— Wiring/Cable
Wire Gauge (AWG) & Ampacity
"Chassis Wiring" assumes a single conductor in free air over a short run (e.g. instrument/panel wiring), "Power Trans." is a conservative rating for longer runs, and "60/75/90°C" columns are code-mandated ampacity.
| AWG | Cir. Mils | 60°C | 75°C | 90°C | Chassis Wiring | Power Trans. |
|---|---|---|---|---|---|---|
| 4/0 | 211,600 | 195 A | 230 A | 260 A | 380 A | 302 A |
| 3/0 | 167,800 | 165 A | 200 A | 225 A | 328 A | 239 A |
| 2/0 | 133,100 | 145 A | 175 A | 195 A | 283 A | 190 A |
| 1/0 | 105,600 | 125 A | 150 A | 170 A | 245 A | 150 A |
| 1 | 83,690 | 110 A | 130 A | 150 A | 211 A | 119 A |
| 2 | 66,360 | 95 A | 115 A | 130 A | 181 A | 94 A |
| 3 | 52,620 | 85 A | 100 A | 110 A | 158 A | 75 A |
| 4 | 41,740 | 70 A | 85 A | 95 A | 135 A | 60 A |
| 6 | 26,240 | 55 A | 65 A | 75 A | 101 A | 37 A |
| 8 | 16,510 | 40 A | 50 A | 55 A | 73 A | 24 A |
| 10 | 10,380 | 30 A | 35 A | 40 A | 55 A | 15 A |
| 12 | 6,530 | 20 A | 25 A | 30 A | 41 A | 9.3 A |
| 14 | 4,110 | 15 A | 20 A | 25 A | 32 A | 5.9 A |
| 16 | 2,583 | — | — | — | 22 A | 3.7 A |
| 18 | 1,624 | — | — | — | 16 A | 2.3 A |
| 20 | 1,022 | — | — | — | 11 A | 1.5 A |
| 22 | 642.4 | — | — | — | 7 A | 0.92 A |
| 24 | 404.0 | — | — | — | 3.5 A | 0.577 A |
| 26 | 254.1 | — | — | — | 2.2 A | 0.361 A |
| 28 | 159.8 | — | — | — | 1.4 A | 0.226 A |
| 30 | 100.5 | — | — | — | 0.86 A | 0.142 A |
See the Wire/Cable Sizing & Voltage Drop calculator to size a run against both ampacity and a target voltage drop.
Insulation Types & Temperature Ratings
| Type | Max Temperature | Typical Use |
|---|---|---|
| PVC (general purpose) | 60–75°C | Low-cost general wiring, appliance cords |
| THHN/THWN-2 | 90°C dry / 75°C wet | Most common building/machine tool wire |
| XHHW-2 (XLPE) | 90°C dry & wet | Building wire; better moisture resistance than PVC |
| Silicone rubber | 200°C+ | High-flex leads, motor/appliance internal wiring |
| ETFE (Tefzel) | 150°C | Lightweight aerospace/mil-spec wiring |
| PTFE (Teflon) | 200–260°C | High-temp aerospace/military, chemical resistance |
| Polyimide (Kapton) film | 220°C+ | Extreme-temp wiring, motor windings, aerospace |
Crimp & Terminal Types
| Type | Description | Typical Use |
|---|---|---|
| Ring terminal | Closed loop, bolts to a stud — can't slip off | Battery terminals, permanent ground/power connections |
| Spade/fork terminal | Open U-shape slides under a loosened screw | Terminal blocks, points needing quick access |
| Quick-disconnect (blade) | Push-on male/female flat blade pair | Automotive and appliance quick-connects |
| Butt splice | Joins two wire ends in-line | Wire repair, extending a run |
| Ferrule | Tubular sleeve crimped onto stripped stranded wire | Clean, solid termination into a terminal block |
| Pin/socket contact | Individual crimp contact seated in a connector housing | Multi-circuit disconnects (e.g. Molex, Deutsch) |
Insulated terminal color coding by wire gauge, per MIL-DTL-7928 convention: Red = 22–16 AWG, Blue = 16–14 AWG, Yellow = 12–10 AWG.
Wire Callout on a Schematic/Harness Drawing
A wire on a harness or interconnect drawing is called out with its circuit/net identifier, gauge, insulation spec, and color (base color, or base/stripe for a striped wire), per IPC/WHMA-A-620, Requirements and Acceptance for Cable and Wire Harness Assemblies.
W12 = circuit/net ID from the wiring diagram · 20 AWG = gauge · PTFE = insulation type (or a full spec number, e.g. M22759/16) · WHT/RED = base color with a stripe color, for tracing the wire back to its net on a populated harness.
Circuit Protection
| Fuse Type | Response | Typical Use |
|---|---|---|
| Fast-blow | Opens within milliseconds once current exceeds rating, no intentional delay | Semiconductor/electronic protection, resistive loads with no surge |
| Slow-blow (time-delay) | Absorbs short overcurrent spikes by design, opens only if overload is sustained | Motors, transformers, capacitor-input supplies — anything with startup inrush |
| Resettable (PTC/polyfuse) | Resistance rises sharply at the trip point and resets automatically once power is removed and it cools | Battery packs, USB/port protection, low-voltage circuits needing auto-recovery |
| Glass cartridge (3AG/5×20mm) | Fast or slow-blow variants; lower breaking capacity | Low-voltage electronics, instrument panels |
| Ceramic cartridge | Same sizes as glass, higher breaking capacity (ceramic body/filler contains the arc) | Mains-connected circuits where the fuse must safely clear a hard short |
| Automotive blade (ATO/ATC, Mini, Micro2) | Fast-acting, calibrated to SAE/ISO blow-time curves | 12/24V automotive and DC power distribution |
| Breaker Type | Detects | Typical Application |
|---|---|---|
| Thermal | Sustained overload (heat buildup) — inverse-time bimetallic trip | Standalone overload protection, often paired with separate short-circuit protection |
| Magnetic | Short circuit / high fault current — near-instantaneous trip | Standalone short-circuit (instantaneous) protection |
| Thermal-magnetic | Both overload (thermal) and short circuit (magnetic, ~10–20× rated current) | General-purpose branch circuit breakers — the most common type |
| GFCI (ground-fault) | Line-to-ground current imbalance, ~5–6 mA | NEC-mandated for bathrooms, kitchens, garages, outdoor/wet locations (Art. 210.8) |
| AFCI (arc-fault) | Waveform signatures of series/parallel arcing faults | NEC-mandated for most dwelling-unit living spaces (Art. 210.12) |
NEC Table 310.15(B)(1) — ampacity correction factors for ambient temperature other than the 30°C (86°F) base used in the standard ampacity tables:
| Ambient °C (°F) | 60°C Col. | 75°C Col. | 90°C Col. |
|---|---|---|---|
| 21–25 (70–77) | 1.08 | 1.05 | 1.04 |
| 26–30 (78–86) | 1.00 | 1.00 | 1.00 |
| 31–35 (87–95) | 0.91 | 0.94 | 0.96 |
| 36–40 (96–104) | 0.82 | 0.88 | 0.91 |
| 41–45 (105–113) | 0.71 | 0.82 | 0.87 |
| 46–50 (114–122) | 0.58 | 0.75 | 0.82 |
| 51–55 (123–131) | 0.41 | 0.67 | 0.76 |
| 56–60 (132–140) | — | 0.58 | 0.71 |
| 61–65 (141–149) | — | 0.47 | 0.65 |
| 66–70 (150–158) | — | 0.33 | 0.58 |
| 71–75 (159–167) | — | — | 0.50 |
NEC Table 310.15(C)(1) — adjustment factors for more than 3 current-carrying conductors in a single raceway, cable, or bundle:
| Conductors | % of Table 310.16 Ampacity |
|---|---|
| 4–6 | 80% |
| 7–9 | 70% |
| 10–20 | 50% |
| 21–30 | 45% |
| 31–40 | 40% |
| 41+ | 35% |
See the Circuit Breaker/Fuse Sizing calculator to size a device from a load current.