One of the most common problems in household electrical circuits is the overloading of the electrical outlets. The number of electrical outlets on a 15-amp circuit is restricted for safety reasons and according to the maximum loading capacity of 15-amp breakers. So, how many outlets exactly can you have on a 15-amp circuit?
You can install a maximum of 8 electrical outlets on a single 15-amp circuit. The National Electrical Code, or NEC, limits the continuous load capacity to 80% of the rated total load of a breaker. This limitation works out to a general rule of 1 outlet per 1.5-amps of the circuit breaker.
A circuit breaker that keeps tripping indicates that the load on the circuit exceeds the breaker’s capacity. The NEC limits the number of outlets on any circuit, 15-amps or otherwise. Let’s venture into the reasoning behind the number of outlets allowed on a 15-amp circuit and why you should stay within these boundaries.
How Many Outlets Can You Have Per Circuit?
The NEC does not allow for a circuit to run at the total capacity of the circuit breaker continuously because this amount of current going through the wiring all the time can pose some serious safety risks.
Running at total capacity will lead to the wiring in the circuit heating up, resulting in the insulation around wires melting or becoming compromised. The consequence of this is that short circuits can result, causing fire or life-threatening electric shock.
You are allowed to run your circuits for short periods at the maximum capacity of the circuit breaker, but not continuously. Typically, the NEC refers to a short time as being 3-hours or less; longer than this, you will be contravening the electrical code and taking unnecessary risks with your home and your family.
Another reason that the limit is 80% of the total capacity of the circuit breaker is that the NEC accounts for people who overload electrical outlets to increase the number of devices powered from a single outlet.
Using the following formula, you can determine how many outlets you can have on a 15-Amp circuit to stay within the 80% load limit on the circuit.
(15-Amps x 0.8) / 1.5 = 8 Outlets
Some multi-plug or extender plug manufacturers put safety mechanisms into their multi-plugs, but others don’t. These plugs can overload a circuit and break the electrical code by running a continuously higher amperage than the regulated 80% capacity through the circuit breaker.
How to Know You are Overloading the Circuit
Besides the obvious symptom of a frequently tripping 15-amp circuit breaker, how do you know if you overload the circuit with too many devices running simultaneously?
You can ascertain the answer by doing some simple math. The unit Amps equals Watts divided by Volts. In most of our homes, we are running 120-volts AC, so the voltage is known. Use the following formula to determine the maximum number of Watts that we should be running on the circuit.
15-Amps = Watts / 120-Volts
Watts = 15-Amps x 120-volts
Maximum Watts = 1800-Watts
This formula gives us the maximum wattage load for a single circuit. However, we are not allowed to exceed 80% of the capacity of the circuit breaker. You can calculate this as:
1800 x 0.8 = 1440-Watts
Our calculation shows that the maximum wattage on the circuit for an extended time is 1440-Watts. If you add up the watts of every device connected to each outlet on the circuit, the total wattage should be less than 1440-Watts.
Each outlet should not be drawing more than 1.5-Amps of current, so the wattage on each outlet can be determined as follows.
Watts = 1.5-Amps x 120-Volts
Maximum Watts per outlet should be 180-Watts
Exceeding this maximum wattage on an individual outlet will quickly increase the current demand on the circuit breaker above the 80% capacity regulation.
Does 15 or 20 Amp Have More Outlets?
The same principles apply to calculating a 20-Amp circuit. A 20-Amp circuit is simply rated to handle more current throughput than a 15-Amp circuit.
The same 80% of the maximum capacity of the circuit breaker applies to the 20-Amp circuit, which means that the maximum number of outlets that can be on this circuit is 10. Thus a 20-Amp circuit can have more outlets than a 15-Amp circuit.
Using the same rule-of-thumb guideline of 1 outlet for each 1.5-Amps of the circuit breaker rating, you can conclude that:
(20-Amps x 0.8) / 1.5 = 10 Outlets
Can You Have Outlets and Lights on The Same Circuit?
If you add light fittings onto an outlet circuit, you need to diminish the number of outlets you put on the circuit by the number of light fittings you add. For example, if you add two light fittings to a 15-Amp circuit, the maximum number of outlets you can have on the circuit would be 6.
Even though you can add light fittings onto an outlet circuit, it is generally not an accepted practice for the circuit breaker panel’s organizational purposes and safety. It becomes a safety issue if you do not know which outlets and lights are on which circuit.
For this reason, the wiring for houses generally stays with the principle of keeping outlets on one circuit and light fittings on a different circuit.
In certain instances, the NEC’s infringement is to have outlets and lights on the same circuit. For example, in bathrooms and for above-counter outlets in kitchens intended for small kitchen appliances.
While you can wire lights to an outlet circuit, you will need to check the NEC and your regional stipulations for this practice before you implement this configuration. As mentioned, there are limitations to this practice, depending on the room where you want to have this done.
The general feeling is that mixing outlets and lights unnecessarily complicates the wiring system, which is not encouraged.
The number of electrical outlets on a 15-Amp circuit is a maximum of 8 to keep within the restrictions of the electrical code, which states that the circuit breaker should not be operating at more than 80% of capacity.
The same 80% capacity rule applies to 20-Amp circuits, where the maximum number of outlets is 10. If you are concerned that the number of outlets on a circuit is more than these limitations, you should consult a qualified electrician to verify the compliance of your circuit.