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How to Find the Number of Lights on a Single Circuit Breaker?

How Many Lights Can You Put on a Single Circuit Breaker? – NEC & IEC

Another basic query about the lighting points and fixtures on sub circuits and breakers we receive the most from the readers. We got multiple queries like, how many lights can I put on a 15A circuit breaker? What are the maximum numbers of lighting points that I can connect on a 20A circuit? What is the safest number of lighting fixtures you can connect to a 10A or 16A circuit breaker? Well, don’t worry, we have an explanatory answer (according to NEC & IEC) for all questions mentioned above.

First of all, NEC didn’t mention the exact number of lighting points on a single circuit breaker but it suggests only 80% of the load can be connected on a circuit breaker. For example, 80A load can be connected to a 100A breaker. Similarly, No more than 12A load should be connected to a 15A circuit. Same is the case for IEC where the safety factor of 80% of the total rating of the breaker is applicable for general lighting circuits.

As a general rule of thumb, a total of 8-10 numbers of light bulbs can be installed on a single pole, single phase 15A, 120V circuit breaker. Let’s see the solved example for both 120V and 240/230V circuit breakers as follows.

How to Find the Number of Lights on a Single Circuit Breaker

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Determining the Number of Lights on a Circuit

Example 1: 120V – NEC – US & Canada

How many Lights can I put on a 15A, 120V circuit breaker?

Solution:

Step 1:

First of all, we will find the wattage rating of 15A, 120V circuit breaker as follow:

Wattage = Amperes x Volts

Wattage =  5A x 120V = 1800 Watts

Step 2:

This is the ideal case where a 15A, 120V single pole circuit breaker will handle a total load of 1800 watts connected to it. But NEC suggests only 80% of the load may be installed on a rated breaker as a safety factor or max demand factor in continuous load. This way,

Wattage =  1800 Watts x 0.8 = 1440 Watts

Step 3:

Finally, we can calculate the number of lights by dividing the calculated wattage of the breaker by light fixture wattage. For example, if the wattage rating of light fixture is 80W, then

Max Number of Light Fixtures = 1440 W / 80W = 18

It shows a maximum of 18 lighting points each of 80W can be connected to a 15A, 120V circuit. To be on the safe side, the safest number of lighting points is 80% of the max number of calculated light fixtures.

Safe Number of Lighting Points = 18 x 80% = 14.4

For smooth operation without unusual and unwanted tripping the breaker, it is suggested a total of 14-15 light bulbs can be installed on a 15A, 120V circuit breaker.

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Finding the Number of LEDs  per Circuit

Now what about the number of LEDs bulbs, For example, what is the maximum number of 15W LEDs lights which should be safely connected to a single pole 15A breaker?

Well, we do the same calculation as above (but read the bottom line which shows why we should not do it)

To find the number of LED bulbs, simply divide the calculated breaker wattage by LED wattage e.g.

Number of LED Lamps = 1440 W = 15 W = 96

Ideally, we can connect a huge i.e. 96 numbers of LEDs per circuit rated for 15A, 120V. But it is not recommended to do so. If we connect that huge amount of LEDs on a single circuit breaker, all the light points will stop working at once if a fault occurs on that specific circuit. In addition, It will be hard to troubleshoot the circuit and connected LED’s light in case of fault. So it is better to stick to the general rule of thumb or safest number of lighting points. 

Note: It is recommended to keep at least two lighting circuits in a home because the rest of the lighting points on the second circuit will be operational in case a fault occurs on the first circuit. For detailed analysis and design, check the previous post on the lighting calculations in a building.

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Example 2: 230V – IEC – UK, EU etc.

How many Lights bulbs each of 90W can I connect on a 13A, 230V circuit breaker?

1 – Calculate the Breaker Wattage

Watts = Current x Voltage

Watts = 13A x 230V = 2990 W

2 – Wattage with Safety factor of 80%

= 2990 W x 80% = 2392 W

3 – Divide the calculated breaker wattage by the light Wattage

= 2392 W / 90 W = 26.5

It shows that you may put a maximum of 26 numbers of light bulbs each of 90W on a 13A, 230V single pole, single phase circuit breaker.

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