Every lighting circuit in a property has a chosen maximum capacity defined by its amperage. This means that any combination of light fixtures and bulbs must not exceed the amperage to avoid issues such as flickering, dimming or even tripping of the circuit breaker due to an overload.
When calculating how many lights can be on a 20 amp circuit breaker, you must ascertain the wattage of all the lighting vs the safe and reliable capacity of the circuit.
Let us show you how with a simple step by step guide.
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The number of lights on a 20 amp circuit in the USA is calculated by the total wattage of all the lighting being no more than 1920 watts, which is the derated total at 80% of a possible 2400 watts.
Using a 12 watt LED light, it could in theory have 160 lights on a 20 amp circuit. (1920W divided by 12W)
Using the formula volts x amps = watts there is a simple process to follow.
To calculate how many watts on a 20 amp circuit breaker, multiply the voltage of your lighting circuit (which is the USA is 120 volts) by the amperage of your lighting circuit, which in this case is 20.
120V x 20A = 2400 Watts
Best practice electrical installations design maximum capacities of lighting circuits to use 80% of it’s potential.
80% of 2400 watts is 1920 watts
What lighting is planned for that circuit?
As incandescent light bulbs are being phased out due to their high energy usage, more eco-friendly lighting systems such as LED are becoming the norm. Varying in wattage between 40 and 100 watts each.
Halogen bulbs are a great substitute for traditional incandescent lighting, offering high-quality illumination but with slightly lower energy costs. Founded on the tungsten filament system, these bulbs have improved luminosity thanks to the presence of halogen gas and come in wattages ranging from 35 to 50 watts each.
While fluorescent lighting may still be energy efficient in the long-term, its color temperature and maintenance costs make it a less desirable choice when compared to LED. On average, these lamps are rated between 8 watts to 40 watts.
LEDs, or light-emitting diodes, are the newest form of energy efficient lighting with a multitude of advantages. Not only do they run cooler than halogen bulbs but also consume significantly less electrical power. LEDs can range from 2 watts to upwards depending on your needs.
Option 1: Mixed Wattage Lights
You may be using a number of types of light, which in this case combine each light bulb and light fixture’s power consumption by adding up the wattages on that circuit.
Calculate the capacity by adding up the wattage of all your lights and do not go over 1920 watts, which if you are using LED will give you the option for a lot of lighting.
Option 2: Single Type of Light
If a single variety of bulb or fixture is being used, you can divide the wattage of the bulb or fixture into the derated total capacity to understand how many lights you can have on that circuit.
Using a 12 watt LED light, it could in theory have 160 lights on a 20 amp circuit. (
1,920 watts/12 watts (per bulb) = 160 lights
Electrical derating is essential to prevent circuits from being overloaded, but certain LED light fixtures may cause a momentary surge of current that can exceed the circuit breaker’s capacity and trigger it to trip.
To compensate for this, the total loading of the circuit has to be further derated according to each manufacturer’s recommendations. This is not usually applicable to most LED bulbs.
Using a 80% derating on a 120V circuit, no more than 38 lights should be used.
No more than 19 lights should be used using the recommended 80% derating on a 120V circuit.
Using a 80% derating on a 120V circuit, a maximum of 240 bulbs can be used.
The wattage of a 20 amp 240V circuit is 4800 watts.
To calculate multiply the voltage of your lighting circuit (which is the EU, UK & Australia is 240 volts) by the amperage of your lighting circuit, which in this case is 20.
240V x 15A = 4800 Watts
We also look at How Many Light Can Be On a 15 amp circuit.
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