slots live at the top of the keypad for values you want to reuse. Each slot shows its stored value once filled.

  • Tap a slot → recalls the stored value into your expression (appends it)
  • Long-press a slot (hold ½ second) → stores the current result; overwrites if already filled
  • Tap the × badge on a filled slot → clears just that slot
  • Toasts confirm every action (M1 ← 1' 4″, M1 cleared, etc.)

Field example: Running a series of 8″ offsets at 30° across a multi-pipe rack. Store the mark spacing (8 × csc(30) = 1′ 4″) in M1. On each pipe, mark the first bend, recall M1, tap +, enter the first mark, hit = — the second mark pops out. M1 stays ready for every pipe in the rack.

Heads up: Tape and Memory both reset when you reload the app. Persistent tape + labeled memory slots are a planned update.

Benfield preset chips

Below the keypad you'll find 4 tappable preset pictograms: an offset zigzag, an offset shrink (zigzag with a small bracket on top), a 3-Pt saddle hump (with a dot showing the obstacle), and a saddle shrink (hump with a bracket on top). These are the formulas from Jack Benfield's manual, pre-filled with placeholder numbers you can change in place. The two Offset pictograms pair together (distance + shrink at any angle); the two Saddle pictograms pair together (distance + shrink at the locked 45°/22.5° field standard).

Workflow:

  1. Tap a preset → the formula loads in the display and the preset parameter bar appears. The first placeholder (e.g. the offset depth) is already highlighted amber — ready for your value.
  2. Tap any number in the display to edit it. Every number is tappable (dashed underline). Tap → it highlights amber → your next digit replaces it. Keep typing to extend (e.g. 5 then 0 gives you 50). A blinking caret shows exactly where your next digit will land.
  3. For angles on the two Offset presets, use the one-tap chips in the bar (10° · 22.5° · 30° · 45° · 60°). Tapping an angle chip rewrites the angle inside the active preset's trig call (csc, cot, etc.) so you can flip angles without retyping. The two Saddle presets lock the angle at 22.5°/45° (the field-standard 3-point saddle) — only the rise is editable.
  4. Tap an operator or function → selection/caret clears and further input appends at the end. Tap an empty part of the expression to deselect manually.
  5. Tap = to lock it in; the tape records it, the result glow brightens to show it's committed, and long-pressing a memory slot saves it.
  6. Made a mistake? Tap Undo (bottom-right of the keypad, same row as space) to reverse the last destructive action — preset load, angle swap, clear, or equals.
  7. Dismiss the preset bar with its × when you're done; it does NOT dismiss on its own so the swap chips stay available while you iterate.

Example: 5″ offset at 22½° bend → tap Offset → the 8 is already selected, type 5 → tap 22.5° in the bar → tap =. Expression becomes 5 × csc(22.5) = 1' 1 1/16″. No backspacing, no re-typing the whole formula.

3-point saddle example: 3″ rise over a 2″ pipe → tap 3-Pt Saddle → the 2 is already selected, type 3 → =. Expression becomes 3 × csc(22.5) ≈ 7 13/16″ (distance from center mark to each side mark). Then tap Saddle Shrink → type 3 → = to get the shrink correction.

For the full math behind each preset (when to use which), expand the Conduit bending math (Benfield) section below.

Chaining calculations

Press = and the result replaces your expression so you can keep going. Example: compute 8 × csc(30) = 1' 4″, press =, then − 2 = to subtract 2″.

Live preview vs. equals

As you type, the amber result updates live — useful for checking your expression before committing. = locks it in and writes to the Tape.

Conduit bending math (Benfield)

Sections below match the preset chip order under the keypad. Each preset loads the corresponding formula with editable parameters.

Offset — 2-bend cosecant method
distance between bends = offset × csc(θ)

Classic Benfield offset. Offset is how far you need to jog the raceway sideways. θ is the bend angle — same on both pulls. Pull the first bend, flip the pipe flat, measure to the second mark, pull the second bend at the same angle.

Example: 8″ offset at 30° → 8 × csc(30) = 1' 4″. Mark the first bend, measure 16″ down the pipe, mark the second bend, pull both at 30°.

How to use this preset: Tap Offset. The 8 is pre-selected — type your offset depth. Then tap an angle chip (10° / 22.5° / 30° / 45° / 60°) in the bar above the keypad to change the bend angle. Hit = when done.

Offset Shrink — what the offset "eats"
shrink = offset × ( csc(θ) − cot(θ) )

Shrink is the pipe length lost to the bend itself — the finished run covers less distance end-to-end than the stick you started with. Pipe comes in 10' lengths, so the practical question isn't "what do I cut?" — it's "how far will my stick actually reach after I put this offset in it?"

Example: 8″ offset at 30° → 8 × (csc(30) - cot(30)) ≈ 2 1/8″ of shrink. A 10' stick bent with that offset covers 9' 9 7/8″ end-to-end (10' minus 2 1/8″). Need the run to reach a full 10'? Put a coupling past the offset, or land the offset where the 9' 9 7/8″ coverage is enough — don't plan on ordering a non-standard pipe length.

How to use this preset: Tap Offset Shrink. The 8 is pre-selected — type your offset depth. Tap an angle chip to match the bend angle you're pulling. Same angle chips as the Offset preset, so the pair works as a quick "distance-then-shrink" check.

3-Point Saddle — over a round obstruction
distance from center mark to each side mark = rise × csc(22.5°) ≈ rise × 2.6

A 3-point saddle clears a round obstacle (a pipe, a beam, a conduit crossing your run) with three bends: a center bend at 45° that goes up and over, and two side bends at 22.5° each that bring the pipe back flat. The center bend is always twice the side angle. The 45°/22.5° combination is the field standard — multipliers and shrink work out clean, and it clears most real-world obstructions (1″–3″ pipes) without a ridiculous rise.

Rise = obstruction diameter + any clearance you want. For a 1″ pipe with 1″ of clearance, use 2″ rise.

Example: 2″ rise over a 1″ pipe → 2 × csc(22.5) ≈ 5 1/4″. Mark the center of your saddle on the obstacle, measure 5 1/4″ outward in each direction for the side marks. Pull the center bend first (45°), then the two side bends (22.5° each) in the opposite direction, keeping the pipe flat between pulls.

How to use this preset: Tap 3-Pt Saddle. The 2 is pre-selected — type your rise. Hit =. The angle is locked at 22.5° (side) / 45° (center) — the standard that matches the 3/16″ shrink rule. For non-standard saddle angles, type the expression manually: rise × csc(your-side-angle).

Saddle Shrink — what the 3-point saddle "eats"
shrink = rise × ( csc(22.5°) − cot(22.5°) ) ≈ rise × 3/16″

The 3-point saddle behaves like a single 22.5° offset for shrink purposes — the center bend pushes the pipe up, the two side bends bring it back, and the net loss of end-to-end coverage equals one 22.5° offset's shrink. Field rule of thumb: about 3/16″ of shrink per inch of rise.

Example: 2″ rise → 2 × (csc(22.5) - cot(22.5)) ≈ 3/8″ of shrink. Shift your center mark 3/8″ toward your reference end so the finished saddle lands dead-center on the obstacle instead of past it.

How to use this preset: Tap Saddle Shrink. The 2 is pre-selected — type your rise (same value you used for the 3-Pt Saddle preset). Hit =. Angle is locked at the 22.5° field standard to match the 3-Pt Saddle preset.

Math source: Jack Benfield's Benfield Conduit Bending Manual. Always verify takeoff and deduct values against your specific bender and conduit type. The app is a reference — your eyes and the pipe are the final authority.

Wire Size Explorer tap any wire — drawn to actual scale
Scroll → Smallest (16 AWG) on the left grows to 2000 kcmil on the right.
Ampacity Chart
how amperage scales across the whole wire-size range
60°C = 140°F (TW, rare) · 75°C = 167°F (THW/THWN) · 90°C = 194°F (THHN/XHHW, most common)
Tap any point on a curve for the exact value.
Apprentice read: see how the curves flatten at bigger sizes? Doubling the wire doesn't double the ampacity once you're past 4/0 — you run into heat-dissipation limits. That's why long/high-current feeders often run in parallel instead of one giant conductor.
Compare Conductors tap up to 4 sizes

Pick up to 4 conductor sizes to see their properties side-by-side. Toggle between copper and aluminum to see how material shifts ampacity and resistance for the same physical size.

Pick up to 4 to compare
Quick pairs:
Apprentice tip: notice how doubling the cross-section roughly halves the resistance but only bumps ampacity by 30–40%. That's why long feeder runs upsize for voltage drop before ampacity — voltage drop is the harsher limit on long pulls.
Motor Full-Load Amps pick HP + voltage/phase

Info

Field Reference & About
First time here? Quick start

Five paths through the app, depending on what you're doing on the job right now:

  • Working on a feeder pull? Calculations → Ampacity sizes the wire. Jump from there to V-Drop to confirm the run length won't eat too much voltage.
  • Bending conduit? Calculations → Calculator. Tap the Offset preset (or Offset Shrink / 3-Pt Saddle / Saddle Shrink), tap the highlighted number to type your value, tap an angle chip. Feet-and-inches math with fractions, no classroom.
  • Sizing a box? Calculations → Box Fill. Tap a preset scenario (single switch, duplex recep, 3-way, etc.) to prefill the counts. Result shows every standard metal box that has room for your fill.
  • Learning the trade? Visuals tab is the teaching star. The Ampacity Chart shows how amps scale across every wire size and temp rating; the Wire Explorer draws each conductor at true relative scale.
  • Every calc gives a number — always cross-check. SparkRef is a field calculator, not a code substitute. Read the Disclaimer card and keep your codebook (or Ugly's) on the truck for the official word.

Tap the summary above to collapse this once you've got your bearings.

Electrical Symbols (ANSI/IEEE)
Duplex Outlet
GFCI
GFCI Outlet
WP
Weatherproof
Quad Outlet
240V
240V Outlet
S
Switch (SP)
S3
3-Way Switch
S4
4-Way Switch
SD
Dimmer
Ceiling Light
Wall Light
Recessed Can
Fluorescent
EXIT
Exit Sign
SD
Smoke Detector
T
Thermostat
Panel
Junction Box
M
Motor
Ground
Standard ANSI/IEEE architectural electrical symbols. Symbols may vary by specification and region.
NEMA Receptacle Configurations
2-Pole, 2-Wire — Ungrounded (Legacy)
1-15R
125V 15A
Legacy 2-prong
2-20R
250V 20A
Legacy ungrounded
2-30R
250V 30A
Legacy ungrounded
Ungrounded outlets are no longer code-compliant for new installations in most jurisdictions. Existing installations may remain, but replacements should be a 5-15R (grounded) or a GFCI device with proper "No Equipment Ground" labeling.
Straight-Blade (Non-Locking)
5-15R
125V 15A
Standard outlet
5-20R
125V 20A
T-slot (20A only)
5-30R
125V 30A
RV, commercial
5-50R
125V 50A
High-amp 120V
6-15R
250V 15A
240V appliance
6-20R
250V 20A
A/C, compressors
6-30R
250V 30A
A/C, large loads
6-50R
250V 50A
Welder, shop
7-15R
277V 15A
Commercial lighting
7-20R
277V 20A
Commercial HID
7-30R
277V 30A
Commercial HVAC
TT-30R
125V 30A
RV shore power
Twist-Lock (NEMA L-Series)
L5-15R
125V 15A Locking
Light commercial
L5-20R
125V 20A Locking
Twist-lock
L5-30R
125V 30A Locking
Stage, data center
L6-15R
250V 15A Locking
240V twist-lock
L6-20R
250V 20A Locking
Industrial 240V
L6-30R
250V 30A Locking
Industrial 240V
L5-50R
125V 50A Locking
Industrial / stage
L6-50R
250V 50A Locking
Heavy 240V industrial
L7-15R
277V 15A Locking
Commercial lighting
L7-20R
277V 20A Locking
Commercial lighting
L7-30R
277V 30A Locking
Commercial HVAC
L8-20R
480V 20A Locking
Heavy industrial
L9-20R
600V 20A Locking
High-voltage industrial
Straight-Blade Split-Phase (Legacy 125/250V)
10-30R
125/250V 30A
Legacy dryer
10-50R
125/250V 50A
Legacy range
Straight-Blade 3-Phase (250V, no ground, no neutral)
11-15R
250V 3ø 15A
3 hots, no ground
11-20R
250V 3ø 20A
3 hots, no ground
11-30R
250V 3ø 30A
3 hots, no ground
Twist-Lock
L10-30R
125/250V 30A Locking
Legacy split-phase
L11-20R
250V 3ø 20A Locking
3 hots, no ground
L11-30R
250V 3ø 30A Locking
3 hots, no ground
L12-20R
480V 3ø 20A Locking
Heavy industrial
L12-30R
480V 3ø 30A Locking
Heavy industrial
L13-30R
600V 3ø 30A Locking
High-voltage industrial
3P 3W includes both legacy split-phase (10-series, 125/250V, no ground) and 3-phase without neutral (11, L11-L13). All lack a separate equipment ground — replaced by 3P 4W (14/15-series + L14-L17) in modern installations.
Straight-Blade Split-Phase (125/250V)
14-20R
125/250V 20A
Shop / commercial
14-30R
125/250V 30A
Modern dryer
14-50R
125/250V 50A
Range / EV charger
14-60R
125/250V 60A
Large range
Straight-Blade 3-Phase (250V, 3 hots + ground)
15-20R
250V 3ø 20A
3 hots + ground
15-30R
250V 3ø 30A
3 hots + ground
15-50R
250V 3ø 50A
3 hots + ground
15-60R
250V 3ø 60A
3 hots + ground
Twist-Lock
L14-20R
125/250V 20A Locking
Portable equipment
L14-30R
125/250V 30A Locking
Generators, RVs
L14-60R
125/250V 60A Locking
Large generator
L15-20R
250V 3ø 20A Locking
3 hots + ground
L15-30R
250V 3ø 30A Locking
3 hots + ground
L15-60R
250V 3ø 60A Locking
Large 3-phase
L16-20R
480V 3ø 20A Locking
Industrial
L16-30R
480V 3ø 30A Locking
Industrial
L17-30R
600V 3ø 30A Locking
High-voltage industrial
Straight-Blade (Legacy, 3 hots + neutral, no ground)
18-15R
120/208V 3ø 15A
Legacy industrial
18-20R
120/208V 3ø 20A
Legacy industrial
18-30R
120/208V 3ø 30A
Legacy industrial
18-50R
120/208V 3ø 50A
Legacy industrial
18-60R
120/208V 3ø 60A
Legacy industrial
Twist-Lock
L18-20R
120/208V 3ø 20A Locking
Legacy industrial
L18-30R
120/208V 3ø 30A Locking
Legacy industrial
L19-20R
277/480V 3ø 20A
Heavy industrial (no ground)
L20-20R
347/600V 3ø 20A
High-voltage (no ground)
Legacy 3-phase configurations with neutral but no separate equipment ground. Largely replaced by NEMA 21/22/23-series (4P 5W) for all modern installations. If encountered, plan for conversion on retrofit.
Straight-Blade 208Y/120V 3-Phase
21-20R
208Y/120V 3ø 20A
3 hots + N + ground
21-30R
208Y/120V 3ø 30A
Commercial 3-phase
21-50R
208Y/120V 3ø 50A
Heavy commercial
21-60R
208Y/120V 3ø 60A
Large 3-phase
Straight-Blade 480Y/277V & 600Y/347V
22-20R
480Y/277V 3ø 20A
Heavy industrial
22-30R
480Y/277V 3ø 30A
Industrial
23-30R
600Y/347V 3ø 30A
High-voltage industrial
Twist-Lock 208Y/120V
L21-20R
208Y/120V 20A 3-Phase
Data center, IT
L21-30R
208Y/120V 30A 3-Phase
Server racks, PDUs
Twist-Lock 480Y/277V & 600Y/347V
L22-20R
480Y/277V 3ø 20A
Heavy industrial
L22-30R
480Y/277V 3ø 30A
Heavy industrial
L23-20R
600Y/347V 3ø 20A
High-voltage
L23-30R
600Y/347V 3ø 30A
High-voltage
AC Charging Connectors (Level 1 / Level 2)
J1772
SAE J1772 (Type 1)
L1: 120V 12-16A
L2: 240V up to 80A
NACS
NACS / J3400
Tesla + Ford/GM/Rivian
AC + DC combined
Type 2
IEC 62196 (Mennekes)
European Type 2
AC up to 22kW
DC Fast Charging Connectors
CCS1
CCS Type 1
Combined AC+DC
DC: 50–360 kW
CCS2
CCS Type 2 (Combo 2)
European DC fast
DC: 50–350 kW
CHAdeMO
CHAdeMO
Nissan Leaf, Mitsubishi
DC: up to 100 kW
GB/T
GB/T 20234 (China)
DC: up to 250 kW
Rare in NA
Common EVSE-Side NEMA Receptacles
These are the wall receptacles electricians most often install for Level 2 EV charging. Tap to jump to the full NEMA spec.
14-50R
Level 2 most common
240V 50A → 40A charge
14-30R
Dryer outlet reuse
240V 30A → 24A charge
6-50R
Welder outlet reuse
240V 50A → 40A charge
TT-30R
RV park / camper
120V 30A → 24A L1
L14-30R
Portable EVSE locking
240V 30A → 24A charge
Install tip: EVSE circuits should be sized at 125% of continuous load per standard code requirements. A 48A EVSE needs a 60A circuit. Most residential Level 2 installations land on a 40A circuit (50A breaker) with a 14-50R, feeding a 32A EVSE. GFCI is required for all Level 1/2 EVSE branch circuits.
Classification by poles (current-carrying blades) and total wires (including ground). First number = NEMA voltage/phase code, second = amp rating. "L" prefix = locking (twist-lock). R = receptacle, P = plug.
Circuit # → Phase Color
Black
PHASE A
Standard US 3-phase panel. Odd circuits = left side, even = right. Phases rotate A/B/C every two circuits. Verify against your panel's legend label — some manufacturers differ.
Electrical Formulas
Ohm's Law
V = I × R
Volts = Amps × Ohms  ·  I = V/R  ·  R = V/I
Power (DC / Resistive)
P = V × I
Watts = Volts × Amps  ·  P = I²R = V²/R
Power (Single-Phase AC)
P = V × I × PF
PF = power factor (0–1). For resistive loads PF = 1.
Power (Three-Phase AC)
P = √3 × VL × I × PF
VL = line-to-line voltage. √3 ≈ 1.732.
Power Factor Relationship
kW = kVA × PF
PF = kW ÷ kVA — the ratio of real power (work) to apparent power (what the utility sees). Resistive loads: PF = 1, so kW = kVA. Motors and lighting ballasts drop PF below 1.
Voltage Drop (Single-Phase)
VD = 2 × K × I × L / CM
K = 12.9 (Cu) or 21.2 (Al) · L = one-way ft · CM = circular mils. Recommended: ≤3% branch, ≤5% total (branch + feeder).
Voltage Drop (Three-Phase)
VD = √3 × K × I × L / CM
Same constants as single-phase; √3 factor replaces the 2.
Motor Horsepower → Amps (estimate)
A ≈ (HP × 746) / (V × Eff × PF)
Approximate — check the motor nameplate or a motor-sizing reference for the published FLA. Eff and PF default to ~0.85 if unknown.
Amps → Horsepower (estimate)
HP ≈ (V × I × Eff × PF) / 746
Reverse of HP→Amps — useful for estimating motor size from running current. Cross-check with the nameplate HP when available.
kVA → Amps (Single-Phase)
I = (kVA × 1000) / V
Line current for a 1Ø load rated in kVA. Example: 10 kVA at 240 V = 41.7 A.
kVA → Amps (Three-Phase)
I = (kVA × 1000) / (V × √3)
Line current for a 3Ø load rated in kVA. Example: 75 kVA at 480 V = 90.2 A.
Transformer Full-Load Current (1Ø)
IFL = (kVA × 1000) / V
Same math as kVA→Amps, framed for transformer primary/secondary sizing. Use the rated voltage of the side you're sizing — primary and secondary currents are computed independently.
Transformer Full-Load Current (3Ø)
IFL = (kVA × 1000) / (V × √3)
3Ø transformer full-load current. Primary amps and secondary amps scale inversely with their respective voltages (higher V side carries less current).
Short-Circuit at Transformer Secondary (3Ø)
ISC = (kVA × 100,000) / (V × √3 × %Z)
Available fault current at the transformer's secondary terminals. %Z is the transformer's per-unit impedance (typically 2–6%, printed on the nameplate). Actual fault current downstream is lower due to wire resistance — useful for sizing breaker interrupt ratings (AIC).
Pythagorean / Rolling Offset
c = √(a² + b²)
Right-triangle hypotenuse. For a rolling (3D) offset: true offset = √(rise² + set²). Also the go-to formula for squaring layouts, diagonal measurements, and any right-angle geometry in the field.
Offset Bend Multipliers
Mark Distance = Offset × Multiplier
10°: 6  ·  22.5°: 2.6  ·  30°: 2  ·  45°: 1.4  ·  60°: 1.15
Shrink per inch of offset  ·  10°: 1/16"  ·  22.5°: 3/16"  ·  30°: 1/4"  ·  45°: 3/8"  ·  60°: 1/2"
Watts ↔ BTU/hr
BTU/hr = W × 3.413
Convert electrical power to heat output. 1 kW ≈ 3,413 BTU/hr. Useful for panel-heat load, resistive heaters, or sizing enclosure cooling.
Cooling Tons ↔ BTU/hr
1 ton = 12,000 BTU/hr
HVAC unit of cooling capacity — the energy needed to melt 1 ton of ice over 24 hours. A 5-ton AC removes 60,000 BTU/hr.
Wire Resistance Temperature Correction
Rhot ≈ Rcold × (1 + α × ΔT)
α = 0.00393/°C (0.00218/°F) for copper, 0.00403/°C (0.00224/°F) for aluminum. ΔT = temperature rise. Wire resistance rises with temperature — measurable on long feeders running at full load, especially in hot spaces. Common terminal ratings: 60°C (140°F), 75°C (167°F), 90°C (194°F).
Conduit Fill %
Fill % = (Σ Wire Area ÷ Conduit Area) × 100
Max fill: 1 conductor = 53%  ·  2 conductors = 31%  ·  3+ conductors = 40%. Use the wire's insulated cross-section area, not bare-conductor area.
Conversion Table
AWG ↔ mm²
14 AWG
→
2.08 mm²
12 AWG
→
3.31 mm²
10 AWG
→
5.26 mm²
8 AWG
→
8.37 mm²
6 AWG
→
13.3 mm²
4 AWG
→
21.2 mm²
2 AWG
→
33.6 mm²
1/0 AWG
→
53.5 mm²
4/0 AWG
→
107 mm²
Length
1 inch
→
25.4 mm
1 foot
→
0.3048 m
1 meter
→
3.281 ft
1 mile
→
5280 ft
Power
1 HP
→
746 W (0.746 kW)
1 kW
→
1.341 HP
1 kW
→
3412 BTU/hr
1 ton (HVAC)
→
12,000 BTU/hr
Temperature
°F → °C
=
(°F − 32) × 5/9
°C → °F
=
(°C × 9/5) + 32
32 °F
=
0 °C
75 °F
=
23.9 °C
194 °F
=
90 °C
Torque
1 ft-lb
→
12 in-lb
1 ft-lb
→
1.356 N·m
1 in-lb
→
0.113 N·m
Pressure / Area
1 PSI
→
6.895 kPa
1 sq ft
→
0.0929 m²
1 kcmil
→
0.5067 mm²
Resistance (Copper, 75°C)
14 AWG
→
3.14 Ω/1000ft
12 AWG
→
1.98 Ω/1000ft
10 AWG
→
1.24 Ω/1000ft
8 AWG
→
0.778 Ω/1000ft
6 AWG
→
0.491 Ω/1000ft
How to Bend Conduit
Key Terms
Deduction — the distance a bender "eats" at the bend. Subtract from your measured length before marking.
Take-up (Stub-up) — for a 90°, distance from end of conduit to the back of the bend. EMT rule of thumb: ½"→5", ¾"→6", 1"→8", 1¼"→11".
Gain — distance saved by the curve of a bend vs. two straight sections meeting at a square corner. Matters on back-to-backs.
Developed length — total length of conduit consumed by a bend, measured along the centerline arc.
Centerline radius (CLR) — radius measured to the centerline of the conduit, not the inside or outside.
Shrink — how much shorter the run becomes after the bend (especially offsets and saddles). Always measure after accounting for shrink.
Spring-back — conduit relaxes slightly after the pressure comes off; over-bend by 2°–5° on tight bends to compensate.
Arrow — the bender's primary bend-alignment mark. Your pencil mark goes here for most pulls (stub-ups, offsets, saddles).
Star — back-of-bend indicator on many benders; used on back-to-back 90°s so the back of the finished bend lands on your mark.
Back-to-back — two 90°s on the same stick where the backs of both bends face each other. Three shapes depending on how you orient the pipe between pulls: a U (both stubs pointing the same direction — the classic stub-up / run / stub-up), a Z/S in one plane (one stub up, one stub down, both in the same flat layout), or a perpendicular Z/S (stubs in different planes — pipe rotated 90° between the pulls so the second stub comes out sideways relative to the first). Either way, the second mark goes on the star (back-of-bend) so the inside-to-inside dimension between the two bends equals what you measured. Miss this and the pipe lands one deduction long.
Dog leg — when the two bends of an offset aren't in the same plane. The pipe twists out of square between pulls, so the finished offset doesn't lay flat against a wall, strut, or floor — it rocks or stands off the surface. Usually an apprentice mistake: pipe rotated in the shoe between the first and second bend, or the bender wasn't held square on the second pull. Catch it by laying the pipe flat after both bends — if it rocks or one end lifts, you've got a dog leg.
Rim notch — center reference on some shoes, used for the middle bend of a 3-point saddle.
Multiplier — a fixed number per offset angle that converts offset depth → distance between bend marks. Mathematically, multiplier = cosecant of the angle.
Rise / Set — in a rolling offset, "rise" is the vertical component of the jog and "set" is the horizontal component.
Cosecant (csc) — the trig function behind the offset multipliers; csc(30°) = 2, csc(45°) ≈ 1.41, csc(22.5°) ≈ 2.61, csc(60°) ≈ 1.15.
Reference end — the end you measure from. Pick one at the start of the job and don't flip it mid-layout.
Bender Anatomy & Markings
Arrow — primary alignment mark on the shoe. Place your pencil mark on the arrow for stub-ups, offsets, saddle end-bends, and most simple pulls.
Star — back-of-bend reference, used mainly on the second bend of a back-to-back 90°. Not every brand has one; learn your bender.
Rim notch (or center mark) — center indicator on some shoes. Pairs with the middle mark on a 3-point saddle.
Deduct stamp — many benders have the take-up value stamped on the shoe for the size they're rated for (e.g. "5"" on a ½" EMT shoe). Factory value, trade-verified.
Handle — the leverage arm. Longer handles let you pull slower and smoother; jerky pulls twist the pipe out of plane. Keep your pull straight and steady.
Foot pedal / hook — where your weight goes. Step directly over the shoe, not off to the side, or the pipe rolls off-plane as you bend.
Shoe size — a ½" EMT shoe doesn't bend ¾" EMT without kinking the pipe. Check the size stamp on the shoe before you pull. Same goes for EMT vs. Rigid — the take-up is different.
Bender orientation — "arrow facing you" vs. "arrow facing away" flips the pull direction. If a measurement looks wrong, check which way you're pulling first.
Bend Types
90° Stub-Up
Mark = Stub Height − Take-up
Measure the height you want from the end of the conduit to the back of the bend. Subtract the take-up for your size and bender. Place the arrow of the bender on the mark; pull a full 90°.

Standard take-up values (hand bender):
 · ½" EMT → 5"
 · ¾" EMT → 6"
 · 1" EMT → 8"
 · 1¼" EMT → 11"

Rigid / IMC shoes cut the same sizes with slightly different take-ups (typically ~1" over EMT). Always verify against the stamp on your shoe — Klein, Ideal, Greenlee, and Gardner Bender can round differently.
Example: ½" EMT, stub height 14". Take-up is 5". Mark at 14 − 5 = 9" from the end. Arrow on the 9" mark; pull a full 90°.
Watch out: Using the take-up for the wrong size shoe; measuring stub from the wrong end of the pipe; under-pulling (the pipe springs back 2°–5° — pull a hair past 90°).
Back-to-Back
Mark 2 = Mark 1 + Distance Between Backs
First 90° is marked the normal way. For the second bend, measure from the back of the first bend to where you want the back of the second, and place the star (back-of-bend indicator) on that mark. Reverse the bender on the conduit for the second pull.
Example: ½" EMT, 36" back-to-back. Pull the first stub-up. From the back of that finished 90°, measure 36" and mark. Flip the bender (arrow facing the first bend now), align the star on the 36" mark, pull a full 90°.
Watch out: Forgetting to flip the bender on the second pull; using the arrow instead of the star (puts the back of the second bend in the wrong place); measuring second bend from the end of the pipe instead of the back of the first bend.
Offset Bend
Distance Between Marks = Offset × Multiplier
Used to jog around an obstacle. Pick an angle (common: 22.5°, 30°, 45°, 60°), multiply the offset depth by the multiplier for that angle, mark the two bend points that distance apart.

Multipliers — 10°: 6 · 22.5°: 2.6 · 30°: 2 · 45°: 1.4 · 60°: 1.15
Shrink per inch of offset — 10°: 1/16" · 22.5°: 3/16" · 30°: 1/4" · 45°: 3/8" · 60°: 1/2"

Shallower angles = less shrink + smoother pulls. Steeper angles = tighter jog in less space.
Example: 3" offset at 30°. Distance between marks = 3 × 2 = 6". Shrink = 3 × ¼" = ¾" — add to overall run length so the finished piece still lands where you need it. Pull 30° at the first mark, rotate the pipe flat to keep the second bend in the same plane, pull 30° at the second mark.
Watch out: Ignoring shrink — finished run comes out short. Rotating the pipe between bends (not keeping it flat) → offset comes out twisted. Using inconsistent angles on the two pulls → legs not parallel.
3-Point Saddle
Center Bend = 2 × End Bend Angle
Goes over a round obstruction (pipe, beam, conduit). Middle bend is double the angle of the two outer bends — most common combo is 45° center with 22.5° outers.

Distance from center to each end mark = Rise × multiplier for the end-bend angle (e.g. 2.6 for 22.5° outers).
Center mark = sits on the center of the obstacle + add the shrink.
Shrink ≈ Rise × 3/16" for a 45°/22.5° saddle.

Mark all three points on the conduit first, then bend center first, ends second — keeps the three bends in plane.
Example: 2" rise over a 1"-dia pipe, 45° center / 22.5° outers. End distances = 2 × 2.6 = 5.2" on each side of center. Shrink = 2 × 3/16 ≈ ⅜" — shift the center mark ⅜" toward your reference end so the saddle lands on the pipe.
Watch out: Bending the ends before the center → twisted saddle, out of plane. Skipping the shrink correction → saddle lands past the obstacle. Using a 30°/15° combo without recalculating the multipliers.
4-Point Saddle
= Offset In + Offset Out
Goes over a square-ish obstruction (a box, a beam web, another raceway). Treat as two offset bends back-to-back — an "up" offset followed by a matching "down" offset. Distance between the two inner bends = obstacle width + a small clearance. Each offset uses its own multiplier and contributes its own shrink.
Example: 2" rise over a 4" beam flange, 30° angles both sides. Each offset distance = 2 × 2 = 4" between its own marks. Inner marks (between the two offsets) = 4" flange + 1" clearance = 5" apart. Total shrink ≈ 2 × ¼" × 2 offsets = 1".
Watch out: Both offsets must be the same angle, or the finished run comes off non-parallel. Skipping the clearance margin → the saddle rests on top of the obstacle instead of clearing it. Forgetting to keep the pipe flat between the four pulls.
Rolling Offset (3D)
True Offset = √(Rise² + Set²)
For when a run has to jog both sideways and up/down between two points (common on parallel tray-to-panel drops). Treat the two jogs as legs of a right triangle:

True offset (hypotenuse) = √(Rise² + Set²)
Roll angle = arctan(Rise ÷ Set) — the angle you rotate the conduit in the bender so the offset comes out tilted the right way

Once you have the true offset, compute the bend marks exactly like a normal offset bend. Dry-fit before you cut to length.
Example: rise 6", set 8". True offset = √(36 + 64) = √100 = 10". Roll angle = arctan(6 ÷ 8) ≈ 36.87°. Treat 10" as the offset depth: at 30°, marks are 20" apart. Rotate the pipe 36.87° in the shoe before the second pull so the offset tilts into the rise/set direction you want.
Watch out: Getting the roll direction backward → pipe lands on the opposite side of where you need it. Measuring rise and set off wrong reference planes. Always dry-fit on the floor with tape before cutting to length.
Choosing Your Offset Angle
10° — nudge bends only. Marks are 6× the offset apart (a 3" offset = 18" between marks). Rarely useful on short runs; shines when you have real estate and just need a barely-there correction.
22.5° — parallel-set workhorse. Lowest shrink of the common angles (3/16" per inch), smoothest pulls, easiest on wire fill. Use on long pipe racks, low-ceiling runs, and any parallel set where shrink stacks.
30° — the default. Balanced distance-between-marks (2× offset), moderate shrink (¼" per inch), easy math. Use unless you have a reason not to.
45° — tight quarters. Distance between marks = 1.4× offset, shrink ⅜" per inch. Good when you need a quick jog in short space.
60° — very tight clearance, e.g. between stud bays, around compact junction boxes. Max shrink (½" per inch), steepest pull, highest strain on the pipe. Use only when space forces your hand.

Field decision shortcut: start at 30°. Go shallower (22.5° or 10°) if you have room and are worried about shrink or pull friction. Go steeper (45°/60°) only when the wall, rack, or obstacle forces you.
Parallel Runs & Same-Plane Bending
When multiple conduits run side-by-side on parallel centerlines and all need the same bend, the outer pipe travels a longer arc than the inner pipe. Mark every pipe identically and the outer ones come out short. Key idea: each successive pipe needs a slightly larger take-up — or a slightly larger distance between offset marks — to stay parallel after the bend.

Parallel 90° stub-ups ("wheeling") — when you want a row of stubs to land flush at the same face, each outer pipe's take-up grows by the center-to-center spacing. Example: ½" EMT parallel set, 4" center-to-center spacing. Inner pipe take-up 5". Next pipe out: 5" + 4" = 9". Next: 5" + 8" = 13". And so on. Mark each pipe with its own take-up, then bend.

Parallel offsets — when a group of conduits offsets together over the same obstacle, the outer pipes need their bend marks spaced slightly farther apart to stay parallel in the finished run. Rough rule: add (spacing × cos of the offset angle) to the distance between marks on each successive outer pipe. Always lay out on the floor first and confirm the geometry.

Parallel 3-point saddles — same idea, harder. Each pipe needs its own calculated center + end marks. Many journeymen build a simple layout template — one master pipe laid out perfectly, then transfer marks pipe-to-pipe with the spacing correction baked in. Saves re-doing the math six times in a 6-pipe rack.

Dry-fit everything. Parallel work rewards planning. Lay the run out on the floor, mark in chalk, and confirm before you cut or bend a single pipe. Real industrial pipe racks can have 8+ conduits going around the same obstacle — one misread turns into 8× the rework.

Same-plane rule: "same-plane" means all the bends stay in one flat plane — no twist. To hold plane on any multi-bend pipe, set the pipe flat on the floor after each pull and check that it lies without rocking. If it rocks, the last bend went off-plane.
Pro Tips (Field Wisdom)
Placeholder — Remy's 20-year journeyman voice goes here.

Good candidates for this section: which side of the bender arrow to put your mark on (and when that flips), how to square bends against a known-flat reference before the second pull, bending technique for tight quarters, which sizes cheat which way on deduction, cold-weather bending, PVC heating/forming, and the single field trick you wish your apprentice had learned first.
About SparkRef

SparkRef is an electrician's field calculator built by a union journeyman, for working electricians.

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SparkRef is a field calculator — not a substitute for official electrical code, AHJ review, or licensed-electrician judgment.

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SparkRef v1.0.0
Updated 2026-04-21