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How Much is Safe To Run Off Of One Circuit Before It Overloads?


Installing a new appliance or have several things you need to plug in an area of your house or business? Have you ever considered how much the circuits in your electrical system can handle? Do your breakers keep popping? Overloading what your circuits can handle is a safety hazard! Use this guide to better understand your electrical circuits and how to better plan your electrical usage.


How much you can plug into a single outlet depends on the circuit's capacity and how many outlets get their supply from the circuit. Unless you know the capacity of your home's circuits, it's safest to either assume that you have 15-amp circuits. Otherwise, you can call an electrician to check. To begin this guide it's important to learn how they work in your home or business. So lets start there...


Learn How Circuits Work in Your Home or Business

The nerve center of your electrical system is the main panel, usually a gray metal box about the size of a cookie sheet, that typically sits in some obscure spot in a utility room, garage or the basement. Three large wires from the utility company feed the main panel. Although you might spot the wires outside if they’re overhead, they’ll be encased in conduit inside for safety.

Circuit Breaker
Circuit Breaker

Circuit breakers (or fuses) in your main panel limit the power to a level that your wiring system can safely handle and funnel that power through branch circuits, the wires that run to various parts of your house.


If you turn on too much stuff and the power demand on any one circuit exceeds the limits of the circuit breaker (or fuse), the breaker snaps open and shuts down the entire circuit, serving you notice that you have an overload or some other problem.


At first glance, the spider web of cables that spreads out from your main panel might look impossibly complex. Fortunately, the National Electrical Code (NEC) imposes a kind of circuit logic that simplifies the system. The circuits in the main panel are roughly divided into two typesDedicated and General Purpose.

Dedicated Circuit

DEDICATED CIRCUITS serve single large-draw appliances like the furnace, range, built-in microwave, etc. Most of these should be labeled at the main panel, although they often aren’t. And don’t be surprised if you find other outlets on these circuits in older and remodeled homes. Over the years the NEC has gradually increased the number of dedicated circuits, as electrical appliance use has grown.


GENERAL PURPOSE CIRCUITS on the other hand, serve multiple outlets such as lighting and most of the rest of the receptacles in your home. Normally, you can tap into one of these circuits when you need extra power or want to add another outlet. But not always. If you’re adding a receptacle for a high-power use device such as an air conditioner or electric heater, you might have to run an entirely new circuit.


Ok I Understand What an Electrical Panel, Circuit Breakers, & What Types of Circuits There Are What Now?


Well, now you need to know what outlets and appliances belong to each of your circuits! If you are lucky enough to have your circuits already well mapped in your electrical panel you are ready to judge your circuits capacity, otherwise you will need to find what powers what before estimating your power capacity.


How to Find and Map Circuits

How to Find a Circuit

You can do this by yourself or hire an electrician to help.


To DIY simply see what loses power when you turn off a circuit breaker.

Some things are pretty easy, very high power devices like air conditioners, electric ovens, and electric dryers, and electric water heaters will be relatively few and they will be double pole (240 v) breakers.. You can turn each one off and then see whether the oven still works and so forth. Most electric water heaters do not have lights to tell you they are on, so you may need to conclude that is the only unidentified double pole breaker.

You can identify outlets and things that have outlets, like the dishwasher (usually) by using a circuit tracer. These are $20 at the home center and quite useful. You plug half of it into an outlet (that is turned on at any switches!) and then you can find the breaker by running the sensor thingy down the panel.

This will inevitably leave some things unidentified. These may be lights that don’t have outlets that are switched, or hardwired appliances like some dishwashers, or air conditioning air handlers or maybe the furnace.

Those you can track down by plugging in a circuit tracer device into a light-socket-to-outlet adapter (for lights) or by turning them off one by one and running around to see what doesn’t work.


After Our Circuits Are Mapped We Can Judge the Capacity of Our Circuits to Prevent Overload or Get Prepared for Installing a New Appliance


How to Evaluate Your Electrical Load Capacity

Wired For Success Electrical Panel

So here is where we finally find out how much is safe to run off one circuit. Every circuit breaker has a specified amperage (amount of current). This rating is labeled on the breaker itself. The standard for most household circuits are rated either 15 amps or 20 amps. An important note to remember is that circuit breakers can only handle about 80% of their overall amperage. That means a 15-amp circuit breaker can handle around 12-amps and a 20-amp circuit breaker can handle about 16 amps.


STEPS:

  1. First, find the breaker that correlates to the electrical device you are using or intending to use (This is normally either a 15-amp or 20-amp circuit).

  2. Multiply the amperage by 0.8. This is because a circuit breaker should never exceed 80% of its max amperage. Not doing this could leave room for calculation errors, or even worse – electrical fires!

  3. Calculate the amperage draw of ALL the devices you wish to plug into the circuit.

Determining The Number of Devices Your Circuit Breakers Can Handle


It’s very important to understand how much amperage your electrical device draws before installing them into your breaker box. Whether you’re looking to install a heater, AC unit, light switch, or GFCI outlet, there are a few steps you must take.

STEPS:

  1. Check the wattage (max power rating) on your device. This is usually labeled somewhere on the back of the device.

  2. Measure the voltage on the circuit you wish to install your electrical devices. Most household circuits are 120V and larger commercial spaces are 240V (5). If you’re not sure, use a multimeter to test the voltage of your breaker (5).

  3. To calculate amperage, use the equation Amps = Watts/Volts. For example, a 200W light bulb on a 120V circuit would draw about 1.67 amps.

  4. Calculate the TOTAL amperage rating of all devices. Make sure they DO NOT exceed 80% of the breaker’s total amperage.

Power Required for Household Appliances and Applications

(measured watts unless otherwise noted)

  • Electric Range 5,000 (240 volts)

  • Electric Dryer 6,000 (240 volts)

  • Space Heater 1,000 and up

  • Clothes Washer 1,150

  • Furnace (blower) 800

  • Microwave 700–1,400

  • Refrigerator (not required) 700

  • Freezer (not required) 700

  • Dishwasher 1,400

  • Central Vacuum 800

  • Whirlpool/Jacuzzi 1,000 and up

  • Garbage Disposer 600–1,200

  • Kitchen Countertop (two circuits): Toaster 900

  • Coffee maker 800

  • Toaster oven 1,400

  • Bathroom: Blow dryer 300–1,200

Solutions to Overloaded Circuits

How to Prevent Overloaded Circuits

The immediate solution to an overload is simple: Shift some plug-in devices from the overloaded circuit to another general-purpose circuit. Then, flip the circuit breaker back on or replace the fuse and turn stuff back on.

In practice, however, it isn’t so easy to know that you’ve found a good, long-term solution. First you have to locate outlets on another general-purpose circuit. Then you have to find a convenient way to reach it. Resist the temptation to solve the problem with an extension cord. Extension cords are for short-term use. They’re not to be used as permanent wiring or fastened into place.


Circuit breakers in your electrical panel are considered "Safety buffers." Their job is to disconnect from power when they detect the passing current exceeds its amperage. When you don't measure your circuit breaker's load capacity, you run the risk of damaging your appliances, or worse…setting your building on fire!

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