Home circuits are designed intentionally for use with a particular electrical load within certain safety margins. If you plan to add new lighting fixtures to your home, you need to ensure that you do not overload the circuit. So how do you figure out how many lights you can run on a 15-Amp circuit?
The number of lights that can run on a 15-Amp circuit will depend on the wattage of the lights. The total amperage used by the lights on the circuit must not exceed 80% of the circuit breaker’s rating. For a 15-Amp circuit breaker, this will be a maximum of 12-Amps. Assuming a 60 watt light, you can put up to 24 lights on a 15 amp breaker.
If you are using low-wattage LED bulbs, an LED bulb using 10 watts, you can install up to 150 bulbs on a single circuit. We do not recommend this because you can’t use bulbs other than LED without exceeding the 15 amps and tripping the circuit. However, this is a good illustration of why LED bulbs conserve energy so well.
Keeping the correct load on a circuit is a matter of safety for your home. An overloaded circuit is not only frustrating but poses a fire risk for your home as well. Understanding the basics regarding how much a circuit can handle will give you the safety margins to plan to add new light fixtures in your home. Let’s take a look at exactly how you can determine the capacity of a 15-Amp circuit.
How Much Can A 15-Amp Circuit Handle?
Electrical circuits in your home can only handle a limited electrical load. Outlets requiring similar demand in a room share a circuit.
Grouping lights in your home allow wiring on a separate circuit just as contractors group electrical outlets together.
The number of lights you can run on a circuit varies by the circuit breaker’s rating, thickness or gauge of the wire used in the circuit, and the energy required by the lights.
Homebuilders will use different gauge wires depending on the circuit. The lighting circuit uses a 14-gauge electrical wire, a lighter gauge wire than that used for electrical outlets. Circuits rated for a 20-Amp breaker will generally use a 12 to 10-gauge copper, a thicker copper wire.
Drawing too much current or amperage through a wire will cause the wire to heat up. The thinner the wire, the quicker the wire will heat up when too much current flows through the cable.
Most local wiring codes follow the general guidelines of the National Electrical Code or NEC, with a few minor variances. The NEC states that a circuit breaker load should not exceed 80% of its capacity.
This requirement means that on a 15-Amp circuit breaker, you cannot exceed 12-Amps flowing through the circuit at any one time. There is no formal restriction on the number of light fittings that you can have on a 15-Amp circuit. Still, if all those lights are operational simultaneously and the current exceeds 12-Amps, you will violate the wiring code.
The result is that you should only put the number of light fittings and globe wattage on the circuit that would stay within the 80% limitation if all the lights were on simultaneously.
How Many Lights Can I Put On A 15-Amp Circuit?
As we have already indicated, the number of lights you can put on a 15-Amp circuit depends on the wattage of the lights you use in the light fixtures.
To figure out if you are within the 80% capacity limit of the 15-Amp circuit breaker, you will need to check the wattage of each light on the circuit and do a little math to check your limits.
How Do You Work Out Light Wattage To Amps?
The lights rating is in the unit of Watts, while the rating for circuit breakers is Amps. You must convert the Watts of the lights to the same unit of measure as the circuit breaker to establish your limits for the circuit.
You can quickly establish this limit via a basic equation because the light wattage combines voltage and amperage. In most homes, the voltage used is 120-Volts, but you must substitute your voltage where 120-Volts is used in the equation if your home is different.
The formula for Watts is Watts = Amps X Volts. To reverse the formula to get the Amps, use the following formula.
Amps = Watts / Volts
To determine how many amps a 60-Watt light bulb will draw, plug the values into the equation.
Amps = 60-Watts / 120-Volts
Amps = 0.5
Our result shows that a 60-Watt light will draw a current of 0.5-Amps. We can use this calculation for each of the light circuits in our home to establish if we are within the 80% capacity of the circuit breaker or if we need to install a completely new circuit to add more lights to our home.
Let’s work out a couple more examples of this calculation in action to ensure we are within the limits of our circuit.
How Many 75-Watt Lights Can Be On A 15 Amp Circuit?
If you want to install 75-Watt light bulbs on all your light fittings in a 15-Amp circuit, how many of these 75-Watt lights can you install and still stay within the 80% limitation?
Amps = 75-Watts / 120-Volts
Amps = 0.625
A 75-Watt light will draw 0.625-Amps of current. To establish how many of these lights we can install on the circuit, we need to divide the 12-Amp limit by the Amps used by the light.
12-Amps / 0.625-Amps
= 19.2 of the 75-Watt Lights
This formula shows us that we can install up to 19 of the 75-Watt lights and remain within the 80% limitation of a 15-Amp circuit breaker.
How Many 100-Watt Bulbs Can Be On A 15 Amp Circuit?
We can apply this formula to determine how many 100-Watt lightbulbs we could install on the circuit to stay within the limits required by the wiring code.
Amps = 100-Watts / 120-Volts
Amps = 0.833
A 75-Watt light will draw 0.625-Amps of current. To establish how many of these lights we can install on the circuit, we need to divide the 12-Amp limit by the Amps used by the light.
12-Amps / 0.833-Amps
= 14.4 of the 100-Watt Lights
Once again, the formula shows we can install a maximum of 14 lights rated at 100-Watt and remain within the 80% limitation of a 15-Amp circuit breaker.
What If You Have Mixed Wattage Lights?
We don’t have the same wattage lights throughout our homes in real life, so you need to collect the data for each light on the circuit. You need to establish the Watts of each light on the circuit, work out the amps that each light uses and then add the Amps together.
The total of the Amps used by the lights on the circuit must not exceed the limit of 12-Amps for the 15-Amp circuit breaker.
For example, if you have 2 x 60-Watt Lights, 5 x 75-Watt lights, and 3 x 100-Watt lights on the same 15-Amp circuit, your calculation would look as follows.
1 x 60-Watt = 0.5-Amps, so 2 lights use 2 x 0.5-Amps = 1-Amp
1 x 75-Watt = 0.625-Amps, so 5 lights use 5 x 0.625 = 3.125- Amps
1 x 100-Watt = 0.833-Amps, so 3 lights use 3 x 0.833 = 2.5-Amps
If we add up the current for all the lights we get the following result.
1-Amp + 3.125-Amps + 2.5-Amps = 6.625- Amps Total
Our calculation shows that our total of 6.625-Amps is still well below the 12-Amps allowed on the circuit.
Conclusion
Figuring out how many lights you can run on a 15-Amp circuit is a relatively simple exercise and will give you the means to plan out any extensions you want to make to the electrical circuits of your home.
Should you be in any doubt about your calculations or how to do any maintenance on your electrical circuits, it is always safer to use the services of a qualified electrician. Electricity is dangerous, and it is not worth risking your health and safety and that of your family to save a few dollars.
If you do any DIY electrical work in your home, it would be wise to get an electrician to verify your work before connecting it to the mains supply.
