What is the Right Wire Size for 45A Breaker and Load?

Electrical Technology

How to Determine the Correct Wire Size for a 45A Breaker and Load Circuits Based on NEC?

45-Amp breakers are less common than the usual 20A, 30A, or 40A breakers. They are typically used for heavy-duty equipment such as air conditioner condensers, electric ranges, heaters, and other applications like HVAC systems. In this technical article, we will demonstrate how to determine the correct wire size for a 45A breaker in AWG for personal and circuit protection in compliance with the National Electrical Code (NEC) NFPA 70.

According to NEC tables and charts, the correct wire size for a 45-amp circuit is #6 AWG copper or #4 AWG aluminum. Keep in mind that the correct wire size depends on multiple factors such as distance, voltage drop, ambient temperature, type of cable and wire, type of insulation, etc.

Related Post: What is the Correct Wire Size for a 40A Breaker and Load?

Table of Contents

Toggle

What is the Suitable Wire Size for a 45A Breaker and Load?

Based on NEC Table 310.15(B)(16) (formerly Table 310.16), the standard wire size for a 45-ampere breaker is #6 AWG copper wire.

On the other hand, you may opt out to use larger #4 AWG aluminum wire size due to aluminum’s lower conductivity and high resistance compared to copper.

Both #6 AWG copper and #4 AWG aluminum wires can handle:

55A at 60°C (140°F)
65A of current at 75°C (167°
75A at 90°C (194°F)

Due to the heavy duty circuit, it is a good practice to use #6 gauge solid copper wire instead of #4 gauge aluminum or stranded wire with 45A breakers, outlets, and load circuits for the safety, better conductivity, and overall efficiency of the circuit. Solid wire offers advantages over stranded wire, which is why U.S. homes typically use solid wire rather than stranded wire.

Good to Know:

For a 45A circuit breaker, the correct wire size is #6 AWG for copper and #4 AWG for aluminum.
Use 14-2 with ground for 120V, 45-Amp breaker and load.
Use 14-3 with ground for 240V, 45-Amp breaker and load.
Use 14-4 with neutral and ground for 240V, 45-Amp breaker and load.
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.

Related Post: What is the Right Wire Size for a 30A Breaker and Outlet?

How to Select the Right Wire Size for a 45A Breaker and Load?

The following example shows the correct wire selection for 45A breaker and associated continuous and non-continuous load circuits:

Example:

Find the suitable wire size for a 45-Amp (either 1-pole or 2-pole) breaker and load circuits for both continuous and non-continuous load circuits according to NEC guidelines.

Continuous Load Circuit

The NEC’s 125% rule states that the maximum overcurrent protection device (MOCP) should handle 125% of the continuous load. As a safety factor, no more than 80% of the continuous load should be connected to the Overcurrent Protection Device (OCPD).

45A × 80% = 36A

Based on this rule, the amperes of the load circuit should not exceed the maximum limit of 36A. In other words, you may only wire a 36-Amp of continuous load (which lasts for 3-4 hours simultaneously) circuit to a 45-Amp breaker.

On the other hand, where the minimum circuit ampacity (MCA) i.e. load circuit’s amperes are 36A, you may find the correct breaker size for this circuit:

36A × 125% = 45A

According to NEC Table 310.15(B)(16), the #6 AWG wire size can carry 55A at 60°C (140°F) and 65A at 75°C (167°F).

Non-continuous Load Circuit

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

A 45A breaker can handle a maximum of 45A non-continuous load circuits, such as outlets and lighting circuits, while considering distance and ambient temperature rating (Refer to 110.14(C) and 310.15(B)(2)).

Related Post: What is the Correct Wire Size for 25A Breaker and Load?

How Many Amps Can a 45A Breaker Handle Safely?

A 45-amp breaker can safely handle a maximum of 45 amps of current. The NEC specifies that breakers should not exceed 80% of their rated capacity for continuous loads (lasting three hours or more). Therefore, a 45A breaker is suitable for a maximum of 36A continuous load circuits.

45A × 80% = 36A

For short, non-continuous loads, the breaker can handle up to 36 amps safely.

Use a 45A breaker for a 36A continuous load circuit.
Use a 45A breaker for a 45A non-continuous load circuit.

These ratings comply with 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 8 AWG copper wire size can carry 40A at 60°C (140°F) and 50A at 75°C (167°F) which is the suitable size to use with a 45-Amp breaker.

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

How Many Watts Can a 45A Breaker Hold?

The power capacity of a 45-amp breaker can be calculated using the following formula:

$Watts = Volts \times Amps$

120V Circuit

In a standard 1P, 120V circuit, the max power a 45A breaker can hold:

45 A × 120 V = 5,400 W

Applying the safety factor (80% Load):

45 A × 80% = 36 A

Hence, no more than 4,320 watts of load should be connected to a 45A breaker:

It means, you may use 45A breaker with a 120V, 4kW to 4.2kW electric water heater elements.

240V Circuit

A 2-P, 45A breaker in 240V circuit can hold the maximum power:

45 A × 240 V = 10,800 W

Applying the safety factor of 80% for continues load:

45 A × 80% = 36 A

No more than 8,640 watts of load should be connected to a 2-pole, 240V, 45A breaker:

36A × 240V = 8,640 watts

For example, you may use a 45A breaker with a 240V, 8kW to 8.5kW electric ranges or water heater elements.

These calculations assume that the breaker is not continuously loaded to 100% of its capacity. For continuous loads, the safe wattage is 80% of these values:

120V Circuit (Continuous Load): 4,320 W
240V Circuit (Continuous Load): 8,640 W

Related Post: What is the Right Wire Size for 15A Breaker and Outlet?

How Many Outlets Can be Put on a 45A Breaker?

45A breaker are generally used with a dedicated circuit and outlet for high wattage appliances such as electric ranges, water heaters. It means, 45A breakers are not supposed to wire with 15A and 20A outlets.

As a general assumption and calculation based on the ampacity, 36A of maximum safe current of a load circuit may be connected with a 45A breaker. If each outlet is assumed to draw 1.5A of current:

36 A ÷ 1.5 A ≈ 24 outlets

Keep in mind that 45A breakers are hardwires as dedicated circuits without receptacles and outlets. In other words, it is used for one device per outlet. For more details, Refer to NEC Table 210.21(B)(3) for receptacle ratings for various circuit sizes.

Suitable Types of Cables for a 45-Amp Breaker

For a 45-amp breaker, selecting the correct cable type is essential for safety and compliance with electrical standards. The suitable types of cables are as follows:

1. Copper Conductors

Size: 6 AWG (American Wire Gauge)
Insulation Type: The insulation should be rated for the environment, such as THHN (Thermoplastic High Heat-resistant Nylon-coated) for dry locations or THWN-2 (Thermoplastic Heat and Water-resistant Nylon-coated) for wet locations.
Advantages: Copper conductors offer lower resistance, better conductivity, and superior mechanical strength.

2. Aluminum Conductors

Size: 4 AWG
Insulation Type: Similar to copper, THHN or THWN-2 insulation types are typically used, depending on the environment.
Additional Considerations: Aluminum conductors should be installed with anti-oxidation compound on connections to prevent corrosion. Aluminum is less conductive than copper, so a larger gauge is needed to carry the same current.

3. Copper-Clad Aluminum Conductors

Size: 6 AWG
Insulation Type: Again, THHN or THWN-2 insulation is commonly used.
Advantages: Copper-clad aluminum combines the lightness and cost-effectiveness of aluminum with the superior conductivity of copper. However, it is less common than pure copper or aluminum.

Applications of a 45-Amp Breaker:

Electric Water Heaters: Some large-capacity water heaters may require a 45-amp breaker, especially in commercial or industrial settings.
Air Conditioning Units: Certain central air conditioning systems, especially those with higher capacities, might require a 45-amp breaker.
Electric Furnaces: Some larger electric furnaces or heat pumps may be wired to a 45-amp breaker, particularly in residential settings with higher heating demands.
EV Charging Stations: High-capacity electric vehicle (EV) charging stations, particularly those designed for faster charging, may require a 45-amp breaker.

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 apply only to purely resistive load circuits, such as lighting.
For inductive loads (motors and HVAC), refer to NEC Article 440, particularly sections 440.22 and 440.32. If not sure, consult an HVACR contractor, instructor, and electrician.
A 45A branch circuit needs #6 AWG wire size for copper – NEC Table 210.24.(1).
A 45A outlet can be used for a 36A continuous load and a maximum 45A non-continuous load (210.19(A)).
It is against code to use a 50A outlet to draw 50A on a 45A breaker.
It is against code to use smaller gauge wire sizes (e.g., using 10, 12 AWG) instead of 6 AWG wire with a 45A breaker.
According to NEC 210.21(B)(3), it is permissible to use a 40A outlet on a 45A circuit if there are multiple receptacles on the circuit and only one operates at a time.
Important Note: If you install a 45A outlet on a 45A circuit, it should only be used as dedicated circuit for single appliance or outlet for a maximum of a 36A load. Drawing more than 36A simultaneously from a 45A breaker will overheat the circuit, potentially causing serious injury and fire hazards.