Before installing lights, check your circuit breaker capacity and calculate your safe power limit.

Most homes use 15-amp circuit breakers, which you can confirm by checking your electrical panel. You'll typically see a "15" or "20" on the breaker switch, indicating the amperage at which the breaker will trip. Keep in mind that if other lights or electrical appliances share the same circuit, your available amperage will be reduced (unless those devices are turned off).

It's recommended to stay below 70% of the maximum available amperage on the circuit. This safety buffer accounts for electrical fluctuations from rain, initial power surge when plugging in lights, and the gradual increase in power draw as wires and bulbs age.

Now that you know your available power, let's calculate how many lights you can safely install. For example, on a 15-amp circuit with no other devices, leaving a 30% buffer gives you 10.5 amps.
Check your product's power usage—you'll find watts per unit listed on the product or its packaging. To find amps per unit, divide watts by your area's voltage.

Keep in mind that actual power needs aren't just a simple calculation. Wire and plug resistance adds to power consumption, which increases as products age. Let's look at two popular products: the retrofit bulb (G30 or C9) and the lighted string set (C6 or 5mm mini-light).

Each of our G30 and C9 bulbs draws 0.45 watts. To calculate how many you can run on a circuit, you’ll need to convert watts to amps:

0.45W ÷ 120V = 0.00375 amps per bulb

In theory, a 15 amp circuit with a 30% buffer (giving 10.5 amps to work with) could power up to 2,800 bulbs (10.5 ÷ 0.00375). However, that’s not realistic in the field. Long runs of wire—especially 18 AWG—introduce resistance that limits how far power can travel effectively.

Based on our experience, 250 feet of G30 or C9 bulbs typically draws 3.5 to 5 amps, depending on wire age and condition. That means you should be able to hook up 500 bulbs to the circuit described above. However, cable & plug limitations must be considered:

The SPT2 plugs attached to the ends of the wire are rated for 8 amps max. With a 30% safety buffer, your safe operating limit becomes 5.6 amps. That means you should limit each run to 250 feet.

If you have a 15-amp circuit, you can safely install two 250-foot runs. For long installations—like lighting up a shopping plaza roofline—you’ll need at least one outlet every 500 feet.

Our C6 and 5mm mini lights come in two wattages, depending on the color:

For the higher wattage strings (4.8W), use the formula below to calculate amps:

4.8W ÷ 120V = 0.04 amps per string

If you have 10.5 amps available (a 15A circuit with a 30% buffer), that gives you a theoretical limit of 262 strings (10.5 ÷ 0.04). But there’s a more important limitation: the 5-amp fuse in our adapters. These adapters connect to 20 AWG wire, which CSA limits to 5 amps max. Applying a 30% safety buffer reduces that to 3.5 amps, which equals 87 strings max per run (3.5 ÷ 0.04).

In practice, we recommend 75 strings per run to give a little more breathing room. That’s still a 1,875-foot run of wire, which is substantial. For extra safety, CSA recommends no more than 45 strings per run.

Keep extension cord lengths under 100 feet—or under 50 feet when using 18AWG SPT2 cable. Longer cords create more resistance and consume more power. Since the relationship between distance and power consumption isn't linear, you can't simply calculate "x amps per y feet."

In all cases, when you think you're close to your limits, it's a great idea to measure. One of the handiest tools you can keep in your tool kit for troubleshooting is a clamp meter, which is available at most hardware stores. This will give you accurate information that will ensure you're not overloading adapter fuses or electrical circuit breakers.

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