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Technical Guide

Wire Gauge Selection Guide for Power Cords

Ampacity tables, the 80% continuous load rule, temperature derating, and real-world guidance for selecting the right AWG for data center and industrial power cord applications.

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By World Cord Sets Engineering Team · Updated May 2026

The 80% rule — the most important thing to know

The NEC (National Electrical Code) requires that continuous loads — any load expected to run for 3 or more consecutive hours — not exceed 80% of the circuit's rated ampacity. Data center equipment is almost always continuous load by this definition.

This means: an 18 AWG cord rated at 10A should carry no more than 8A on a continuous basis. A server drawing 8.5A exceeds that limit and the cord will run hotter than designed over time.

Most power cord specifications you see in catalogs are maximum rated ampacity at 25°C ambient — not continuous capacity in a hot aisle. The practical capacity is meaningfully lower.

AWG ampacity table for power cords

Continuous capacity = rated ampacity × 0.80 × ambient temperature correction factor.

GaugeIEC equiv.Max ratedContinuous (25°C)Continuous (40°C)Applications
18 AWG0.75 mm²10A7A5.7ALight-duty: traditional servers <300W, consumer electronics, small office equipment. NOT suitable for continuous loads above 7A. Connectors: C13/C14, C7/C8.
16 AWG1.5 mm²13A10A8.2AMedium loads: modern 500–800W servers at normal ambient. Not recommended for hot aisles above 35°C with loads over 8A. Connectors: C13/C14, C15/C16.
14 AWG2.5 mm²15A12A9.8AStandard for data center applications. Correct choice for most 10A and below continuous loads in hot aisles. Minimum for C19/C20 at rated ampacity. Connectors: C13/C14, C15/C16, C19/C20.
12 AWG4.0 mm²20A16A13.1AHigh-current applications: C19/C20 cords for AI servers at rated 16A, hot aisle applications above 40°C. Required for Saf-D-Grid 30A connections. Connectors: C19/C20, C21/C22.
10 AWG6.0 mm²30A24A19.7AIndustrial and high-current data center feeds. IEC 60309 connections, PDU input feeds, generator connections. Rarely used for individual server connections. Connectors: IEC 60309.

Continuous capacity = rated ampacity × 0.80 × NEC correction factor. 40°C correction factor = 0.82 for 60°C-rated conductors. Consult full NEC Table 310.15 for your specific ambient temperature.

Calculate the right gauge for your specific load and environment.

Free calculator — enter voltage, current, ambient temperature, and run length. Open the calculator →

FAQ

Frequently asked questions

Still unsure which gauge fits your application? Call (860) 763-2100 and an engineer will help you spec it.

What wire gauge should I use for a 15A power cord?
14 AWG is the right choice for a 15A continuous load in a normal ambient environment. 16 AWG is rated 13A (after the 80% continuous rule), which is marginal. For hot aisle applications above 35°C, 14 AWG provides meaningful safety margin that 16 AWG does not.
What is the difference between 18 AWG, 16 AWG, and 14 AWG power cords?
18 AWG is rated for 10A maximum (7A continuous at 25°C ambient). 16 AWG is rated 13A (10A continuous). 14 AWG is rated 15A (12A continuous). Larger AWG numbers mean thinner wire — counterintuitively, 18 AWG is thinner than 14 AWG.
What happens if you use an undersized wire gauge?
An undersized conductor runs hot. Over time, this degrades the insulation, increases contact resistance, and creates a fire risk. In a data center running continuously at 95% load, an 18 AWG cord in a 40°C hot aisle will fail years before the same cord would fail in a climate-controlled office.
What AWG do C19/C20 power cords use?
Most C19/C20 cords use 14 AWG conductors. For 16A continuous loads, 12 AWG provides a larger safety margin. For Saf-D-Grid (30A) connections, 12 AWG minimum is required.
What does AWG mean?
AWG stands for American Wire Gauge. It's an inverse scale — smaller AWG numbers mean thicker wire with higher ampacity. 10 AWG is thicker and can carry more current than 18 AWG. The IEC equivalent is cross-sectional area in mm²: 18 AWG ≈ 0.75 mm², 14 AWG ≈ 2.5 mm².
What is the difference between SJT and SVT power cord jackets?

SJT (Service Junior Thermoplastic) is a hard-service jacket rated for commercial and data center use, including continuous loads and environments where the cord may be subject to physical stress.

SVT (Vacuum Thermoplastic) is a light-duty jacket intended for small consumer appliances. It is not permitted for hard-service or continuous commercial applications under UL or NEC rules.

For data center power cords and PDU connections, SJT is the correct choice. SVT should not be substituted even if the wire gauge matches.

What are the specifications for an SJT power cord?

An SJT cord is a UL-listed, hard-service thermoplastic-jacketed cord. Key characteristics include:

  • Rated for hard service (pendant and portable use)
  • Thermoplastic insulation and outer jacket
  • Available in 18 AWG, 16 AWG, 14 AWG, and 12 AWG conductors
  • Suitable for continuous commercial and data center loads when paired with the correct wire gauge

The 'J' in SJT denotes junior hard service (300V rating); cords without the 'J' (e.g., ST) are rated for 600V heavy hard service.

Can I use an SVT cord in a data center or for continuous commercial loads?

No. SVT is a light-duty designation restricted to small appliances and similar consumer equipment. It is not permitted for hard-service, continuous commercial, or data center applications under UL standards and the NEC.

Using an SVT cord in a data center — even with the correct wire gauge — may constitute a code violation and can void equipment warranties. Always specify SJT or heavier for commercial and data center power cord applications.

SJT vs SVT Power Cord Jackets: Which Do You Need?

The jacket type printed on a power cord — SJT, SVT, SJTW, and others — is a UL designation that defines the cord's construction, flexibility, and permitted applications. Choosing the wrong jacket can create a code violation even when the wire gauge is correct.

SJT (Service Junior Thermoplastic)

SJT is the standard jacket for most data center and commercial power cords. It is rated for hard service use, meaning it can be used in areas where the cord may be subject to physical abuse, repeated flexing, or higher ambient temperatures. SJT cords are permitted in both pendant and portable applications.

SVT (Vacuum Thermoplastic)

SVT is a light-duty designation intended for small appliances, vacuum cleaners, and similar consumer equipment. SVT cords are not permitted for hard service or data center use. They are thinner, more flexible, and lower cost — but they carry a lower ampacity rating and are restricted to specific applications by UL and the NEC.

Key differences at a glance

  • SJT: Hard service, data center and commercial permitted, heavier construction.
  • SVT: Light duty, consumer appliances only, not suitable for continuous commercial loads.
  • SJTW: Same as SJT with added weather resistance for outdoor or damp locations.

For data center PDU connections, server power cords, and any continuous-load application, SJT is the correct jacket type. SVT should not be substituted even if the wire gauge is identical.

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