How Many Lights on a 15 Amp Circuit

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 15 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.

How Many Lights on a 15 Amp Circuit?

The number of lights on a 15 amp circuit in the USA is calculated by the total wattage of all the lighting being no more than 1440 watts, which is the derated total at 80% of a possible 1800 watts.

Using a 12 watt LED light, it could in theory have 120 lights on a 15 amp circuit. (1440W divided by 12W)

How to Calculate How Many Lights on a 15 Amp Circuit

Using the formula volts x amps = watts there is a simple process to follow.

1. Calculate How Many Watts

To calculate how many watts on a 15 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 15.

120V x 15A = 1800 Watts

2. Derate the Circuit Capacity

Best practice electrical installations design maximum capacities of lighting circuits to use 80% of it’s potential.

80% of 1800 watts is 1440 watts

3. Select the Lights

What lights are going on that circuit?

Incandescent light bulbs are fast becoming obsolete as their production is being banned and their high energy consumption is being replaced with more energy efficient lighting such as LED. They range between 40 watts to 100 watts each.

The halogen bulb used a tungsten filament for the light but surrounded it by halogen gas. The incorporation of this gas has enabled greater luminosity and quality in lighting compared to incandescent but with slightly lower running costs. Halogen bulbs are usually rated between 35 watts to 50 watts each.

Fluorescent lighting still offers some energy efficiency and is long lasting, but the color temperature of these lights can make them a less desirable choice and overall including maintenance and running costs, they are less efficient than LED. Fluorescent lamps are usually rated between 8 watts to 40 watts.

LED, or light-emitting diode, lighting is the latest form of energy efficient bulb with the distinct advantages of running cooler than halogen and consuming significantly lower energy levels. LEDs range 2 watts upwards.

4. Formulate How Many Lights Can Be Used

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 1440 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 120 lights on a 15 amp circuit. (

1,440 watts/12 watts (per bulb) = 120 lights

FAQ

Does a 15 Amp Circuit Need Derating for LED Inrush Current?

The derating for a 15 amp circuit is to protect against overloaded circuits, but some LED lights fixtures can create an inrush current that momentarily spikes the loading and trips the circuit breaker.

To compensate for this, the total loading of the circuit has to further derated according to each manufacturer’s recommendations. This is not usually applicable to most LED bulbs.

How Many 50-Watt Lights Can be on a 15 Amp Circuit?

Using a 80% derating on a 120V circuit, no more than 28 lights should be used.

How Many 100-Watt Lights Can be on a 15 Amp Circuit?

No more than 14 lights should be used using the recommended 80% derating on a 120V circuit.

How Many 8-Watt LED Bulbs Can Be On A 15 Amp Circuit?

Using a 80% derating on a 120V circuit, a maximum of 180 bulbs can be used.

How Many Watts on a 15 Amp 240V Circuit?

The wattage of a 15 amp 240V circuit is 3600 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 15.

240V x 15A = 3600 Watts

We also look at How Many Light Can Be On a 20 amp circuit.

Andrew Orange, the owner of Orange Lighting qualified and worked as an interior designer in 1993 before specialising in lighting working on high profile projects based in London. Since starting Orange Lighting Ltd in 2003 he has been sharing his knowledge and unique teaching style mostly to his designer clients, offering practical real life advice born from running a busy consultancy and lighting supply business. Launching in 2020, his blog has evolved into Quick & Easy Lighting, curating some 25 years design experience into making the lighting choice and design process achievable and easy to understand for all.