Based on the 2020 National Electric Code (NEC), the ampacity of the 6 AWG wire is as follows:

• 6 AWG Copper with 60°C insulation (like TW, UF): 55 Amps
• 6 AWG Copper with 75°C insulation (like RHW, THHW, THWN): 65 Amps
• 6 AWG Copper with 90°C insulation (like THHN, XHHW): 75 Amps

However, one thing that is crucial to note here is that even if a wire like THHN is rated for 90°C, most of the terminators you'll find on the market are rated either for 60°C or 75°C. Therefore, it is best to use 60°C or 75°C ampacity, even if you have 90°C wire.

Note that the ampacity of the wire can be reduced if the cable is bundled with other cables or is placed in high ambient temperatures. However, the regular ampacity of a 6 AWG copper wire that you are looking at in most installations is 55 to 65 amps. It can carry 55 amps, 60 amps, and 65 amps.

The ampacity of 6 AWG aluminum wire

The general guide on aluminum 6 AWG wire according to the National Electric Code (NEC) 2020 is as follows:

• 6 AWG Aluminum with 60°C insulation (like TW, UF): 40 Amps
• 6 AWG Aluminum with 75°C insulation (like RHW, THHW, THWN): 50 Amps
• 6 AWG Aluminum with 90°C insulation (like THHN, XHHW): 55 Amps

It is generally known that aluminum cables have lower ampacity than copper because of their lower electrical conductivity. Just like with copper wire, the point about the termination rating remains the same for aluminum wire. Even if the wire has a 90°C rating, you must use the ampacity corresponding to those ratings if the terminations are rated for 60°C or 75°C. Therefore, a common ampacity of a 6 AWG aluminum wire in practice is close to 40 - 50 amps.

Note on the ampacity of flexible cords like SOOW

Please note that the ampacity for flexible cords like SO cords is typically less than that for fixed wiring due to the cord's potential exposure to more adverse conditions, like coiling, that impact heat dissipation. As a general rule, a 6 AWG SOOW cord will be rated 45-55 amps max.

Common applications of 6 AWG cables

6 AWG cables are medium-duty cables for residential and commercial power distribution. Their most common applications include service entrances, subpanels, large appliances, and HVAC systems. They are also very commonly used for outbuilding electrical supply. Let's review some of the most common applications of these cables:

Service Entrance

6 AWG cables are common as service entrance cables for homes or small buildings for load requirements between 50 and 60 Amps.

Subpanels

6 AWG wire is commonly used to feed subpanels or secondary distribution panels in residential and commercial settings.

Large Appliances

This gauge suits large electrical appliances like ovens, stoves, and central air conditioning units.

HVAC Equipment

6 AWG cables are common for larger air conditioning units or HVAC equipment.

Well Pumps

6 AWG wire is a common choice for well pumps, especially if the distance from the power source is long and voltage drop can occur if using a lower gauge.

Temporary Power

6 AWG might be used on construction sites for temporary power distribution for tools and equipment.

Industrial Equipment

 This gauge might be used for machines and equipment with moderate power requirements in industrial settings. Some equipment that might work well with 6 AWG wires are motor feeders, air compressors, HVAC, and pumping systems.

Popular types of 6 AWG wire

1. THHN/THWN: These are primarily used in conduit for indoor applications. They can also be used for feeders and branch circuits. For example, they might run power from a main panel to an HVAC unit.
2. XHHW: This wire type is often found in conduits for both residential and commercial applications, especially when high heat resistance is required. Like THHN/THWN, it can be used for feeders and branch circuits. It is used in similar applications to THHN/THWN; it is just that the emphasis is on a higher heat resistance. 
3. USE-2: This is an underground service entrance wire. It is specifically designed to run from an external power source (like a pole or transformer) to the service equipment of a structure. 6 AWG USE-2 is commonly used for service entrance. 
4. UF-B: This cable is used for direct burial applications without a conduit. As a 6 AWG wire, UF is used for direct burial applications to bring power to medium-load outbuildings (like a workshop or detached garage) or for underground circuits powering things like landscape lighting or pond pumps.
5. SER: These are generally used as service entrance cables for homes or buildings. SER cables connect the main power supply to the interior distribution panel. When 6 AWG SER wire is used, it's typically for service entrance applications in smaller residential structures. This could connect the main power meter to a home's primary distribution panel.
6. RHW: 6 AWG RHH/RHW is for damp locations and is supposed to be located within conduit. This includes basements and locations exposed to moisture.
7. NM or Romex: 6 AWG Romex is used in interior residential wiring for large circuits in residential settings, such as powering outlets and switches for electric ovens and ranges.
8. MHF: 6 AWG MHF cables connect the main power source and the electrical system of the mobile home.
9. AC (Armored Cable) and MC (Metal Clad): 6 AWG armored cable is used for medium-load circuits in commercial buildings or other applications that require conduit protection. This post can help you choose whether you need an AC or MC cable.