Question

Question: Some years back I recall incidents where LED's tripped the circuit breaker if there were "too many" on a circuit.Is this still true?Low many LED's can we really put on a circuit?Is there any "standard", rule of thumb, or any way of knowing?I know that supposedly LED have a big "inrush".In the "old" days we could load up a circuit with fluorescent fixtures to 75% without any issues.How much can we "safely" load up a circuit with LED fixtures? I would like to take advantage of loading up several circuits instead of having to spread them out over many circuits.ThanksRC

Answer 1

Yes, you're right, LED tripping breakers was a known issue, and while significantly better than early LEDs, it's still a factor to consider, especially when maximizing circuit loading. Here's a breakdown

Why LEDs Trip Breakers (The Inrush Current Issue):
Inrush Current (Also Called Inrush or Surge Current)

This is the peak current drawn by an LED driver momentarily when it's first energized. It's MUCH higher than the steady-state running current. Think of it like a water balloon suddenly hitting a wall – a lot of force for a tiny period. This brief surge can trick the breaker into thinking there's a short circuit, causing it to trip. Incandescent and fluorescent fixtures have a lower inrush current.

Capacitive Load

LED drivers (the power supply inside the LED fixture) use capacitors to smooth out the AC voltage. These capacitors act like a momentary short circuit when they first charge up.

Breaker Tolerance

Circuit breakers aren't perfectly precise. They have a tolerance band. Some breakers might trip slightly below their rated amperage, especially as they age.

Is it Still a Problem? Yes, but less so than early LEDs. LED driver technology has improved. Better drivers incorporate inrush current limiting circuitry. However, it's still a consideration. The quality of the LED fixture is a big factor. Cheaper fixtures often have poorer inrush current control. Higher Quality Matters

High-quality LEDs, especially those from reputable brands, are designed with better inrush current limiting.

Larger Installations are More Susceptible

The more LED fixtures on a single circuit, the greater the chance of the accumulated inrush current exceeding the breaker's trip threshold.

How Many LEDs Can You Put on a Circuit? (The Math and Considerations)

This is not a simple "one-size-fits-all" answer. You need to do some calculations, and the steps are as follows:1.

Determine Circuit Amperage

Most residential circuits are either 15 amps or 20 amps. Look at the breaker.2.

Determine Allowable Continuous Load

Important Rule

The National Electrical Code (NEC) generally limits continuous loads (loads that operate for 3 hours or more) to

80% of the circuit breaker's rating. This is a safety factor to prevent overheating. 15 Amp Circuit

15 amps 0.80 = 12 amps maximum continuous load.

20 Amp Circuit

20 amps 0.80 = 16 amps maximum continuous load.
3.

Find the LED Fixture's Wattage and Voltage

Look at the label on each LED fixture. It will state the wattage (e.g., 10W, 15W, etc.) and voltage (usually 120V in North America).4.

Calculate the Running Amperage of EACH Fixture

Use the formula:

Amps = Watts / Volts Example: A 10W LED fixture on a 120V circuit draws 10W / 120V = 0.083 amps (approximately).
5. Calculate the Inrush Current of EACH Fixture (This is the Tricky Part)

Ideally, the manufacturer's specifications will list the inrush current for the fixture. Look for this on the product data sheet, in the installation manual, or on the fixture itself. It might be expressed as "inrush amps," "surge current," or similar. It will also have a duration (usually a fraction of a millisecond). If you cannot find the inrush current specification, this is where you need to make assumptions. A common assumption is that the inrush current can be anywhere from 10x to 100x the running current. A 10x assumption is fairly conservative, while a 100x assumption is a very poor quality driver. A good quality driver should have a small multiple for inrush current.Example Calculations

Let's assume you have 10-watt LED fixtures operating at 120 volts on a 20-amp circuit, and the inrush current is assumed to be 10x the running current. Running Amps per fixture: 10 W / 120 V = 0.083 A Inrush Amps per fixture: 0.083 A x 10 = 0.83AAssuming the inrush current on all lamps occurs simultaneously, which is highly improbable, then we must sum up the inrush amps of the lights to be on the same circuit.Now let's find the number of lights we can put on a single circuit.Since this example circuit is a 20-amp circuit, let's find the number of fixtures that will generate a load of 80% of the maximum amperage, or 16 amps.This is the formula we can use to find the maximum number of fixtures, where N is the number of fixtures:

N  .083 = 16

Then the maximum number of fixtures is:
N = 16/.083N = 192.771
Therefore, you can theoretically put 192 fixtures on a single circuit if it were strictly running amperage being calculated.Next, we must do the same with the inrush amperage, and make sure this circuit can withstand the amperage from the inrush current from each lamp.
N .83 = 16
N = 16/.83N = 19.277
Therefore, the absolute maximum number of fixtures, even with a good driver and inrush current, is 19.However, you must remember that this calculation assumes that all inrush currents will occur at the same time, which is highly improbable.
6.

Start with a Conservative Estimate

I recommend starting with a much lower number than the pure wattage calculation might suggest. For example, on a 20 amp circuit, try installing a few LEDs at a time and testing. If the breaker trips you know you need to reduce the number of fixtures you are installing.

Additional Tips

Use a Clamp Meter to Measure Inrush

A clamp meter (specifically one that can capture peak current) can measure the actual inrush current of your LED fixtures. This will give you far more accurate data than relying on estimates. You clamp the meter around the hot wire feeding the circuit and turn on the lights.

Stagger Start Times (If Possible)

If you have control over the order in which the lights turn on (e.g., with a lighting control system), staggering the start times slightly can reduce the peak inrush current.

Consider Using a "Slow Blow" Breaker (Type D Breaker)

These breakers are designed to tolerate brief surges in current without tripping. However, only use these if you are 100% certain that the wiring is sized correctly for the circuit and that you are not exceeding the safe ampacity of the wiring. These are more common in industrial settings and might not be compatible with your residential panel. Consult an electrician before using these.

Split the Load

If you're having trouble, spread the LED fixtures across multiple circuits. It's the safest solution.

Consult an Electrician

If you're unsure about any of this, or if you're dealing with a large installation, always consult a qualified electrician. They can perform load calculations, measure inrush currents, and ensure your wiring and breaker are adequate for the load.

Check Compatibility with Dimmers

If you are using dimmers, make sure they are specifically rated for LED fixtures. Incompatible dimmers can cause problems, including flickering and premature LED failure.

Fluorescent vs. LED Loading

You're correct that you could often load fluorescent circuits to 75% without issues. Fluorescent ballasts also have inrush current, but typically less pronounced and shorter in duration than older, poorly designed LED drivers. LEDs, if you account for inrush, often allow for more fixtures on a circuit per watt than fluorescents because their running wattage is typically much lower. However, inrush is the key difference.
Bottom Line:While modern LEDs are much better than early versions, inrush current is still a real factor. There is no simple "rule of thumb." You must* consider the inrush current of each fixture, the circuit breaker rating, and the 80% continuous load rule. If you are unsure, consult a qualified electrician. Flag for review

Answer 2

Yes, you're right, LED tripping breakers was a known issue, and while significantly better than early LEDs, it's still a factor to consider, especially when maximizing circuit loading. Here's a breakdown

Why LEDs Trip Breakers (The Inrush Current Issue):
Inrush Current (Also Called Inrush or Surge Current)

This is the peak current drawn by an LED driver momentarily when it's first energized. It's MUCH higher than the steady-state running current. Think of it like a water balloon suddenly hitting a wall – a lot of force for a tiny period. This brief surge can trick the breaker into thinking there's a short circuit, causing it to trip. Incandescent and fluorescent fixtures have a lower inrush current.

Capacitive Load

LED drivers (the power supply inside the LED fixture) use capacitors to smooth out the AC voltage. These capacitors act like a momentary short circuit when they first charge up.

Breaker Tolerance

Circuit breakers aren't perfectly precise. They have a tolerance band. Some breakers might trip slightly below their rated amperage, especially as they age.

Is it Still a Problem? Yes, but less so than early LEDs. LED driver technology has improved. Better drivers incorporate inrush current limiting circuitry. However, it's still a consideration. The quality of the LED fixture is a big factor. Cheaper fixtures often have poorer inrush current control. Higher Quality Matters

High-quality LEDs, especially those from reputable brands, are designed with better inrush current limiting.

Larger Installations are More Susceptible

The more LED fixtures on a single circuit, the greater the chance of the accumulated inrush current exceeding the breaker's trip threshold.

How Many LEDs Can You Put on a Circuit? (The Math and Considerations)

This is not a simple "one-size-fits-all" answer. You need to do some calculations, and the steps are as follows:1.

Determine Circuit Amperage

Most residential circuits are either 15 amps or 20 amps. Look at the breaker.2.

Determine Allowable Continuous Load

Important Rule

The National Electrical Code (NEC) generally limits continuous loads (loads that operate for 3 hours or more) to

80% of the circuit breaker's rating. This is a safety factor to prevent overheating. 15 Amp Circuit

15 amps 0.80 = 12 amps maximum continuous load.

20 Amp Circuit

20 amps 0.80 = 16 amps maximum continuous load.
3.

Find the LED Fixture's Wattage and Voltage

Look at the label on each LED fixture. It will state the wattage (e.g., 10W, 15W, etc.) and voltage (usually 120V in North America).4.

Calculate the Running Amperage of EACH Fixture

Use the formula:

Amps = Watts / Volts Example: A 10W LED fixture on a 120V circuit draws 10W / 120V = 0.083 amps (approximately).
5. Calculate the Inrush Current of EACH Fixture (This is the Tricky Part)

Ideally, the manufacturer's specifications will list the inrush current for the fixture. Look for this on the product data sheet, in the installation manual, or on the fixture itself. It might be expressed as "inrush amps," "surge current," or similar. It will also have a duration (usually a fraction of a millisecond). If you cannot find the inrush current specification, this is where you need to make assumptions. A common assumption is that the inrush current can be anywhere from 10x to 100x the running current. A 10x assumption is fairly conservative, while a 100x assumption is a very poor quality driver. A good quality driver should have a small multiple for inrush current.Example Calculations

Let's assume you have 10-watt LED fixtures operating at 120 volts on a 20-amp circuit, and the inrush current is assumed to be 10x the running current. Running Amps per fixture: 10 W / 120 V = 0.083 A Inrush Amps per fixture: 0.083 A x 10 = 0.83AAssuming the inrush current on all lamps occurs simultaneously, which is highly improbable, then we must sum up the inrush amps of the lights to be on the same circuit.Now let's find the number of lights we can put on a single circuit.Since this example circuit is a 20-amp circuit, let's find the number of fixtures that will generate a load of 80% of the maximum amperage, or 16 amps.This is the formula we can use to find the maximum number of fixtures, where N is the number of fixtures:

Topic: Can "too many" LED fixtures on a circuit trip the breaker?