If you are replacing a damaged male plug on a 120V power cord, the direct answer for standard US wiring is: the black (hot) wire lands on the brass screw, the white (neutral) wire lands on the silver screw, and the bare or green (ground) wire lands on the green screw. For a standard 15-amp circuit, use a minimum of 14 AWG wire (12 AWG preferred for heavy loads) and a plug rated for 15A/125V.
While many DIYers use the word "plug" to refer to the wall outlet, in electrical terminology, the plug is the male connector on the end of a cord (NEMA 5-15P), and the receptacle is the female wall outlet (NEMA 5-15R). This guide focuses on wiring the male replacement plug on a flexible cord, but the terminal color rules apply identically to both.
NEMA 5-15 Spec Sheet: Plug vs. Receptacle Terminal Mapping
Before stripping any wire, you need to understand the physical layout of the NEMA 5-15 standard. The National Electrical Code (NEC) Article 400 governs flexible cords, while Article 406 covers receptacles. Both mandate strict adherence to polarity and grounding. Use the table below as your bench reference to ensure every conductor lands on the correct terminal.
| Function | Wire Color (US/NEC) | Terminal / Screw Color | Physical Pin Shape (Male Plug) | Min. Wire Gauge (15A) |
|---|---|---|---|---|
| Hot (Line) | Black | Brass / Gold | Narrow Flat Blade | 14 AWG (12 AWG ideal) |
| Neutral | White | Silver | Wide Flat Blade | 14 AWG (12 AWG ideal) |
| Ground | Green or Bare Copper | Green | Round / U-Shape Pin | 14 AWG (12 AWG ideal) |
| Cord Jacket | Outer PVC/Rubber | Cord Grip / Clamp | Strain Relief Base | SOOW or SJTW type |
Source: Terminal mapping aligns with NFPA 70 (NEC) polarity requirements and OSHA 1910.305 flexible cord wiring standards.
Tools and Materials for a 15A Cord Plug
Do not use cheap, unlisted hardware store plugs for heavy-duty shop equipment. Invest in industrial-grade components that feature robust cord grips and high-quality brass terminals.
- Replacement Plug: Leviton 5266-C (15A/125V NEMA 5-15P) or Hubbell 5262. Both feature heavy-duty nylon bodies and reliable screw-terminal clamps.
- Flexible Cord: 14 AWG or 12 AWG, 3-conductor. Look for SOOW (heavy-duty rubber jacket, oil/water resistant) for shop tools, or SJTW (lighter PVC jacket) for general household extensions.
- Wire Strippers: Klein Tools 11063 (for 10-20 AWG) to ensure clean cuts without nicking the copper strands.
- Screwdrivers: Wiha insulated Phillips and flathead screwdrivers (rated 1000V) for safe termination.
- Multimeter: Fluke 117 or equivalent True-RMS meter for continuity and voltage verification.
- Utility Knife: For carefully slitting the outer cord jacket without scoring the inner conductor insulation.
Step-by-Step: How to Wire an Electric Plug (Male NEMA 5-15P)
- Prepare the Cord Jacket: Measure 1.5 inches from the end of the cord. Use your utility knife to carefully score the outer jacket around the circumference, then slit it lengthwise. Peel back the jacket and snip it off. Crucial: Do not nick the inner wire insulation. If you score the black, white, or green insulation, cut the cord and start over.
- Strip the Conductors: Using your wire strippers, strip exactly 3/4 inch of insulation off the ends of the black, white, and green/bare wires. Twist the exposed strands of each wire tightly clockwise to prevent fraying.
- Form the J-Hooks: Bend the bare copper ends of all three wires into a tight "J" shape or shepherd's hook. The hook should be sized to wrap snugly around the terminal screws.
- Terminate the Ground (Green/Bare): Loosen the green screw on the plug insert. Hook the green or bare wire around the green screw in a clockwise direction. Tighten the screw firmly. Clockwise wrapping ensures the screw pulls the loop tighter as it turns, rather than pushing the wire out.
- Terminate the Neutral (White): Loosen the silver screw. Hook the white wire around the silver screw clockwise. Tighten firmly. Ensure no bare copper is exposed outside the terminal clamp.
- Terminate the Hot (Black): Loosen the brass screw. Hook the black wire around the brass screw clockwise. Tighten firmly.
Torque Note: If you have a torque screwdriver, aim for 12-14 in-lbs. Otherwise, tighten until snug, then give it an additional 1/4 turn. Do not overtighten to the point of stripping the brass threads. - Secure the Cord Grip (Strain Relief): This is the most skipped step, and it is a massive safety hazard. The internal clamp or cord grip must bite down firmly on the thick outer rubber/PVC jacket of the cord, not on the individual colored wires. Adjust the cable insertion depth so the clamp sits squarely on the jacket. Tighten the clamp screws evenly.
- Reassemble the Housing: Slide the plug face into the outer rubber or nylon housing. Ensure no wires are pinched between the housing halves. Secure the housing with the central assembly screw.
The Most Common Botch: "Whiskers" and Thermal Failure
When learning how to wire an electric plug, the most frequent and dangerous mistake is leaving copper strand "whiskers" protruding from the terminal screws.
The Botch: A single stray strand of the black (hot) wire escapes the brass terminal and bridges the gap to the adjacent silver (neutral) screw or the metal cord grip.
The Symptom: The moment you plug the cord into a live wall receptacle, you will hear a violent "pop," see a flash, and the circuit breaker will instantly trip. You have created a dead short across the 120V line. In severe cases, this can melt the plug face or cause arc-flash burns to your hands.
The Fix: Before closing the plug housing, visually inspect every terminal. Tug gently on each wire to ensure it is seated. Use flush cutters to snip any stray whiskers. If a wire looks messy or frayed, unscrew it, snip the end clean, re-twist, and terminate it again.
Secondary Botch (Thermal Failure): Failing to clamp the cord grip over the outer jacket. If the grip only holds the inner wires, the weight of the tool or a slight tug will pull the live black wire directly out of the brass terminal, leaving exposed, energized copper inside the plug housing. Always verify the grip is crushing the outer jacket.
Verify and Test: Expected Multimeter Readings
Never use the "plug it in and see if it sparks" method. You must verify your wiring with a multimeter in two distinct phases: a dead continuity test, followed by a live voltage test.
Phase 1: Dead Continuity Test (Unplugged)
Set your multimeter to the Continuity or Ohms (Ω) setting. Place one probe on the male plug's narrow brass blade (Hot) and the other on the wide silver blade (Neutral).
- Expected Reading: OL (Open Line) or infinite resistance. If you read near 0 Ω, you have a dead short. Do not plug it in. Open the plug and find the stray whisker.
- Repeat between Hot (narrow blade) and Ground (round pin). Expected: OL.
- Repeat between Neutral (wide blade) and Ground (round pin). Expected: OL.
Phase 2: Live Voltage Test (Plugged In)
Once continuity tests pass, plug the cord into a known-good 120V GFCI-protected receptacle. Set your multimeter to AC Voltage (V~). Carefully insert the probes into the female end of the cord (or test the exposed blades at the male end if testing a pigtail, though testing the female end is safer).
- Hot to Neutral: Insert the red probe into the narrow slot (Hot) and black probe into the wide slot (Neutral). Expected reading: 114V to 126V AC.
- Hot to Ground: Red probe to narrow slot, black probe to the round U-shaped ground hole. Expected reading: 114V to 126V AC.
- Neutral to Ground: Red probe to wide slot, black probe to round hole. Expected reading: 0V to 2V AC. (A reading higher than 2V indicates a loose neutral connection or a shared neutral issue upstream).
If all readings match these thresholds, your plug is wired correctly, polarized, and safely grounded. You can now put the cord into service.
