Why Wire Gauge Is Important Wire Use Rated Ampacity Wire Gauge Low-voltage lighting and lamp cords 10 amps 18-gauge Extension cords (light-duty) 13 amps 16-gauge Light fixtures, lamps, lighting circuits 15 amps 14-gauge Kitchen, bathroom, and outdoor receptacles (outlets); 120-volt air conditioners 20 amps 12-gauge Click to see full answer. Regarding this, how do you determine the amperage of a wire? Wire Size & Amp Ratings To calculate the load requirement for a circuit, first add up the wattage of all the electrical devices that will be on the circuit. Then, divide the total wattage by the voltage of the system, typically 120 or 240, and that will give you the required current or amps.One may also ask, how many amps will a 18 gauge wire carry? 16 amps In this manner, what size wire is rated for 400 amps? Wire Size and Amp Ratings Wire Size 75°C (167°F) AWG (mm²) Copper 400 (203) 355 500 (253) 380 600 (304) 420 How many amps can a 2.5 mm cable take?A 2.5mm cable is capable of supplying around 23-25 amps depending on the method of installation, so is fine, safe and compliant on a 20amp circuit breaker.