Receptacle Rating & Branch-Circuit Load Calculator

Which receptacle the circuit allows (210.21(B))

The receptacle rules split on one question: is the receptacle the only one on its circuit, or does the circuit feed two or more? A single receptacle on an individual branch circuit is governed by 210.21(B)(1) and must be rated not less than the circuit - a lone receptacle on a 20 A circuit is a 20 A device, not a 15 A one. The moment the circuit supplies two or more receptacles, Table 210.21(B)(3) takes over and the familiar allowances apply: 15 A only on a 15 A circuit, 15 or 20 A on a 20 A circuit, 30 A on a 30 A circuit, 40 or 50 A on a 40 A circuit, and 50 A on a 50 A circuit.

That is why a duplex outlet stamped 15 A is perfectly legal on a 20 A kitchen or general-purpose circuit: the circuit has two or more receptacles, so Table 210.21(B)(3) governs, and 15 A receptacles are manufactured and listed with that use in mind.

How much load a receptacle may carry (210.21(B)(2))

Table 210.21(B)(2) caps the cord-and-plug-connected load on any one receptacle on a circuit supplying two or more receptacles: 12 A on a 15 A receptacle, 16 A on a 20 A receptacle, and 24 A on a 30 A receptacle. Each cap is exactly 80% of the receptacle rating - the same 80% idea that runs through the branch-circuit load rules. The table has no 40 or 50 A row, because those circuits are for individual equipment and cooking appliances rather than general receptacle use.

Permissible loads on the circuit (210.23)

Section 210.23 governs what a branch circuit as a whole may supply. On 15 and 20 A circuits, 210.23(A)(1) limits a single cord-and-plug-connected utilization equipment that is not fastened in place - a shop vacuum, a portable heater - to 80% of the circuit rating (12 A or 16 A). And 210.23(A)(2) adds the rule this tool makes explicit: where the same circuit also feeds luminaires or receptacles, equipment fastened in place (other than luminaires) may not exceed 50% of the circuit - 7.5 A on a 15 A circuit, 10 A on a 20 A circuit. A 30 A circuit carries the 80% cord-and-plug limit of 210.23(B) (24 A); 40 and 50 A circuits fall under 210.23(C) for cooking and fixed equipment, with no general 80%/50% receptacle rule.

2020 vs 2023: the (B)(3) wording change

This calculator defaults to the 2020 NEC, where Table 210.21(B)(3) says the receptacle rating "shall conform to" the listed values - so on a 15 A multi-receptacle circuit the receptacle must be 15 A, and a 20 A receptacle is not permitted. The 2023 NEC changed the wording to "shall not be less than," which lets you install a larger receptacle (for example a 20 A receptacle on a 15 A circuit). The tool flags that relaxation in its notes but does not apply it, so its answers match a 2020-adopted jurisdiction. Always confirm the edition your jurisdiction has adopted.

Worked examples

• 20 A general-purpose circuit, several receptacles. Table 210.21(B)(3) permits 15 or 20 A receptacles. A 15 A receptacle's cord-and-plug load is capped at 12 A and a 20 A receptacle at 16 A (Table 210.21(B)(2)).
• 20 A dedicated circuit, one receptacle. Now 210.21(B)(1) applies: the single receptacle must be rated not less than 20 A, so a 15 A receptacle is not permitted here.
• 30 A circuit, multiple receptacles. Only 30 A receptacles are listed (Table 210.21(B)(3)), with a 24 A maximum cord-and-plug load (Table 210.21(B)(2)) and a 24 A cord-and-plug equipment limit under 210.23(B).
• 15 A circuit feeding lights and a fixed disposal. The disposal is fastened in place, and the circuit also feeds lighting, so 210.23(A)(2) limits the disposal to 50% of 15 A = 7.5 A.

Frequently asked questions

What receptacle can I use on a 20 amp circuit?

On a 20 A circuit with two or more receptacles, Table 210.21(B)(3) permits 15 or 20 A receptacles, which is why 15 A duplex receptacles are common on 20 A circuits. A single receptacle on an individual 20 A circuit must be a 20 A device (210.21(B)(1)).

What is the maximum load on a receptacle?

Per Table 210.21(B)(2), the cord-and-plug load on one receptacle on a circuit with two or more receptacles is limited to 12 A (15 A receptacle), 16 A (20 A receptacle), or 24 A (30 A receptacle) - each 80% of the receptacle rating.

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

Yes, when the circuit supplies two or more receptacles. The 15 A receptacle is limited to a 12 A cord-and-plug load, and the 20 A circuit still protects the wiring. The exception is a single receptacle on its own individual circuit, which must match the circuit rating.

Does this size the wire or breaker?

No. This tool takes the branch-circuit rating as an input and answers the receptacle and permissible-load questions only. To size the conductor and overcurrent device from a load, use the Breaker Size and Wire Size calculators, cross-linked below.

Which NEC edition is this?

NEC 2020, the site default. The only edition-sensitive point is the (B)(3) "shall conform to" wording, which the 2023 NEC relaxed to "shall not be less than." The tool uses the 2020 reading and notes the 2023 change.

Related calculators

• Breaker Size Calculator: standard NEC 240.6(A) breaker for a load, with the 125% continuous rule.
• Wire Size Calculator: conductor ampacity and overcurrent protection for a branch circuit.
• Commercial Receptacle Load Calculator: the whole-occupancy receptacle demand with the NEC Table 220.44 factors.
• GFCI Breaker Sizing Calculator: whether NEC 210.8 requires GFCI protection for a location, then the device size.