An electrical load calculation is a way of determining how much power a home or other building needs for everything to work. An electrical load calculation determines what size electrical panel the building needs. The size of an electrical panel is measured in amps, and modern residential panels range anywhere from 100 to 400 amps. Some older homes only have a 60-amp electrical panel, but the National Electric Code now requires all new homes to have at least a 100-amp service panel.
The Importance of Having an Electrical Load Calculation Performed
If you need to replace your electrical panel, the first step is always to have an electrician perform an electrical load calculation. The reason is to ensure that the new panel is large enough and supplies enough amps to meet all of your electrical needs. You’ll also need to have a load calculation performed when installing a new 240-volt circuit, such as for a new central AC system, hot tub, EV charging station, etc. In this case, the load calculation will determine whether your existing panel is sufficient for the new circuit or if you need to upgrade your electrical service.
If your home’s electric service doesn’t have sufficient amperage, you’ll end up having lots of issues like circuit breakers that keep tripping. A panel that is too small can also lead to the main circuit breaker often tripping and shutting off the power to your home. Having too small of a panel and insufficient electric service is also a major safety hazard. If the panel is too small and you have large appliances trying to draw too much electricity, it can lead to the wiring in the panel overheating and potentially starting an electrical fire.
How Electrical Load Calculations Are Performed
Electrical load calculations are quite complicated and something that should always be performed by a licensed, experienced electrician. The first step is to measure the total square footage of your home in order to calculate how much electricity is required for all of the lights and normal power outlets. In most cases, the home’s square footage will be multiplied by three to calculate the total wattage needed for the lights and outlets. However, the electrical load will be slightly higher if the home has lots of additional lighting or lots of exterior lights and outdoor electrical fixtures.
The next thing is to calculate the wattage needed to power all of the small appliance circuits in the kitchen. Most newer homes have one or two small appliance circuits. These are the circuits that supply power to the outlets located above the kitchen countertops that are used for appliances like toasters, coffee makers, can openers, etc. These circuits should be independent, which means they only power those outlets and not the lights in the kitchen or larger kitchen appliances. For each of these small-appliance circuits, there will be an additional 1,500 watts added to the calculation.
The next step is the most difficult, and that is determining the total electrical load for all of the major appliances in the home that are on an independent or dedicated circuit. This includes everything from the microwave and refrigerator to the oven/range, washing machine, dryer, electric water heater, etc. To do this, electricians will need to inspect every appliance to determine how many watts each one uses.
Part of the reason that this step is more difficult is that you need to account for the fact that not every appliance will run at the same time. For this reason, electricians won’t add the total wattage of all major appliances to the load calculation. Instead, if the total power draw exceeds 10,000 watts, they will only add in around 40% of anything over 10,000 watts.
The other reason it’s difficult is that you need to account for both the starting current and the running current of every appliance. The running current is how many watts the appliance uses when running, while the starting current is how many watts it takes for the appliance to turn on. The starting current of the motors in appliances like refrigerators, dryers, etc. is usually three to five times the running current. If you don’t account for the starting current, you’ll usually end up with issues like your lights and TV flickering when any of the major appliances first turn on.
The last step is to add in the total maximum wattage of the HVAC system since it typically uses the most power. This calculation is usually based on the total wattage of the AC unit. However, if the home has an electric furnace, electricians will use its wattage since electric furnaces typically use three to five times as much power as central AC units. Again, electricians will always need to account for the starting current of the HVAC unit and not just the running current.
Once all of the calculations have been performed, electricians can finally determine how many amps the service panel needs to provide. Amps are calculated by dividing watts by volts. Most of the circuits in a home are only 120 volts, but larger appliances like ACs and dryers are always 240 volts and require fewer amps per watt.
How to Know if You Need a Higher Amp Electrical Panel
Unless your home only has a 60-amp service panel, whatever size panel you have will normally be sufficient to meet all of your needs. However, you will often need to switch to a higher amp panel when putting an addition onto your home or if performing a major renovation in an older home. If you currently only have a 100-amp panel, you will almost always need to switch to at least a 150-amp panel if adding a new central air conditioning system to your home unless your home is fairly small.
If you only have a 100-amp service panel and you keep having issues with lights flickering when your AC or dryer comes on, it’s a sure sign that you need to upgrade your electrical service. The reason that your lights flicker in this situation is because the starting current of these appliances draws so much of the available power. This temporarily decreases the current that flows to the other circuits, which can result in some lights dimming or flickering.
Northern California’s Home Service Experts
With nearly 20 years of experience, Huft Home Services is the company to trust for all of your residential electrical, plumbing, heating, and air conditioning needs. Our team of licensed electricians specializes in electrical panel upgrades and can help if you need a load calculation performed. We also install all types of electrical equipment including EV charging stations, generators, and whole-home surge protection, and we can take care of your electrical inspection and repair needs as well. We have locations in Sacramento, Yuba City, and Elk Grove, so give us a call if you need any home service in Northern California.
