Home > Electrical Wiring > How to Find Power, Voltage & Ampere Rating of Outlet, Receptacle and Plugs

Basic Concepts Control Electrical Design Electrical Wiring How To Lighting Measuring Instruments Protection

How to Find Power, Voltage & Ampere Rating of Outlet, Receptacle and Plugs

Power, Voltage and Current Rating of Outlet, Switch & Plug

3 14 minutes read

How to Find the Voltage, Power and Ampere Ratings of Outlet, Switch, Receptacle, Socket and Plugs etc.?

Switches, outlets, plugs, receptacles, connectors, breakers, GFCI, RCD’s etc., are designed and rated with various electrical characteristics. The rating of an outlet and switch depends on multiple factors, such as the material and insulation class used for the switch contacts, the size and spacing between the contacts, and the specific application.

There are three main ratings of outlet, switches and plugs:

Current Rating: The current rating, indicated in amperes on the switch nameplate, shows the maximum amperes the switch can safely carry to the connected load circuit.
Voltage Rating: This is the maximum voltage at which a switch can be safely used and installed in a circuit.
Power Rating: It shows the maximum wattage rating of outlet, switch or plug which they can hold and handle safely.

Now, let’s explore the rules and regulations regarding switch ratings and how to select the proper size of a switch based on power, current and voltage capacity.

Related Post: How to Find the Proper Size of Circuit Breaker? Breaker Calculator & Examples

Ratings of Standard Outlets and Switches

US & CA

In the United States and Canada, the most common ampere ratings for electrical outlets in residential applications are 15A and 20A, operating at standard voltages of 120V and 240V single-phase AC. Examples of 15A are NEMA 14-15R, 5-15R, 6-15R and 14-50R etc. Example of 20A outlets are NEMA 2-20R, 5-20R, 6-20R, 14-20R.

Both 15A and 20A outlets are used in 120V and 240V circuits.
- A 15A outlet at 120V can handle 1,800 watts, and 3,600 watts at 240V.
- A 20A outlet at 120V can handle 2,400 watts, and 4,800 watts at 240V.
A 15A outlet and switch are typically used for small appliances and non-continuous loads in bedrooms and general areas, such as lighting and electronic devices (e.g., TVs).
A 20A outlet and switch are used for heavy-duty appliances in kitchens (e.g., microwaves), as dedicated circuits for single devices, and for power tools and appliances in locations such as laundry rooms, garages, and bathrooms.
The suitable wire size for 15A outlets is #14 AWG, while #12 AWG is used for 20A outlets, as per NEC Table 310.15(B)(16).

Good to Know:

According to the National Electrical Code (NEC) 210.19(A), only 80% of the rated outlet, switch, or breaker capacity should be used for continuous load circuits (which last for 3 hours or more).

Thus:

A 15A outlet can be used for 12A of continuous load and 15A for non-continuous load.
A 20A outlet can handle 16A for continuous load and 20A for non-continuous load.

Warning

It is allowed by code to wire a 15A outlet or switch to a 20A breaker.
However, it is against code to wire a 20A outlet or switch to a 15A breaker.

Related Post: How to Wire an Outlet Receptacle? Socket Outlet Wiring Diagrams

In the United Kingdom, the standard ampere rating for electrical socket outlets in residential applications is 13A at 230V single-phase AC. Such example outlet and plug is BS 1363 where the wire size is 1.5 mm² or 2.5 mm² based on the load circuit.

A 13A socket, plug, and switch at 230V can handle up to 2,990 watts, which is sufficient for powering domestic appliances in a typical household.

In Europe and other IEC-compliant countries, the standard ampere rating for electrical socket outlets in residential applications is 16A at 230V single-phase AC.

A 16A socket, plug, and switch at 230V can handle up to 3,680 watts, which is enough to power household appliances in a residential unit.

AUS/NS

In Australia and New Zealand, the standard ampere rating for electrical socket outlets in residential applications is 10A at 230V single-phase AC.

A 10A socket, plug, and switch at 230V can handle up to 2,300 watts, which is enough to supply power to most common household appliances.

Related Post: How to Find The Suitable Size of Cable & Wire ? – Solved Examples

Current Rating of Outlets and Switches

All switches, outlets, receptacles, plugs, connectors, breakers, wires, etc., have two amperage ratings: the maximum current rating and the safe maximum current rating.

Maximum Current:

A switch or outlet can be used at its maximum amperage rating for non-continuous load circuits, such as lighting points. For instance, a 15-amp switch or outlet is rated for a maximum of 15 amps, meaning it can be wired and installed for a 15A non-continuous general lighting circuit.

The maximum current rating depends on the circuit voltage and should never be exceeded. If it does exceed the rated current, the switch’s contacts may melt and weld together, rendering the switch unusable. Without a breaker, this can also damage connected devices and potentially cause a fire. In simple terms, a 15A switch or outlet should not be used to handle a 20A load.

Typically, residential devices run on 15A (14-gauge) circuits, but occasionally, 20A (12-gauge) devices are used with a single-phase 120V AC supply. For 240V AC supply, 30A (10-gauge) circuits are commonly used, depending on the device wattage, such as water heaters.

Most residential devices are 15A, though occasionally, a 20A device may be used.

Safe Maximum Current:

A switch or outlet can safely carry 80% of its rated current for continuous loads, such as water heaters, as per NEC 210.19(A). For example, the safe maximum current of a 20-amp switch or outlet is 16 amps, meaning it can be wired and installed for a 16A continuous load circuit.

Safe Current Calculation:

Safe Maximum Current = Maximum Current × 80%

Related Switch Wiring Tutorials:

How To Wire Switches In Series?
How To Wire Switches in Parallel?

Example:

What is the safe maximum current for a 15A switch?

Solution:

Safe Maximum Current = Maximum Current × 0.8
Safe Maximum Current = 15A × 0.8
Safe Maximum Current = 12A

This means a 15A switch can safely handle a 12A load. Although it can carry a 15A load for non-continuous use, for continuous loads, a 15A switch should only carry a maximum of 12A.

If the current rating is the same for both 120V and 240V, the power in volt-amperes (VA) or watts (W) will differ. For example:

A 20A, 120V switch with a safe maximum current of 16A can handle a load of 16A × 120V = 1,920W.
At 240V, the same switch can handle 16A × 240V = 3,840W.
(Note: This is an example calculation. For 240V supply, use 30A switches, plugs, and outlets.)

Similarly, the safe maximum current for a 15A switch is 12A, and the load it can handle is 12A × 120V = 1,440W.

The current rating of outlet and switch is usually printed on the back. It can also be identified by the rated breaker used with the outlet or the wire size. Additionally, the physical appearance of outlets can help distinguish between them; for example, a 120V outlet typically has two vertical slots, while a 240V outlet has one T-shaped slot in the two vertical slots.

Warning:

15A outlet, GFCI/AFCI, switch etc. can be installed on 15A or 20A breaker in 120V/240V circuits.
20A outlet, switch, receptacles etc. can be installed on 20A breaker, but not on 15A breaker in 120V/240V circuits.

Related Calculators:

Voltage Rating of Outlet and Swatch

Voltage rating of an outlet or switch shows the maximum allowable voltage of the circuit where the switch has to be used for different loads.

A switch can be rated for AC voltage, DC voltage or both having different values and ampacity. For example, a switch can be rated for 240V AC, 230V AC, 15 Amps, 120V DC, 20A etc. The wall switches in the United states are generally rated for 120V to 277V AC. Read the user manual or nameplate data on the switch before installation.

The supply voltage should never exceed the voltage rating of switch. In other words, If we connect an 120V switch on 500V, the applied voltage may jump over the open contacts (and overheat due to overvoltage) of the circuit and connect the load to the supply voltage. It will lead to spark as well which may cause fire. The breaker will open the circuit and stop the operation if current exceed the limit due to excessive voltage as compared to the rated voltage. In short, an 120V and 230V rated switches should not be used for 240 and 480V respective.

Warning:

A switch and outlet rated for:

120V can only be used for 120V circuits.
240V can be used for 120V, 240V but not for 277V (Commercial applications)
120-277 can be used for 120V, 240V and 277V.

Power Rating of Outlets and Switches

The power capacity of a switch and outlet can be calculated using the following formula:

$Watts = Volts \times Amps$

Using this formula,

A 15A outlet at 120V can handle maximum 1,800 watts and safe maximum of 1,440 watts (based on 80%).
A 15A outlet at 240V can handle maximum 3,600 watts and safe maximum of 2,880 watts.
A 20A outlet at 120V can handle maximum 2,400 watts and safe maximum of 1,920 watts.
A 20A outlet at 240V can handle maximum 4,800 watts and safe maximum of 3,840 watts.
A 10A outlet at 230V can handle maximum 2,300 watts and safe maximum of 1,840 watts.
A 13A outlet at 230V can handle maximum 2,990 watts and safe maximum of 23,92 watts.
A 16A outlet at 230V can handle maximum 3,680 watts and safe maximum of 2,944 watts.

Related Post: How to Find the Size of Earth Conductor, Earthing Lead & Earth Electrodes?

How to Find the Rating of an Outlet and Switch?

To find the rating of an electrical outlet, follow these steps:

1. Check the Outlet’s Markings:

Most outlets have their rating information stamped or engraved on the face or back. This typically includes:

Voltage (e.g., 120V, 240V, 230V)
Current (Ampere) rating (e.g., 15A, 20A, 30A)

These markings indicate the maximum load the outlet can handle safely.

2. Examine the Shape and Configuration:

The physical design of the outlet can give clues about its rating:

15-Amp outlets: Usually have two vertical slots with a grounding hole.
20-Amp outlets: Have a T-shaped slot on one side on vertical or horizontal slots to accommodate 20-Amp plugs.

3. Check the Breaker:

The circuit breaker connected to the outlet’s circuit provides insight into the outlet’s rating. If the breaker is rated for 20 Amps, the outlet is likely rated for 20 Amps, unless it was installed incorrectly. Always ensure the outlet matches the breaker’s capacity.

4. Measure Voltage:

Use a multimeter to measure the voltage across the outlet. In the U.S., standard household outlets typically supply 120V, while larger appliances might use 240V outlets. Make sure the outlet voltage matches the expected rating.

5. Wiring and Cable Inspection:

Look at the wiring gauge connected to the outlet. For example:

14 AWG wire is typically used for 15-Amp circuits.
12 AWG wire is used for 20-Amp circuits.
10 AWG wire is used for 30-Amp circuits.

6. Reference NEC Standards:

The National Electrical Code (NEC) has specific guidelines on outlet ratings based on the breaker size and wiring. For example:

15-Amp outlets should be used with 15-Amp circuits.
20-Amp outlets should be used with 20-Amp circuits.

By following these steps, you can determine the rating of an outlet safely and accurately.

Standard & Non Standard Size Outlets and Plugs

US – NEC

The standard outlets and receptacles used for common household applications in the US is 15A and 20A. Here are some common standard and non-standard outlets for both NEC and IEC.

15-amp – NEMA 14-15R, 6-15R, 5-15R, 1-15R – Used for general small household applications.
20-amp – NEMA 14-20R, 6-20R, 10-20R, 5-20R, 2-20R – Used for medium applications e.g. washing machine.
30-amp – NEMA 14-30R, 10-30R, 6-30R, 5-30R, 2-30R – used for dryers
50-amp – NEMA 14-50R, 10-50R, 6-50R, 5-50R, 2-30R – used for over and ranges
60-amp – NEMA 14-60R – Used for HVAC and EV charging stations.

UK and IEC following countries

BS 4573 two pins and and BS 1363 – 3-pins, 13A socket plug and adapters in the UK (IET , BS 7671 and IEC 18th Edition). The non-rewireable plugs are available in 3A, 5A, 10A and 13A.
BS 8546 – Used as travel adaptors compatible with UK plug and socket system.
BS 546 – Used in countries in Asia and Africa electrified by the British.
CEE 7/1, 7/2, 7/4, 7/5 to 7/16 are available in different amperes rating (EN 50075).
Connectors (Male and Female) from C1 to C24 (IEC 60320) and IEC 60906-1 plugs and sockets used in 16 A 250V AC.
AS/NZS 3112 switched 3-pin (10 A) dual socket outlet and plugs (10A) with insulation pin are commonly used for general applications.

For secure and smooth operation, a single outlet should be connected to the 15A circuit.
To know the safe number of socket outlets or receptacles, assign a 1.5A to each one as follow.
20A Circuit / 1.5 A = 13 No of socket outlets and receptacles.
15A Circuit / 1.5A = 10 Number or receptacles or socket-outlet.

For 15A and 20A circuit, use 14 and 12 gauge wire respectively. In case of outdoor, laundry, kitchen, bathroom or watery areas, it is the code to use GFCI and ground fault interrupting receptacles for maximum protection.

Related Post: How to Find the Number of Outlets on a Single Circuit Breaker?

Sizing ATS and Disconnect Switches

Disconnect Switch Rating

According to the article and section of NEC-430:

The suitable size of disconnect switch should be equal or grater than 115% of the rated motor full load current.
If we consider the HP or Watts rating for disconnect switch, the rated HP (or Watts) of disconnect switch should equal or greater than the rated motor HP or watts at the rated voltage.

Automatic Transfer Switch (ATS) Rating

Example: What is the proper size of ATS for a 210kW, 208V three phase AC supply.

Solution:

Current in three phase AC circuits = I = P / (V × √3
I = 210kW / (208V × 1.732)
I = 583 Amp.

You may use then 600A (three poles) automatic transfer switch for 210kW heating loads.

NEC and IEC Rules about Outlet, Receptacle, Socket and Switches Ratings

Ampere Rating of Outlet and Receptacle:

The ampere rating of an outlet or receptacle should not be less than the load of the branch circuit, as per NEC 210.21(A) and (B). Refer to Table 210.21(B)(2) and Table 210.21(B)(3) for details.

Maximum Cord and Plug Load:

When a branch circuit supplies two or more outlets/receptacles, the total load on a single receptacle should not exceed the maximum current specified in Table 210.21(B)(2).

Receptacle Ratings:

When connected to a branch circuit supplying two or more receptacles or outlets, the receptacle’s rating must not be less than the branch circuit rating, as specified in Table 210.21(B)(3).

Receptacle Ratings for Ranges:

The ampere rating of a receptacle used for a range must comply with the demand load specified in NEC 220.55 for a single range.

Wire Gauge for Switches, Plugs, and Outlets:

- Use 14-gauge wire for 15A switches, plugs, or outlets, typically for household lighting circuits.
- Use 12-gauge wire for 20A switches.
- Use 10-gauge wire for 30A switches (mostly for 240V circuits) and 30A circuit breakers.

Voltage and Current Compatibility:

- A switch or plug rated for 15A, 120V can be used on a maximum 15A, 120V load circuit.
- A 15A, 120V switch or outlet cannot be used on a 20A, 120V load circuit.
- A 20A, 120V switch can be used on both 15A and 20A, 120V load circuits.
- It is against regulations to use a 120V switch or outlet on a 240V circuit and vice versa.
- A 240V switch can only be used on a 120V circuit if the current rating is appropriate for the load.
- A 120V switch or plug should not be used on a 240V circuit, even if the current rating is suitable.

Switch Wiring:

Switches must be connected to the phase (live or line) wire, meaning only the phase wire should be disconnected through the switch to control the circuit.
It is against regulations to wire the switch on the neutral conductor.

Switch and Circuit Rating Compatibility:

- A switch rated for 15A, 120V can be used on a 20A, 120V circuit from the distribution board.
- A switch rated for 20A, 120V cannot be used on a 15A, 120V household supply circuit.

Plugging Devices into Outlets:

- A 15A device can be plugged into a 20A outlet, but a 20A device cannot be plugged into a 15A outlet.

Switch Ratings:

Using an oversized switch is acceptable, but a switch with a lower rating than the load current may cause the switch contacts to melt.

IP Rated Switches:

For different levels of protection, designers and electricians must select appropriately IP-rated switches according to IEC 60529, such as IP60, IP65, or IP67.

RCD Protection:

It is recommended to limit the number of socket outlets protected by an RCD (Residual Current Device) to 10 outlets per RCD.

Earth Pin Requirement:

Socket outlets must be provided with an earth-pin connection. However, special socket outlets and plugs for SELV (Safety Extra-Low Voltage) systems must not have an earth-pin contact.

Proper Protection:

Each socket outlet must be equipped with proper protection, including shutters and earthing, in compliance with IEC 60364.

Inductive Load Compatibility:

A switch rated for 10A, 120V AC, designed for pure resistive loads, can be used on 6A, 120V AC inductive loads without affecting the switch’s life expectancy (100,000 operations or 25,000 cycles in both cases).

Proper Heights for Installation:

Always use appropriate heights when installing outlets, receptacles, sockets, and switches.

NEC Table 210.21(B)(2) for Receptacle — NEC Table 210.21(B)(2) – Total Cord-and-Plug-Connected Load to a branch circuit supplying two or more receptacles or outlets.

NEC Table 210.21(B)(3) for Receptacle and Outlet Rating — NEC Table 210.21(B)(3) Receptacle Ratings. When connected to a Branch circuit supplying two or more Receptacles or Outlet.

FAQs

Can a 15A Outlet and Switch be Used on 20A Breaker?

Yes. According to NEC Code, It is allowed to use 15-amp outlets and switches on a 20-amp breaker.

Can a 20A Outlet and Switch be Used on 15A Breaker?

NO. It is against NEC Code to use 20-amp outlets and switches on a 15-amp breaker.

Can a 120V Outlet and Switch be Used on 240V Circuit?

Yes. According to NEC Code, It is allowed to use 120V outlets and switches in a 240V supply.

Can a 240V Outlet and Switch be Used on 120V Circuit?

NO. NEC doesn’t allow to to use 240V outlets and switches in a 120V supply.

Safety Precautions

Warning & Precautions

Disconnect the power before replacing, repairing, troubleshooting, maintenance and installation electrical appliances and equipment.
Switches muse be connect through the phase (live or line) wire (NOT ON NEUTRAL). So that, it can control the ON/OFF operation of the circuit by disconnected the line or phase supply.
Use the proper size of cable and wire for electrical wiring installation.
Failure to do so can result in electrical shock, serious injury, fire or even death.
Perform a continuity test for switch terminal before wiring and installation. Use 10 gauge wire for 240V and 12 Gauge for 120V in the wiring installation.
Follow your regional wiring color codes i.e. IEC or NEC.
Please follow the user manual instruction, local area codes or contact a licensed electrician for proper installation.
The author will not be liable for any losses, injuries, or damages from the display or use of this information or if you try any circuit in wrong format. So please! Be careful because it’s all about electricity and electricity is too dangerous.

Resources:

3 Comments

George says:

February 21st, 2020 at 11:36 pm

This is the best site of technology

abiola says:

June 6th, 2020 at 5:36 pm

A switch rated for 15A, 120V can be used on 20A, 120V circuit from the distribution board.
A switch rated for 20A, 120V can’t be used on household 15A, 120V supply circuit.

i think must be vice versa according to this…

15A devices (load) can be plugged into a 20A outlet, but not vice versa.

1. abiola says:
  
  June 9th, 2020 at 5:30 pm
  
  it was just a confusion.
  
  it is clear now, my appreciation to this site.

How to Find Power, Voltage & Ampere Rating of Outlet, Receptacle and Plugs

Power, Voltage and Current Rating of Outlet, Switch & Plug