How Many Outlets on a 15-Amp or 20-Amp Circuit? NEC Rules

The NEC’s Approach to Receptacle Loads

It’s a common misconception in the electrical trade that there’s a hard limit—such as 10 or 13 outlets—on a circuit. This “rule of thumb” has no basis in the NEC. In fact, for dwelling units (residential settings), the NEC does not limit the number of general-use receptacles on a circuit; their load is included in the general lighting load calculation based on square footage per NEC 220.14(J). The specific outlet-counting method using the 180 VA value applies to non-dwelling occupancies to ensure the circuit can handle the anticipated load without tripping the overcurrent protection device (OCPD) or creating a fire hazard.

NEC Article 210 provides the foundational requirements for branch circuits. It distinguishes between a receptacle outlet vs. lighting outlet and circuits for specific uses, such as a dedicated small appliance branch circuit in a kitchen. For general-use receptacles, the code shifts from counting devices to calculating potential load, which offers greater design flexibility while maintaining safety.

Calculating Receptacle Loads in Non-Dwelling Units: The 180 VA Rule

The core of this topic for non-dwelling units lies in understanding and applying NEC 220.14(I). This section states that for outlets, each single or multiple receptacle on one yoke is to be calculated at a minimum of 180 volt-amperes (VA). This allows for a standardized noncontinuous load calculation, even when the exact devices to be plugged in are unknown.

Let’s perform a step-by-step wire size computation and load calculation to determine the theoretical maximum number of receptacles.

1. Determine Total Circuit Capacity (VA): First, find the total volt-amperes the circuit can supply. VA is calculated by multiplying the circuit voltage by the amperage. For a standard 120V circuit:
   • 15-Amp Circuit: 120V x 15A = 1,800 VA
   • 20-Amp Circuit: 120V x 20A = 2,400 VA
2. Apply the Continuous Load 80% Rule (as a Best Practice): Per NEC 210.19(A)(1) and 210.20(A), circuits supplying continuous loads (those operating for 3 hours or more) must be sized to 125% of the load, which is equivalent to loading the circuit to only 80% of its rating. While general-purpose receptacle loads are typically considered noncontinuous, applying this 80% factor is a conservative best practice to build in a safety margin.
   • 15-Amp Circuit (Conservative): 1,800 VA x 80% = 1,440 VA
   • 20-Amp Circuit (Conservative): 2,400 VA x 80% = 1,920 VA
3. Divide by 180 VA per Yoke: Now, divide the available capacity by the 180 VA per receptacle yoke value to find the maximum number of outlets.
   • 15-Amp Circuit: 1,440 VA (Conservative) / 180 VA = 8 Receptacles. (For noncontinuous loads at full capacity, 1,800 VA / 180 VA = 10 Receptacles.)
   • 20-Amp Circuit: 1,920 VA (Conservative) / 180 VA = 10.66, which rounds down to 10 Receptacles. (For noncontinuous loads at full capacity, 2,400 VA / 180 VA = 13.33, allowing 13 Receptacles.)

Based on the conservative, derated calculation for non-dwelling units, a 15-amp circuit can support 8 receptacle yokes, and a 20-amp circuit can support 10. While this specific calculation is not a code requirement for counting outlets in homes, it is a valuable guideline for all electricians to avoid overloading circuits and ensure robust design.

Practical Considerations Beyond the Code Minimum

While the 180 VA calculation provides a code-compliant answer for commercial jobs, practical application requires more foresight. For instance, if you know a circuit will power a home office, you must consider how many computer on one breaker is feasible. A few powerful workstations could easily exceed the load, even with only a few outlets. This is where professional judgment is key. In commercial applications, a demand factor calculation may be permitted for large numbers of receptacles, but this requires careful application of NEC 220.44.

It is also important to consider the specific requirements for different areas. For example, understanding how many 15-amp and 20-amp circuits are needed in a garage involves rules beyond the general-purpose calculation. For continuous runs of outlets, such as in a workshop, a multi-outlet assembly has its own set of calculation rules per NEC 220.14(H). To master these nuances and stay ahead, it’s essential to stay current with your training. Understand the nuances of branch circuit design with our NEC courses.

Wire Sizing and Ampacity: The Foundation of a Safe Circuit

The entire discussion of circuit loading is built on the foundation of proper wire sizing. The circuit ampacity must never exceed the ampacity of the wire. For a 20-amp circuit, a minimum of 12 AWG for 20-amp circuit (copper) is required, while a 15-amp circuit requires 14 awg wire. Using undersized wire is a major fire hazard. Knowing how to know what gauge wire to use is a fundamental skill for any electrician, and it starts with consulting an ampacity chart.

Understanding the Wire Ampacity Chart

The definitive source for this information is the nec ampacity chart, primarily NEC Table 310.16. This ampacity table lists the allowable ampacity for insulated conductors based on cable gauge awg, insulation type (like THHN), and ambient temperature. Electricians frequently reference this nec wire ampacity chart, also known as a wire amperage chart, wire amp chart, or ampacity of cable table. Whether you need a full electrical wire size chart or a quick reference from the nec amp chart, understanding these tables is non-negotiable for safe installations. You can also find a specialized nec wire size chart, nec wiring size chart, or nec code wire size chart to assist with quick lookups.

Sizing Conductors for Various Loads

The principles of matching wire to OCPD extend to all circuits. For a 30 amp wire size (e.g., for a clothes dryer with a specific dryer wattage), 10 AWG copper is standard. For a 40 amp wire size, you typically need 8 AWG. A common query is what size wire for 50 amp; the answer is usually 6 AWG copper. This also answers questions like “what size wire for 50 amps?” or “what size wire for 50 amp breaker?”. The 50 amp wire size (or 50 amp wire/50 amps wire size) is critical for ranges or EV chargers. For a 60 amp wire size, you’d move up to 4 AWG copper. To determine the correct size of wire for 60 amp or a 60 amp breaker wire size, always consult the ampacity chart nec. The wire size for 60 amp must be respected.

For larger services and feeders, the requirements grow. Questions like what size wire for 100 amp service or the proper 100 amp sub panel wire size are common. For a 100-amp single-phase dwelling service, NEC 2023 Table 310.12(A) permits the use of 4 AWG copper or 2 AWG aluminum. The correct 100 amp wire size is crucial for safety. For even larger installations, a 200 amp service wire size might be 2/0 copper or 4/0 aluminum wire, while a 400 amp wire size would require much larger parallel conductors. An electrical wire size table or a digital size electrical wire calculator can simplify this wire size computation, but always verify against the nec ampacity table, accounting for voltage drop with a wire length calculator for long runs. You may also need to consider sizing for a mobile home feeder wire 100 amp service, which has its own specifications.

Specific conductor types have unique ratings. The 8 gauge wire amp rating depends on the insulation and termination ratings; the amp capacity of 8 gauge wire is often listed as 40A or 50A. The 8 awg ampacity, specifically 8 thhn ampacity, is 55A in the 90°C column, but is limited by terminal ratings. The amp rating for 8 gauge wire (or 8 awg wire amps / 8awg wire ampacity) must be carefully determined. Similarly, 4 awg wire ampacity is 95A for THHN, 2 awg ampacity is 130A, and 3/0 copper wire ampacity is 225A. For aluminum, the 4/0 aluminum wire ampacity is 205A, while #2 aluminum ampacity is 90A. You might see other aluminum sizes like 2/0 aluminum wire, 1/0 al wire, or 4-0 aluminum electrical wire. The wire ampacity for smaller conductors like 14 gauge wire amps is 15A for most applications, while 16 awg ampacity is generally 10A, which is relevant in the context of 10-amp branch circuits permitted in the 2023 NEC. Lastly, don’t forget the grounding conductor, which is sized using a ground wire size chart like the nec ground wire size chart (Table 250.122), also known as an equipment grounding conductor chart or ground wire sizing chart.

Primary Sources

• NFPA 70, National Electrical Code (NEC), 2023 Edition

Frequently Asked Questions (FAQ)

How many receptacles on a 20 amp circuit are allowed by the NEC?

The NEC does not set a maximum number for dwelling units. For non-dwelling (e.g., commercial) applications, you must perform a branch circuit load calculation using the 180 VA per receptacle yoke rule from NEC 220.14(I). Assuming the load is noncontinuous, a 20-amp circuit can support 13 receptacles (2,400 VA / 180 VA). Using a conservative continuous load 80% rule as a best practice, the circuit would support 10 receptacles.

What’s the difference in calculation for how many outlets on a 15 amp circuit vs. a 20-amp?

The calculation method for non-dwelling units is the same, but the capacity differs. A 15A circuit provides 1,800 VA, allowing for 10 receptacles (1800/180). A 20A circuit provides 2,400 VA, allowing for 13 receptacles (2400/180). Applying a conservative 80% derating for safety reduces these numbers to 8 and 10 receptacles, respectively. In dwelling units, there is no specific receptacle count limit for general-purpose circuits.

Can I put a 20 amp outlet on a 15 amp circuit?

No. Placing a 20 amp outlet on a 15 amp circuit is a code violation. The receptacle type (e.g., a NEMA 5-20R receptacle) must match the circuit’s rating to prevent users from plugging in a 20-amp appliance that would overload the 15-amp OCPD and 14 awg wire. However, you can install 15-amp receptacles on a 20-amp circuit if there is more than one receptacle on the circuit.

How does a branch circuit load calculation change for dedicated circuits?

For dedicated circuits serving a known load, you use the actual nameplate rating of the appliance instead of the 180 VA estimate. The continuous load 80% rule still applies if the appliance is expected to run for 3 hours or more. This provides a more accurate noncontinuous load calculation or continuous load calculation for specific equipment.

Where can I find an official nec wire ampacity chart?

The official nec wire ampacity chart is found in the NFPA 70, National Electrical Code, book. The primary table is Table 310.16, “Ampacities of Insulated Conductors.” Referencing the current edition of the NEC is the only way to ensure compliance and access the correct nec wire amperage chart.