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What is the Suitable Wire Size for 20A Breaker and Outlet?

Electrical Technology
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How to Find the the Right Wire Size for a 20-Amp Breaker and Outlet Based on NEC?

Choosing the the suitable wire size for a 20-ampere (20A) breaker and outlet is important for safety, circuit protection, and the proper operation of the device. The National Electrical Code (NEC) – NFPA 70 provides guidelines to ensure that electrical systems are safe, functional, and compliant with national standards. This article outlines the requirements and considerations for selecting the appropriate wire size for a 20A breaker and outlet according to NEC guidelines.

Correct Wire Size for 20-Amp Breaker and Outlet

Why is the Correct Wire Size Important?

Using the correct wire size for a breaker, outlet, and load points is essential for several reasons: safety, efficiency, code compliance, longevity, and durability.

Correct wire sizing prevents overheating, insulation damage, and fire hazards, minimizes voltage drop, and enhances the longevity of the electrical system. The suitable wire size also prevents premature insulation degradation, reduces the risk of frequent breaker trips and electrical faults, and ensures compliance with NEC 2020, IEC, and IEEE regulations to avoid potential liabilities and inspection issues. The right wire size ensures devices receive the proper voltage for efficient operation.

It is important to consider the breaker rating, load current, ampacity, type of wire and insulation, voltage drop, distance, and ambient temperature before selecting the right wire size for a breaker, outlet, and load applications.

If you are unsure about wiring installations, consult a licensed electrician to ensure compliance with local area codes.

What is the Suitable Wire Size for a 20A Breaker and Outlet?

Based on NEC Table 310.15(B)(16) (formerly Table 310.16), the standard wire size for a 20-ampere breaker is 12 AWG copper wire. A 12 gauge (AWG) copper wire can handle:

  • 20 amps at 60°C (140°F)
  • 25 amps at 75°C (167°F)
  • 30 amps at 90°C (194°F)

In the case of aluminum, the recommended wire size with a 20A breaker and outlet is 10 AWG. The ampacity of a #10 AWG aluminum is:

  • 25 amps at 60°C (140°F)
  • 30 amps at 75°C (167°F)
  • 35 amps at 90°C (194°F)

If you are going to wire and install a 20A breaker with a 20A outlet, then:

Good to know:

  • For a 20A circuit breaker and outlet, the correct wire size is #12 AWG copper or #10 AWG aluminum.
  • Use 12-2 with ground for 120V, 20-Amp breaker and load circuits.
  • Use 12-3 with ground for 240V, 20-Amp breaker and load circuits.
  • Use 12-4 with ground and neutral for 240V, 20-Amp breaker and load circuits.
  • Longer runs (when the distance is more than 50 ft (15.25 meters) require an upgrade and larger wire gauge size to compensate for voltage drop.

  • According to the NEC – 310-16, add 20% of additional ampacity for every 100 feet (30.50 meters) of distance (for example between main panel and subpanel) to counter the voltage drop.

How to Select the Right Wire Size for a 20A Breaker and Outlet?

The label printed on the device (i.e. water heater or air-condition in HVAC) shows the minimum circuit ampacity (MCA) and maximum overcurrent protect (MOCP). MCA is the amount of minimum load current the circuit will draw while the MOCP shows the recommended fuse or breaker rating with the desired appliance or device.

Suppose you have a 2-pole, 20A breaker installed in the main panel, and you want to wire it to a 20A outlet or load circuit. Follow these steps to find the correct wire size according to the NEC, which is based on the breaker, not the outlet or load circuit.

Example:

If the Load is Continuous

The 125% rule (also known as the continuous load rule) in the NEC states that the OCPD (Overcurrent Protection Device i.e. fuse or breaker) size should handle 125% of the continuous load. As a safety factor, only 80% of the continuous load should be connected to the rated breaker.

20A × 80% = 16A

This shows that only 16A of continuous load should be connected to the 20A breaker. The same applies to a 20A outlet.

As the load circuit amperes are 16A, to find the breaker size for this circuit:

16A × 125% = 20A

According to NEC Table 310.15(B)(16), the 12 AWG wire size can carry 20A at 60°C (140°F) and 25A at 75°C (167°F).

If the Load is Non-continuous

For non-continuous loads (e.g., lighting circuits), the conductor size should be no less than 100%. The same applies to overcurrent protection devices (OCPDs).

Hence, a 20A breaker can be used for a maximum of 20A circuits (e.g., outlets) while considering the ambient temperature rating [Refer to 110.14(C) and 310.15(B)(2)].

  • Good to Know: Always consider the voltage drop in long distance circuits and ambient temperature when selecting the wire size.

How Many Amps Can a 20A Breaker Handle Safely?

The maximum current-handling capacity of a 20-amp breaker is 20A. According to the 125% safety factor, only 80% of the branch circuit load should be connected to the circuit:

20A × 80% = 16A

While it can handle up to 20A of non-continuous load, only 16A max of continuous load circuit should be connected to a 20A breaker and outlet. i.e.:

  • Use a 20A breaker and outlet for a 16A continuous load circuit.
  • Use a 20A breaker and outlet for a 20A non-continuous load circuit.

The rating of the breaker and outlet, and the ampacity of the wire size, comply with the National Electrical Code (NEC) – Sections 210.19(A), 215.2, and 230.42(A) for continuous and non-continuous loads, and 110.14(C) for ambient temperature.

The above calculations are based on NEC Table 310.15(B)(16) and 240.4(A) through (G), illustrating that the 12 AWG wire size can carry 20A at 60°C (140°F) and 25A at 75°C (167°F).

Good to know: Use a 20A breaker and outlet for 16A continuous load circuits or maximum 20A non-continuous load circuits.

How Many Watts Can a 20-Amp Breaker and Outlet Hold?

120V Circuit

In a 120V circuit, a 1-P, 20-amp breaker holds a maximum of 2,400 watts:

20A × 120V = 2,400 watts

If we apply the safety factor of 80% of the load to a rated breaker and outlet:

20A × 80% = 16A

Hence, no more than 1,920 watts of load should be connected to a 20A breaker and outlet:

16A × 120V = 1,920 watts

As an example load, you may use 20A breaker in 120V circuit with 1.5kW to 1,700 Watts water heater element.

  • Good to know: A 1-pole, 20A breaker in 120V circuit can be connected to the associated outlets such as NEMA 2-20R, 5-20R, 10-20R or 14-20R etc.

240V Circuit

In a 240V single-phase AC circuit, a 20-amp breaker holds a maximum of 4,800 watts:

20A × 240V = 4,800 watts

Applying the safety factor of 80% of the load to a rated breaker and outlet:

20A × 80% = 16A

Based on the above calculation, no more than 3,840 watts of load having 16A of current should be connected to a 20A breaker and outlet:

16A × 240V = 3,840 watts

For example, you may use 20A breaker with 240V, 3kW, 3.5kW or 3.8kW water heater element.

Based on the above calculations, A 20A breaker and outlet can handle a maximum of 2,400W and safely 1,920W in a 120V circuit, while it can handle a maximum of 4,800W and safely 3,840W in a 240V circuit.

  • Good to know: A 2-pole, 20A breaker in 240V circuit can be wired for the rated outlets such as NEMA 2-20R, 6-20R, 10-20R, 14-20R etc.

How Many Outlets Can be Installed on a 20A Breaker?

A 20-amp circuit can support around 10 outlets, assuming a maximum 1.5 amp draw per outlet. However, the exact number depends on the electrical load, not the number of outlets.

The National Electrical Code (NEC) recommends limiting circuit loads to 80% of their maximum capacity for continuous use. This means a 20-amp circuit, which can handle 2,400 watts, should be limited to 1,920 watts or 16 amps:

20A × 80% = 16A

16A × 120V = 1,920 Watts … (in 120V circuits)

16A × 240V = 3,840 Watts … (in 240V circuits)

Dividing 16 amps by 1.5 amps per outlet gives an estimate of 10.67 outlets, which rounds down to 10.

However, this is a theoretical maximum and not recommended in practice to avoid overloading. For more details, refer to the NEC table – 210.21(B)(3) for receptacles rating for various size circuits which clarify the circuit rating and receptacle rating in amperes.

Can I Use a #10 AWG or 14 AWG Instead of #12 AWG Copper Wire on a 20-Amp Breaker?

#10 AWG Instead of #12 AWG:

According to the NEC, using #10 AWG instead of #12 AWG on a 20A breaker is permissible because #10 AWG wire can handle 30A at 60°C (140°F) and 35A at 75°C (167°F). While doing so, this approach might not be cost-effective, and the larger wire may not fit into the terminals of some 20-amp devices or fixtures.

#14 AWG Instead of #12 AWG:

Using #14 AWG instead of #12 AWG on a 20A breaker is against the code and not recommended. The #14 AWG wire can handle only 15A at 60°C (140°F). Using a lower ampacity wire size with a higher rated breaker may overheat the wire, leading to fire hazards and circuit damage.

What Happens If the Wrong Wire Size is Used with a Breaker?

If you use a smaller wire gauge than recommended (e.g., using 14 or 16 AWG with a 20A breaker, which is against the code), it might overheat, increase the voltage drop, and trip the breaker. This scenario may also lead to insulation failure, which can cause a serious fire and electric shock.

If you use a larger wire gauge than recommended (e.g., using 8 or 10 AWG with a 20A breaker), you will need larger conduits for the larger wires and may face difficulty in installation because thicker wires may not fit in the fixtures and outlets. It also increases the initial cost because larger gauge wires are more expensive.

What Happens if a 14 AWG Wire is Connected to a 20A Breaker?

Connecting a 14 AWG wire to a 20A breaker is unsafe. The 14 AWG wire is rated for 15A, not 20A. This can cause:

  • Overheating: 14 AWG wire may overheat under a 20A load.
  • Fire Hazard: Increased risk of fire due to overheating.
  • Code Violation: Non-compliance with NEC standards.

Using the correct wire size is essential for safety, efficiency, and code compliance. For a 20A breaker, use 12 AWG copper wire or 10 AWG aluminum wire to ensure your electrical system operates safely and reliably. If in doubt, consult a licensed electrician to ensure compliance with local codes and standards.

Suitable Types of Cables for a 20A Breaker and Outlet

The following types of wires and cables are suitable with 20A breaker and outlet.

In the case of copper wire:

  • NM-B (Non-Metallic Sheathed Cable), known as ROMEX
  • MC (Metal-Clad Cables)
  • THHN/THWN
  • UF-B

In the case of aluminum wire:

  • USE for underground service
  • SE for service entrance

Applications of a 20A Breaker and 20A Outlet

Common residential and commercial applications of 20A breakers and 20A outlets include:

  • Kitchen appliances
  • Bathrooms
  • Laundry rooms
  • Power tools
  • Workshops and garages
  • Home offices
  • Heating and cooling systems (HVAC)
  • Outdoor equipment
  • Dedicated circuits

Good to Know:

  • The ampere rating of a single receptacle installed on an individual branch circuit should not exceed that of the branch circuit.
  • The above calculations for breaker and wire sizes are only applicable to purely resistive load circuits, such as lighting.
  • For inductive loads, such as air conditioner compressors and fan motors in HVAC systems, refer to NEC Article 440, particularly sections 440.22 and 440.32, which were added in 2017. If not sure, consult an HVACR contractor, instructor, and electrician.
  • A 20A branch circuit needs #12 AWG wire size for copper – NEC Table 210.24.(1).
  • A 20A outlet can be used for a 16A (continuous) load and a maximum 20A (non-continuous) load (210.19(A) and 210.20(A)).
  • A 120V/240V, 20A outlet can only be installed on 20A breaker. It is against the code to use a 20A outlet to draw 20A on a 15A breaker.
  • It is also against the code to use smaller gauge wire sizes (e.g., using 14 AWG) instead of the recommended wire size, which is #12 AWG with a 20A breaker and outlet.
  • A 20A breaker and outlet can support a 16A continuous load and a 20A non-continuous load, per NEC sections 210.19(A), 215.2, and 230.42(A).
  • According to NEC 210.21(B)(3), it is permissible to use a 15A outlet on a 20A circuit if there are multiple receptacles on the circuit.
  • If you install a 15A outlet on a 20A circuit, it should only be used for a maximum of a 15A load. Drawing more than 15A from a 15A outlet will overheat the circuit, potentially causing serious injury and fire hazards.
  • For optimal safety, consult a licensed electrician to verify the appropriate wire size for your specific installation, ensuring compliance with NEC standards.

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