Extension Cord Wire Gauge and Voltage Drop Checklist
Quick answer
Choose a listed grounded cord rated for at least the equipment current, then account for total length and voltage drop; lower AWG numbers mean larger conductors. For high-current, continuous, motor, heater, wet-location, or long-run use, follow the equipment manual and use a shorter/heavier cord—or a permanent receptacle—rather than relying on a rule-of-thumb chart.
Source note: Reviewed using OSHA and CPSC extension-cord guidance in August 2026. The table is a conservative planning screen, not a substitute for product instructions or code.
Extension cords are temporary wiring. Start with the equipment nameplate and manual, choose a listed cord rated for the location and load, keep it as short as practical, and uncoil it fully. A cord that feels hot, has damaged insulation, loose blades, discolouration, or a missing ground pin must be removed from service.
Planning screen by load and one-way length
This conservative table is for ordinary 120 V copper extension cords in good condition. It does not approve a cord for an appliance whose manual prohibits extension cords.
| Load | Up to 25 ft | 26–50 ft | 51–100 ft | Beyond 100 ft |
|---|---|---|---|---|
| Up to 5 A | 16 AWG | 16 AWG | 14 AWG | Prefer a closer receptacle |
| 5–10 A | 16 AWG | 14 AWG | 12 AWG | Calculate drop/use temporary power |
| 10–13 A | 14 AWG | 12 AWG | 10 AWG | Prefer a closer receptacle |
| 13–15 A | 12 AWG | 10 AWG | Avoid unless manufacturer permits and sizing is engineered | Install suitable power |
Lower AWG numbers are thicker. The cord’s printed ampere/watt rating, temperature rating, and product instructions override the table. Never use a 15 A cord on a 20 A load merely because the wall circuit is 20 A.
Five-step checklist
- Read the load. Use nameplate running amps/watts and account for motor starting current. For watts on 120 V, approximate current as watts ÷ 120, but use manufacturer data when available.
- Measure the whole route. Chaining two 50 ft cords creates a 100 ft run plus an extra vulnerable connection. Avoid daisy chains.
- Match the environment. Outdoors or in damp locations, use cords specifically listed for that use and GFCI protection where required. Keep connections out of water.
- Protect the cord physically. Do not run it through walls, ceilings, doors, under rugs, across sharp edges, or where vehicles can crush it.
- Check during operation. Stop if the plug, connector, or cable becomes hot, power fluctuates, a motor struggles, or protection trips.
Why voltage drop matters
Every conductor has resistance. The outgoing and return path make the electrical loop roughly twice the one-way cord length. As current and resistance rise, voltage at the equipment falls and the cord dissipates more heat. Motors may start slowly or draw abnormal current; heaters may underperform while connections still overheat.
Do not solve a tripping breaker with a heavier cord alone—the appliance, circuit, or connection may have a fault. See the breaker trip safety check. For permanent conductor selection, the wire gauge and ampacity guide explains why building wiring uses additional code factors. For generators, use the generator sizing guide and the exact generator receptacle/manual requirements.
Loads that deserve extra caution
Portable heaters, air conditioners, welders, EV charging equipment, pumps, compressors, and large kitchen appliances often have high or continuous current and may prohibit extension cords. A cord is not a substitute for a correctly installed circuit. Never use an indoor cord for a generator; operate generators outdoors away from windows and doors.
OSHA’s portable electric equipment guidance requires visual inspection and removal of damaged equipment from service in workplaces. CPSC provides broader home electrical safety information. Product listings, workplace rules, and local code determine the final choice.
Amperage HQ Editorial Team
Independent trade-focused editorial team