Can You Use 15A Breaker on 20A Circuit and Vice Versa?

Electrical Technology

Is It Permissible to Use a 15-Amp Breaker on a 20A-Amp Circuit, or a 20-Amp Breaker on a 15A-Amp Circuit?

We often receive multiple queries regarding basic electrical wiring installations and DIY tasks at home. Today, we received a question (which can be confusing for a layperson) asking whether a 20-Amp breaker can be used on a 15-Amp circuit, and vice versa. Let’s now discuss this issue and the possible consequences of such setups in these specific cases.

While it is technically possible to use a 15-amp breaker on a 20-amp circuit or a 20-amp breaker on a 15-amp circuit, it is not recommended due to safety concerns and non-compliance with electrical codes. The second case (20A breaker on 15A circuit) is more dangerous which can cause serious damage and electrical fire hazards. Let’s see how?

Related Post: Can I Use a 240V Breaker on a 120V Circuit and Vice Versa?

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Using 15-Amp Breaker on a 20-Amp Circuit

Possible, but not ideal! A 15-amp breaker can be used on a 20-amp circuit with 12-gauge wire rated for 20 amps. The breaker protects the branch circuit wires, and since 12 AWG can handle 20A, a 15A breaker won’t overload it. In case of overcurrent, the breaker will trip at 15 amps, which is below the wire’s capacity. This setup is safe but limits the circuit’s capacity, as the breaker will trip before the circuit can handle its full 20-amp potential.

Why It is Not OK – Possible Issues and Risks:

The circuit is designed for 20A loads, so a 15A breaker may trip unnecessarily under normal usage (e.g., multiple devices drawing 16A).
You won’t be able to use the full capacity of the circuit (e.g., appliances or devices requiring more than 15 amps will cause the breaker to prematurely trip).
The National Electrical Code (NEC), requires the breaker to match the circuit’s design capacity. NEC 210.21(B) requires receptacles on a 20A circuit to be 20A-rated (or a mix of 15A/20A if multiple outlets exist (210.21(B)(3) or cord and plug connected load to receptacles as per 210.21(B)(2)). If you downgrade to a 15A breaker, you may violate code if the receptacles are 20A-only.
It could cause confusion for future electricians working on the system.

Hence, it is recommended to use the right size breaker to based on wire size in accordance with Table 310.16 to protect the branch circuit conductors and prevent nuisance and unwanted tripping of the breaker.

Related Post: Can You use a 15A Outlet on a 20A Circuit and Vice Versa?

Good to know:

#12 AWG wire is used for 20-Amp circuit and breakers.
A 20-Amp circuit can be used for 16-Amp continuous load (1,920 Watts at 120V or 3,840 Watts at 240V) and 20-Amp non-continuous load (2,400 Watts at 120V or 4,800 Watts at 240V). NEC – 210.19(A) and 210.20(A).

Using 20-Amp Breaker on a 15-Amp Circuit

While technically possible, but highly dangerous and violates code (NEC 240.4(D)). Hence, Not Allowed!

14 AWG wire is only rated for 15A. A 20A breaker won’t trip before the wire overheats, creating a fire risk.

If you use a 20-amp breaker on a circuit wired for 15 amps (typically 14 AWG wire), the breaker may allow more current than the wire can safely handle. This can cause the wires to overheat, potentially leading to electrical fires.

Installing a 15-amp breaker on a circuit designed for 20 amps (usually using 12 AWG wire) may cause frequent tripping even under normal load, as the breaker is not rated to handle the expected current.

Why it is Not Allowed?

A 20-amp breaker should not be used on a 15-amp circuit (with 14-gauge wire rated for 15 amps). The breaker will allow up to 20 amps of current to flow, which exceeds the wire’s capacity. In addition, it doesn’t makes sense as the 20-Amp breaker won’t be able to protect the 15-Amp branch circuit conductors. Consequently, this practice can potentially cause overheating, fire hazards, or damage to connected devices.

Receptacles on a 15A circuit must be 15A-rated (NEC 210.21(B)(1)). The NEC requires the breaker to match or be less than the ampacity of the circuit’s wiring to prevent overheating. Using a 20-amp breaker on 14-gauge wire violates this rule. Therefore, never use a 20A breaker on 15-Amp, 14 AWG wiring circuits.

Good to know:

#14 AWG wire is used for 15-Amp circuit and breakers.
A 15-Amp circuit can be used for 12-Amp continuous load which runs continuously for 3 hours (1,440 Watts at 120V and 2,880 Watts at 240V) and 15-Amp non-continuous load (1,800 Watts at 120V and 3,600 Watts at 240V). NEC – 210.19(A) and 210.20(A).

To be on the safe side, use the correct breaker size for the wire and load wattage and ampere rating for general-purpose circuits. This way, use a 15-amp breaker for a 15-amp circuit (14-gauge wire) and a 20-amp breaker for a 20-amp circuit (12-gauge wire).

Good to know:

ⓘ Breakers protect the branch circuit conductors and wire, not the devices.
ⓘ Wire size determines the max breaker size as follows:

Circuit Ampacity	Minimum Wire Gauge	Correct Breaker Size
15 Amps	14 AWG	15 Amp Breaker
20 Amps	12 AWG	20 Amp Breaker

ⓘ Receptacle, outlets and switches ratings must match the circuit rating (with exceptions for multi-outlet branch circuits).

Related Post: What Happens if You Use a 120V Device on 240V & Vice Versa?

Precautions and Best Practices

Match the breaker to the wire size and intended load.
If you need a 20A circuit, use 12 AWG wire + 20A breaker + 20A receptacles.
If you have a 15A circuit, use 14 AWG wire + 15A breaker + 15A receptacles.
15A breaker on 12 AWG (20A wire) = Safe but not ideal (may cause nuisance tripping).
20A breaker on 14 AWG (15A wire) = Unsafe & violates code.
If you need to replace a breaker, verify the wire gauge and circuit design to ensure compatibility.
Always follow NEC guidelines and consult a licensed electrician for any modifications or if you’re unsure about the circuit’s configuration.

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