What happens if you put a 15 amp outlet on a 20 amp circuit?

Putting a 15 amp outlet on a 20 amp circuit is generally not recommended, but is allowed by electrical code under certain circumstances. While it may seem harmless, there are some important factors to consider before doing this.

Quick Answer

The quick answer is that a 15 amp outlet contains a 15 amp receptacle, which is only rated to safely deliver 15 amps of current. If installed on a 20 amp circuit, it could potentially be overloaded beyond its rating if a high enough load is plugged into it. This poses a fire hazard due to overheating. However, code does allow 15 amp receptacles on 20 amp circuits in some cases, which we’ll explain more below.

Background on 15 Amp vs 20 Amp Outlets and Circuits

First, let’s provide some background on the difference between 15 amp and 20 amp electrical systems in a home:

• A 15 amp circuit has a 15 amp circuit breaker, and uses 14 gauge wire. It can deliver a maximum of 15 amps (1800 watts at 120 volts).
• A 20 amp circuit has a 20 amp circuit breaker, and uses 12 gauge wire. It can deliver a maximum of 20 amps (2400 watts at 120 volts).

The outlets and receptacles installed on a circuit are rated to the same ampacity:

• A 15 amp receptacle has a T-shaped neutral slot. It is rated for 15 amps.
• A 20 amp receptacle has a neutral slot that is the same size as the hot slots. It is rated for 20 amps.

The general rule is that the ampacity of all parts of an electrical system should match to avoid overloading. So 15 amp receptacles should be installed on 15 amp circuits, and 20 amp receptacles should be installed on 20 amp circuits. If a 20 amp receptacle is installed on a 15 amp circuit, it is underutilized. If a 15 amp receptacle is installed on a 20 amp circuit, it poses an overload risk.

Why Would Someone Put a 15 Amp Receptacle on a 20 Amp Circuit?

There are a few reasons why someone may install a 15 amp receptacle on a 20 amp circuit, even though it goes against proper matching of ampacities:

• Convenience – 15 amp receptacles are more widely available and less expensive than 20 amp receptacles.
• Grandfathering – The circuit may have been upgraded from 15 amps to 20 amps, without changing out the existing receptacles.
• Unawareness – The installer may not understand the importance of matching ampacities.
• Lower loads – The outlets are only expected to serve smaller loads that don’t exceed 15 amps.

Is it Allowed by Electrical Code?

The National Electrical Code (NEC) does allow 15 amp receptacles on 20 amp circuits in certain cases, but with restrictions:

• Only one 15 amp receptacle is permitted on a 20 amp small appliance branch circuit (circuits powering outlets in kitchens, dining rooms, bedrooms, etc).
• A 15 amp receptacle is permitted on a 20 amp circuit only if there are two or more outlets on the circuit. This ensures no single outlet takes the full 20 amp load.
• The 15 amp receptacle must be marked with the word “15A” to identify the ampacity.

However, any outlets that may serve major appliances or high loads like refrigerators or window AC units must be 20 amp receptacles.

Dangers and Risks

While the NEC does permit 15 amp receptacles on 20 amp circuits to an extent, there are still risks:

• If multiple high-load appliances are plugged into 15 amp outlets on the same circuit, the total load could exceed 15 amps, overloading the receptacles.
• The circuit breaker is sized for 20 amps and may not trip if a receptacle is overloaded, creating a fire hazard.
• There is potential for confusion for homeowners, who may not realize the outlets are only rated for 15 amps on a 20 amp circuit.

For these reasons, many electricians recommend avoiding the practice even if technically allowed, and only installing receptacles matched to the circuit ampacity.

Tips for Adding a 15 Amp Receptacle to a 20 Amp Circuit

If you do need to add a 15 amp receptacle to an existing 20 amp circuit, here are some tips to do so safely:

• Only install one 15 amp receptacle per circuit, with all other outlets being 20 amp.
• The 15 amp receptacle should not serve any major appliances.
• Mark the 15 amp receptacle with a special color and the word “15A” for identification.
• Make sure the 15 amp receptacle has a T-shaped neutral slot, not a full neutral slot.
• Balance high loads across multiple outlets instead of overloading one 15 amp receptacle.

Upgrading 15 Amp Outlets to 20 Amp

The best practice is to replace any 15 amp receptacles on a 20 amp circuit with 20 amp receptacles, to fully match the circuit ampacity. This may involve:

• Changing out the 15 amp receptacle for a 20 amp receptacle.
• Replacing the 15 amp outlet box with a larger 20 amp outlet box.
• Using 12 gauge wire pigtails to connect to the existing 20 amp circuit wiring.

Hiring an experienced electrician to perform the upgrades is highly recommended, as they can ensure the work is done properly and safely.

Conclusion

While permitted in some cases, installing a 15 amp receptacle on a 20 amp circuit is not generally recommended, and poses some risk of overloading. It is safer to install receptacles that are properly rated for the circuit amperage. If mixing ampacities, great care should be taken to balance loads, mark receptacles, and prevent misuse that could result in a fire hazard. Consult a qualified electrician if you have any doubts.

Circuit Amperage	Breaker Rating	Wire Gauge	Outlet Rating
15 amp	15 amp	14 gauge	15 amp
20 amp	20 amp	12 gauge	20 amp

This summarizes the proper matching of circuit amperage, breaker size, wire gauge, and receptacle amp rating.

Example Wattage Loads for 15 vs 20 Amp Circuits

To illustrate the difference in capacity, here are some example wattage loads that can be served by 15 amp vs 20 amp circuits:

15 Amp Circuit (1800W Max)	20 Amp Circuit (2400W Max)
1000W space heater 1200W hair dryer 700W microwave	1800W window AC unit 1500W portable heater 1200W coffee maker

Heavy appliances like AC units and large heaters may overload a 15 amp circuit, demonstrating the need for 20 amp circuits for those loads.

Typical Devices and Whether They Require 15 or 20 Amp Circuits

Device	15 Amp	20 Amp
Lighting	X
Small Kitchen Appliances	X
Electric Oven/Range		X
Central AC		X
Major Appliances		X
Space Heaters	X

This gives a general overview of which household devices call for each circuit ampacity based on their power demands.

Quick Reference: Matching Ampacity for Safe Electrical Wiring

Circuit Breaker	Wire Gauge	Outlets
15 amp	14 gauge	15 amp
20 amp	12 gauge	20 amp

Follow this matching of breaker size, wire gauge, and outlet amp rating for safe electrical installations.

FAQs

Is it okay to put a 15 amp breaker on a 20 amp outlet?

No, this would create a mismatch in ampacity. A 15 amp breaker does not provide enough overcurrent protection for a 20 amp receptacle. All components should be matched to avoid overloading.

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

No, the 15 amp wiring is not rated to safely handle 20 amps. This could cause the wire to overheat. The breaker must match the wire gauge and receptacles.

What’s the difference between a 15 amp and 20 amp outlet?

A 15 amp outlet has a T-shaped neutral slot while a 20 amp outlet has a full neutral slot the same size as the hot slots. The 20 amp outlet is rated for the higher amperage of a 20 amp circuit.

Why are some circuits 15 amp and some 20 amp?

15 amp circuits are used for general lighting and receptacle loads. 20 amp circuits are required for larger appliances like dishwashers, microwaves, and laundry machines that draw over 15 amps. Heavier loads require 20 amp circuits.

Can I upgrade a 15 amp circuit to 20 amps?

Yes, but you must replace the 15 amp breaker with a 20 amp breaker, and replace the existing 14 gauge wire with 12 gauge wire rated for 20 amps. You should also replace any 15 amp receptacles with 20 amp receptacles.

Key Takeaways

• Putting a 15 amp receptacle on a 20 amp circuit is generally not recommended but is allowed in certain cases per NEC.
• A 15 amp receptacle poses a risk of overloading if high wattage appliances exceed 15 amps on the circuit.
• No more than one 15 amp receptacle is permitted on a 20 amp small appliance branch circuit.
• The receptacle amp rating should match the circuit for safety – 15A on 15A circuit, 20A on 20A circuit.
• Upgrading wiring and outlets to match is recommended to avoid mismatches.