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An extension-cord size chart matches a tool’s nameplate amperage to the total cord length so you can choose an adequate wire gauge. For a 100-foot run, for example, a 10-amp tool falls in the cited chart’s 7.1–12.0-amp row and calls for 10 AWG; a 15-amp tool has no value in that chart at 100 feet, so you must not guess or extrapolate. Lower AWG numbers mean thicker conductors, and a longer run or larger load generally requires a heavier (lower-number) gauge.
Use the chart as a manufacturer example, then verify the actual cord’s current and voltage rating, grounding, jacket designation and the tool manufacturer’s instructions. The Milwaukee extension-cord chart is based on limiting line-voltage drop to five volts at 150% of rated amperes; it is not a universal ampacity table for every cord construction or job condition.
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Read the tool or appliance nameplate first, determine the complete cord length from the receptacle to the equipment, and use the intersection of amperage and length. Then confirm that the selected cord’s own listing permits the load and environment. Follow these steps:
- Find the nameplate amperage. Use the running amperes printed on the tool. If one cord supplies more than one tool at the same time, add the nameplate amperages as directed in the cited tool manual.
- Measure the total one-way length. Include every foot from the supply outlet to the tool; do not count only the part lying on the floor.
- Locate the chart row and length column. Select the listed AWG value where they meet. A lower AWG number is a thicker wire with greater capacity.
- Check the product label and instructions. Confirm voltage, amperage, grounding, conductor count, indoor or outdoor rating and any special limits. A chart cannot override a cord or tool’s marked rating.
- Use the shortest practical cord. If the exact distance is between columns, use the next longer column rather than treating a shorter length as equivalent.
The chart below reproduces the values in Milwaukee Electric Tool Corporation manual catalog no. 6020-21. A dash means the source supplies no value for that combination; it is not permission to estimate a gauge.
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What does the extension-cord size chart say?
| Nameplate amperes | 25 ft | 50 ft | 75 ft | 100 ft | 150 ft |
|---|---|---|---|---|---|
| 0–2.0 | 18 AWG | 18 AWG | 18 AWG | 18 AWG | 16 AWG |
| 2.1–3.4 | 18 AWG | 18 AWG | 18 AWG | 16 AWG | 14 AWG |
| 3.5–5.0 | 18 AWG | 18 AWG | 16 AWG | 14 AWG | 12 AWG |
| 5.1–7.0 | 18 AWG | 16 AWG | 14 AWG | 12 AWG | 12 AWG |
| 7.1–12.0 | 16 AWG | 14 AWG | 12 AWG | 10 AWG | — |
| 12.1–16.0 | 14 AWG | 12 AWG | 10 AWG | — | — |
| 16.1–20.0 | 12 AWG | 10 AWG | — | — | — |
For example, a 10-amp tool on a 100-foot run lands in the 7.1–12.0-amp row and lists 10 AWG. A 15-amp tool on the same run lands in the 12.1–16.0-amp row, where the chart is blank. The safe response is to consult the tool and cord manufacturers or redesign the setup, not to infer that 12 or 14 AWG will work.
Does a lower or higher AWG number mean a thicker wire?
A lower American Wire Gauge (AWG) number means a larger, thicker copper conductor. An 18-AWG conductor is smaller than 16 AWG; 12 AWG is larger than either. Because resistance rises as a conductor gets smaller and as the circuit gets longer, the chart moves toward lower AWG numbers when amperage or distance increases.
The OSHA construction electrical-hazards workbook gives rough examples: 18 AWG is typical of lamp cords; 16 AWG is common for general-purpose items such as work lights and electric trimmers but is not intended for high-power loads or recommended for construction work; 14 AWG is the minimum size it recommends for construction work; 12 AWG suits heavy use such as large power tools; and 10 AWG is used for large loads. Those are orientation examples, not a substitute for the exact cord listing, length and equipment instructions.
Why does a longer extension cord need a heavier gauge?
Current flowing through a long conductor creates voltage drop. The farther the tool is from the receptacle, the more voltage is lost in the cord, which can reduce motor power, increase heating and contribute to tool damage. Milwaukee’s manual states, “As the distance from the supply outlet increases, you must use a heavier gauge extension cord.”
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The chart’s five-volt limit is a design assumption for that particular manufacturer guidance, not a guarantee that every cord installation will behave identically. Coiled cords, elevated ambient temperatures, multiple connected loads and receptacle or supply-circuit limitations can change actual performance. Keep the cord fully uncoiled when the product instructions require it, and never use a chart cell that the source leaves blank.
What gauge is needed for a 100-foot extension-cord run?
There is no single 100-foot answer because amperage still controls the choice. In the cited chart, 5.1–7.0 amps calls for 12 AWG at 100 feet, while 7.1–12.0 amps calls for 10 AWG. The 12.1–16.0-amp row has no 100-foot entry, so a 15-amp tool requires manufacturer-specific guidance rather than extrapolation.
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What do markings such as 14/3 and W mean?
A marking such as 14/3 identifies 14-AWG conductors and three conductors in the cord. Three-conductor cords normally provide hot, neutral and an equipment-grounding conductor for grounded tools; the tool and cord plugs must be compatible. Gauge alone does not tell you whether a cord is grounded or suitable for a particular environment.
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In the cord-lettering scheme described by OSHA, W indicates moisture and sunlight resistance. Product suffixes vary by standard and manufacturer: Milwaukee’s applicable guidance calls for a W-A suffix (or W in Canada) for outdoor cords. Read the complete jacket marking and the manufacturer’s specifications instead of inferring suitability from one letter.
How do you choose an indoor or outdoor extension cord?
Use an outdoor-rated cord outdoors; an outdoor-rated cord can also be used indoors, but an indoor-only cord should not be taken outside. Outdoor cords generally have a jacket designed to withstand moisture and sunlight, while indoor cords may not.
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Inspect the cord before every use. The UC San Diego Environmental Health and Safety guidance advises replacing cords with cracked or frayed insulation rather than taping them, avoiding daisy-chaining, and not routing cords under carpeting or through walls. Keep connectors out of standing water, protect them from vehicle traffic and sharp edges, and unplug the cord before moving or inspecting equipment.
Grounding is equally important. Grounded tools require a three-wire extension cord, and the grounding pin should never be removed to fit a two-slot receptacle. OSHA’s workbook quotes the applicable construction rule: “Extension cord sets used with portable tools and appliances must be of the three-wire, grounding type; and flexible cords must be designed for hard or extra-hard usage.” Follow the requirements for your jurisdiction and worksite, including any ground-fault protection required by the installation.
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What safety characteristics should an extension cord have?
The U.S. Consumer Product Safety Commission’s extension-cord FAQ identifies several observable characteristics that reduce shock and fire risk: minimum wire size, sufficient strain relief, proper polarization and proper continuity. It also discusses outlet covers for two-wire indoor cords and jacketed construction for outdoor cords. The Commission describes a cord lacking applicable characteristics as a substantial product hazard.
That CPSC rule applies to specified household cord sets and does not cover every item consumers casually call an extension cord, including power strips and some nonstandard cord sets. Therefore, check the exact product category, listing marks and instructions. A cord can have an adequate AWG yet still be unsuitable because its plug, grounding, strain relief, jacket or voltage rating is wrong.
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Unplug the equipment and investigate instead of continuing to operate it. A long, undersized cord can produce voltage drop that feels like weak motor performance; a damaged connector, overloaded receptacle circuit or failing tool can create similar symptoms. Check the nameplate amperage, total length and chart row, then inspect the cord for cuts, crushed sections, discoloration, loose blades or a hot plug.
Replace a damaged cord; do not make field repairs with tape or improvised splices. If the correct chart cell is blank, if the cord’s rating is lower than the load, or if overheating persists with a correctly selected cord, stop using the setup and have the circuit or equipment evaluated by a qualified electrician.
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Extension-cord selection checklist
- Record each tool’s nameplate amperage, voltage and whether it requires grounding.
- Measure the complete one-way distance and choose the shortest practical length.
- Use a manufacturer chart or the tool manual that covers the load and distance; select the next heavier gauge when between entries.
- Verify the cord’s marked amperage and voltage ratings, conductor count and plug configuration.
- Choose an outdoor-rated, moisture- and sunlight-resistant jacket for outdoor work.
- Look for intact insulation, strain relief, polarization and continuity; discard damaged cords.
- Do not daisy-chain cords, hide them under rugs or run them through walls.
- Keep grounded tools on three-wire cords and preserve the grounding path.
- Do not extrapolate into a dash or blank chart cell; obtain manufacturer guidance.
How we picked the chart and recommendations
The table uses the published Milwaukee values because they provide explicit amperage and length intersections and state their voltage-drop assumption. Safety guidance is cross-checked against OSHA’s gauge and grounding explanations, UC San Diego’s use and inspection practices, and CPSC’s product-safety characteristics. The recommendations prioritize the actual load, total distance, cord rating, grounding and environmental jacket rather than treating AWG as an all-purpose amp rating.
Frequently Asked Questions
Can an outdoor-rated extension cord be used indoors?
Yes. UC San Diego’s guidance allows an outdoor-rated cord indoors, provided its plug, rating and condition suit the equipment. The reverse is not acceptable: an indoor-only cord should not be used outside.
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Does 14/3 tell me how many amps a cord can carry?
No. The marking identifies conductor size and count, not a universal amp limit. Length, insulation, temperature rating, product construction and the manufacturer’s marked current and voltage ratings determine suitability.
Why are some amperage-and-length cells blank on the chart?
The manufacturer did not provide a recommendation for those combinations under its stated voltage-drop method. Treat a blank as a stop sign and obtain instructions for the exact tool and cord instead of calculating a thinner gauge from neighboring cells.
Is a 12-gauge, 100-foot cord automatically safe for a 15-amp tool?
No. The cited chart lists 12 AWG at 100 feet for 5.1–7.0 amps but gives no 100-foot value for 12.1–16.0 amps. A 15-amp tool therefore needs a manufacturer-approved solution, such as a different length, cord design or power arrangement.
