Use this calculator to help select the correct wire size.

  You should never use a wire that is not suitable for the amperage that it will carry. The wire might possibly melt in a worse case scenario or overheat.

  However keep in mind that an outlet or receptacle rated for 50 Amps, doesn't mean that the equipment connected to that outlet requires 50 Amps.

Likewise simply because an appliance or device features a 6-50P or 14-50P plug doesn't mean that it will be drawing 50 Amps. 

  Inrush current, or switch-on surge is the maximal instantaneous input current drawn by an electrical device when first turned on. Alternating-current electric motors and transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform, then level out drawing significantly less. 

•  Terms such as "Heavy Duty" and "Contractor Grade" are often used in product descriptions of electrical cords.
• The terms have no universal definition.
• Do not just buy an extension cord simply because the packaging states it's HEAVY DUTY and rated for INDOOR and OUTDOOR use.
• "Heavy Duty" is often used to describe 8/4 SEOOW Portable Cable but the term is just as likely to be used to describe 12/3 SJT Extension Cords. However there is a significant difference between those two cables. 

Ampacity refers to the maximum current (measured in amperes or simply amps) that an insulated conductor can safely carry without exceeding its insulation and jacket temperature limitations. As current flows through a conductor, it generates heat. This heat must dissipate into the environment; otherwise, the cable’s temperature would rise above safe operating limits, leading to deterioration and potential failure.

Wire gauge directly determines a "wire's" rated amperage (ampacity) because it dictates the size of the conductor and its ability to dissipate heat, with thicker wires (lower AWG numbers) handling more current. 

The ampacity of a cable should equal or exceed the maximum current it will carry during its service life without surpassing its temperature rating. The temperature rating depends on the heat resistance of the insulation and jacket materials. Common conductor temperature ratings include 90°C, 150°C and 200°C, but some special-purpose wires can handle temperatures as high as 1,200°C1.

The wires insulation's temperature rating influences the wire's ampacity for the conductor; higher temperature-rated insulation allows for a higher ampacity for the same wire gauge. As seen when comparing 60°C and 90°C rated wires. 

A 14-gauge wire might support 15 amps, a 12-gauge supports 20 amps, and a 10-gauge supports 30 amps, but these ratings are adjusted by the insulation type. Rated amps can vary significantly based on different manufacturers variances, manufacturers might also calculate rated differently 

Examples:

For the same 10-gauge wire, the ampacity can increase from 30 amps with 60°C insulation to 40 amps with 90°C insulation

Derating Factors 

Several factors impact ampacity, including ambient temperatures and the number of current-carrying conductors. Here are key considerations: 

Ambient Temperature: The rate at which heat dissipates depends on the installation environment. Heat radiates out of the cable less effectively as the ambient temperature rises. To ensure we do not exceed the cable's temperature rating, a correction factor is applied to the ampacity rating. As the ambient temperature rises, correction factors reduce the cable ampacity value. 

Number of Conductors: More conductors in an enclosed space can lead to a higher ambient temperature environment. Derating compensates for this increase in heat. If more than three current-carrying conductors are in a raceway or cable, the ampacity ratings must be derated according to NEC requirements. 

Conductor Material: The material of the conductor (e.g., copper or aluminum) also affects its resistance and, therefore, its ampacity. 

Installation Method: Bundling wires in conduit or in close proximity can restrict heat dissipation, requiring derating of the cable's current capacity. 

Duty Cycle: Continuous current flow generates more heat than intermittent current, affecting the cable's ampacity. 

A home refrigerator's power consumption is typically between 300 to 800 watts of electricity, or between 3 and 6 amps and about 120 volts. Importantly, refrigerators generally have a much lower "running" wattage than their stated average wattage – this is because they cycle on and off throughout the day.

Small window AC units (5,000 to 8,000 BTU) typically use 5 to 7 amps. Medium window AC units (10,000 to 12,000 BTU) often use between 8 to 12 amps. Large window AC units (14,000 to 25,000 BTU) can use anywhere from 12 to 20 amps or more.

Central air conditioners typically require higher air conditioner amperage due to their larger cooling capacity. A 2-ton central AC unit may draw around 15-20 amps. A 3.5-ton unit may require 25-30 amps. A 5-ton unit may need 30-40 amps.