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How to Size a Breaker and Wires in AWG with EGC for Load?

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Proper Sizing of Breakers and Wires in AWG with Equipment Grounding Conductor (EGC) for Branch Circuits – Based on Load Current, Wattage, and Supply Voltage in Single-Phase and Three-Phase Systems

Sizing breakers and selecting the correct wire size in AWG is not rocket science. If you are unfamiliar with electrical codes, or simply tired of reading lengthy articles and doing complex calculations, you are in the right place. Even a beginner can figure it out without the help of an electrician or electrical engineer.

Bored with the introduction? No problem! we’ve got you covered. Below, you’ll find a comprehensive table that clearly shows the appropriate breaker size and wire gauge based on load current, wattage, and supply voltage for both single-phase and three-phase branch circuits.

Alright, that’s enough – let’s get started to find the branch circuit conductors with EGC and breaker size for overcurrent protection.

How to Size Breaker and Wire Size with EGC in AWG?

120V/240V – Single-Phase Circuit

Example:

What size of conductor and breaker should I use for a 1,920 W water heater operating at 120V single-phase?

Solution-1:

First, calculate the load current using Ohm’s Law:

I = P ÷ V

I = 1,920 W ÷ 120V

I = 16 – Amp

Now, refer to the following table (based on NEC Table 310.16) to determine the proper wire size and breaker rating. For a 16A load at 120V single-phase, the correct choice is a 20A single pole breaker with #12 AWG copper conductors, rated for 60°C (140°F) ambient temperature. Similarly the wire size for equipment ground conductor (EGC) is 12 AWG (based on NEC Table 250.122). This combination is sufficient to handle and protect the 1,920 W load.

But why use a 20A breaker and #12 AWG wire instead of a 15–16A breaker and #14 AWG wire?

According to NEC 210.19(A)(1), branch circuit conductors must be rated at 125% of the continuous load (a load running for 3 hours or more). This rule of thumb is also known as 125% rule.

This way,

= 16A × 1.25 = 20 – Amp

Therefore, the correct selection is a 20A breaker with #12 AWG wire.

For non-continuous loads (operating less than 3 hours, e.g., hair dryers), the breaker and conductor may be rated equal to the load current instead of applying the 125% rule.

Solution-2:

Alternatively, refer to the table. As per the table data, a 1,920-watt load requires a 20-ampere overcurrent device and #12 AWG copper conductors as well as #12 AWG copper for equipment grounding conductor (EGC).

480V – Three-Phase Circuit

Example:

What is the correct wire size and breaker rating for a 9,975 W induction cooktop operating at 240V, three-phase supply?

Solution 1:

The method is same as above i.e. use the three-phase power formula to calculate the load current in amps. Since this is a resistive load, power factor (P.F.) = 1.

P = √3 × V × I

I = P / (√3 × V)

I = 9,975W / (1.732 × 480V)

I ≈ 24 – Amp

Apply the NEC 125% rule for continuous loads.

24A × 125% = 30A.

Therefore, a 30A double pole breaker is required. Similarly, #10 AWG copper conductors (at 60°C (140°F) ambient temp.) are suitable for a 9,975 W load operating on a 30A, 240V three-phase supply. In addition, the same size is required for equipment grounding conductor (EGC) i.e. #10 AWG copper (NEC Table 250.122).

Good to Know: For non-continuous loads (operating less than 3 hours), you may size the breaker directly to the load current. In other words, a 25A breaker with #10 AWG wire would be acceptable.

Solution 2:

Refer to the table and select based on either load wattage or current. For example, a 30A breaker with #10 AWG copper conductors and equipment grounding conductors can safely be used for a 24A (≈ 9,975 W) continuous load operating at 240V three-phase.

Caution:

If you are still unable to manage the wiring installation, consult a licensed electrician to ensure it is done properly and in compliance with code requirements. The author(s) of this guide assume no liability for any damage to persons or equipment.

Table for Breaker & Wire Size with EGC

Sizing Breaker, Wire, and Equipment Grounding Conductor (EGC) for Single-Phase and Three-Phase Loads (Based on Load Current and Wattage)

NOTE:

See the notes below the table. They apply to continuous load points. For non-continuous load points (such as lighting circuits), the 125% (or 80%) rule does not apply. Therefore, you can use the full circuit rating – for example, a 15A breaker for a 15A circuit, and so on.
The following table should not be used for motor circuits. Motor circuits, controllers, and wire sizing requirements differ from those of lighting circuits. A separate and detailed 14-part series on motor circuits is published on this site

Breaker Size & Wire Size with EGC for Branch Circuit Current, Load Wattage, & Supply Voltage – 1-Phase & 3-Phase Circuits
Load Current in Amp	Breaker Size (A)	Wire Size (AWG)	EGC Size (AWG)	Single – Phase		Three – Phase
				120V	240V	208V	240V	480V
				Max Watts		≈ Max Watts
10	15	14	14	1,200	2,400	3,605	4,155	8,315
12	15	14	14	1,440	2,880	4,325	4,990	9,975
15	20	12	12	1,800	3,600	5,405	6,235	12,470
16	20	12	12	1,920	3,840	5,765	6,650	13,300
20	25	10	10	2,400	4,800	7,205	8,310	16,625
24	30	10	10	2,880	5,760	8,645	9,975	19,950
30	40	8	10	3,600	7,200	10,810	12,470	24,940
35	45	6	10	4,200	8,400	12,610	14,550	29,100
40	50	6	10	4,800	9,600	14,410	16,630	33,255
45	60	4	10	5,400	10,800	16,210	18,705	37,410
50	70	4	8	6,000	12,000	18,010	20,785	41,565
60	80	3	8	7,200	14,400	21,615	24,940	49,880
80	100	1	8	9,600	19,200	28,820	33,255	66,505
90	125	1/0	6	10,800	21,600	32,420	37,410	74,820
100	125	1/0	6	12,000	24,000	36,025	41,565	83,135
Table is Based on NEC Table 310.16 for Wire & Breaker Size. The Table Shows the Wire & Breaker Size for Continuous Load (Lasts More than 3-Hrs) Mentioned in NEC – 210.19. For This purpose, 1.25 Safety Factor is used with Amps for Breaker Size & Wire Size. For Non- Continuous Load (Runs Less than 3-Hrs), You May Use the Exact Current in Amps Rating for Wire & Breaker Size Mentioned in Columns (A). The Table Shows the Data for Pure Resistive Load e.g. Lighting Circuits, Water Heater Elements, Stoves etc. No Power Factor for Inductive and Capacitive Load involved. Sizing Equipment Grounding Conductor (EGC) is Based on NEC Table 250.122. Use Proper Ambient Temperature Factor in 310.15(B)(1)(1) & Other Applicable Correction Factors.

The tables below are available in image format for easy reference and download.

Click image or open in a new tab to enlarge

Related Resources, Tutorials & Wire Sizing Guides:

How to Size a Breaker and Wires in AWG with EGC for Load?

Proper Sizing of Breakers and Wires in AWG with Equipment Grounding Conductor (EGC) for Branch Circuits – Based on Load Current, Wattage, and Supply Voltage in Single-Phase and Three-Phase Systems