When it comes to electrical load capacity, there are two schools of thought: those who believe in the “bigger is better” approach and those who think that it’s all about efficiency. The truth, as is often the case, lies somewhere in between. Electrical load capacity refers to the amount of power that an electrical system can safely handle without overloading or damaging the system.
The load capacity of an electrical system is determined by a number of factors, including the size and type of wire used, the number of breakers and fuses, and the overall design of the system. In general, households with more appliances and higher wattage needs will have a higher load capacity than those with fewer appliances and lower wattage needs. However, it’s also important to consider how efficiently the system is being used. An electrical system that is constantly being taxed to its full capacity will degrade more quickly than one that isn’t being used as intensively. As such, it’s important to strike a balance between appliance needs and efficiency when determining electrical load capacity.
What Is Amp?
In order to understand amps, it is first necessary to understand electricity. At a basic level, electricity is the flow of electrons through a conductor. The rate of flow is measured in amperes, which is why an amp is often informally referred to as a “current.” In layman’s terms, amps are a unit of measurement for the amount of electricity that flows through a specific area per second. The more amps that flow through a conductor, the more electrical power is generated.
What Is Voltage?
A voltage is like a pressure difference. You can think of it as the difference in water pressure between two different points in a pipe. The higher the difference in height, the greater the pressure. In an electrical circuit, voltage is the difference in charge between two points. The higher the voltage, the more potential energy there is to do work, like powering a light bulb. Voltage is measured in volts (V).
Amperage is the standard unit of measurement for an electrical system’s total capability (amps). In very ancient houses, the original electrical supply may only provide 30 amps. Homes that are slightly newer may have 60-amp service (constructed before 1960). The normal size of a home’s electrical service in structures built after 1960 is 100 amps. However, these days new constructions often have at least a 200-amp service, and many even have 400-amp installations. Properties having square footage of more than 10,000 square feet often have 800 amp services installed.
If you plan on wiring an outlet or light fixture onto an existing electrical circuit you will have to determine if the circuit has enough capacity to handle the additional load.
Start by adding up the total wattage that is currently being consumed on the circuit you want to add to. If you don’t know what is powered by the circuit in question, switch it off at the breaker box and then turn lights and electrical appliances on and off throughout the house. If the item doesn’t turn on then you know it is part of the circuit.
Since you probably don’t have the operator’s manual for every electrical appliance you ever bought, it may be difficult to determine how much wattage each item consumes. For that reason, you can use this handy wattage calculator to help find your total. Be sure to include wattage for appliances that are occasionally plugged into the circuit too, such as a vacuum, or power tool. And, don’t forget to include the wattage for the new fixture you’re adding to the circuit.
Once you have your total wattage figure, check the circuit breaker for its rating. A 15 amp circuit can handle up to 1800 watts and up to 2400 watts on a 20 amp circuit. If the power needed is more than 80% of those numbers you may want to consider a different circuit or running a new circuit. The reason is, that some appliances have to start loads that are 3 times their running load. What this means is, that you plug your circular saw into the new outlet you just installed and when you start it up, your workshop lights go out. That’s because you calculated your total wattage using the running load of each appliance. The high start up load required by the circular saw put too much demand on the circuit which tripped the breaker. For this reason you need that 20% buffer to account for the start up demand from certain appliances.
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Amps = Watts/Volts
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Volts x Amps = Watts
You may use these equations to figure out how much power a circuit needs, how much it uses, and how much power the complete electrical system needs. A 120-volt, 20-amp branch circuit, for instance, can handle a maximum of 2,400 watts of power (20 amps x 120 volts). When the load is no more than 80% of the capacity, as is often recommended, a 20-amp circuit can safely handle just 1920 watts of electricity. If you want to keep this circuit safe from overloads and prevent a fire, don’t use more than 1,920 watts’ worth of lighting and electrical equipment.
Finally, remember to run the correct wiring for your new outlet or light fixture, 14 gauge for a 15 amp circuit and 12 gauge for a 20 amp circuit. Also be aware that by code, you can not add to the circuit that powers the kitchen countertop outlets.