Wire Gauge (AWG), Ampacity & Derating
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) |
See the Circuit Breaker/Fuse Sizing calculator to size a device from a load current.