For most of us, our only concern with the electricity in our homes is whether or not we have it. Beyond that it’s a simple question of having enough outlets and “If I unplug this cord will something important shut-off?” But what’s actually happening with the circuitry running behind your walls?Why do lights dim or appliances stop in the summer? Or blackouts occur during storms?

To answer these questions, it’s first important to understand the voltage ranges operating in your home.

And before that even, what is actually meant by the term voltage.

A common analogy used when discussing electric circuits is the comparison to water filled tanks and pipes. In this scenario, an electric current is similar to the flow of the water (measured in Amps), an electric charge is the quantity of water (measured in Coulombs), and voltage is the pressure that pushes the water along – or more precisely, the difference in pressure between two points (measured in Volts).

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Now imagine you have two separate water tanks where the quantity of water (charge) is the same, but the width of the pipes is different.

Because both tanks carry the same amount of liquid, the pressure (voltage) is equal. However, when the water is released the flow (current) in the narrower pipe is less than the wider one.

This means to get the same results with both tanks we’d have to increase the amount of water in the tank with the narrower pipe – which in turn would lead to an increase in pressure.

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This variation is important to understanding how electricity enters and operates in your home.

For example, think of the cord sizes for all of your appliances – now compare the size of your smartphone cord to that of the cord for your dryer. There’s quite a difference, right? The length and width of these cords is similar to the size of the water pipes in the analogy above. Larger items like your dryer or AC unit are going to require a lot more power than your lamp. However, if the initial charge for both is the same, then limiting the size of the cord becomes extra important.

But the width and length of your appliance cords isn’t the only thing regulating the power in your home.

That starts with your circuit breaker box.

How the Electricity in Your Home Works

Voltage

When electricity first enters your home it is routed through your circuit breaker box and split into different voltage ranges.

Every home in the U.S. and Canada operates on a split-phase system, which is composed of 3 wires; two line wires and one ground. This means that while the power that comes into your home is 240V, it is then split at the main circuit breaker into two 120V halves. These halves are then run through one of the line wires and the grounded center, and are used to supply power to your basic appliances like lamps.

For larger appliances like electric stoves or dryers, power runs through both line wires and the ground simultaneously at the full 240V. This allows the system to balance itself between the two when electrical loads increase.

But where do these ranges fit in the bigger picture?

Below we’ve created a simple guide to help you better understand the different voltage ranges and their terminology.

Voltage Ranges in the U.S. and Canada

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Nominal Voltage: This is the standard voltage produced by a utility company.

Rated Voltage: This is the maximum voltage that can be safely achieved when running an appliance.

In both the United States and Canada, the nominal voltage is 120/240, while the rated voltage is usually 125/250. However, the nominal voltage can vary up to 5 percent, plus or minus.

Moving beyond nominal and rated voltage things can get a bit more tricky.

While you may have seen the voltage markers LV (Low Voltage), MV (Medium Voltage), HV (High Voltage), or even ELV (Extra-Low Voltage) and EHV (Extra-High Voltage), the exact voltages for these ranges can vary depending on whom you ask. This is due to differences in industry standards, states, and the ratings put out by the North Electric Code (NEC) and the Institute of Electrical and Electronics Engineers (IEEE).

But don’t worry about getting confused, every appliance in your home should be properly marked with the required voltage to operate it safely!

And for most domestic usage, the National Electric Code (NEC) standards are the only ones you need to worry about. In simplest terms –

  • Low Voltage (LV) is a voltage range that carries a low risk of injury and is commonly under 100V. For example, if you were to touch a wire carrying a low voltage current with dry hands it is unlikely you would be electrocuted.
  • High Voltage (HV) on the other hand is defined as anything above 100V that can potentially cause harm.

Outside of your home and the NEC classification, numbers can get a bit murkier. However, for domestic usage, they are generally as follows:

  • Extra-Low Voltage (ELV) would be listed as anything under 50V.
  • Low Voltage (LV) is 120V and under.
  • Medium Voltage (MV) is 240V to 360V.
  • High Voltage (HV) is anything above 600V.
  • Extra High Voltage (EHV): 1000V and up.

If you’re still uncertain about the voltage ranges in your own home, or are concerned they might be off, you can always purchase a Digital Voltage Meter to test your outlets.

The Cause of Power Fluctuations

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So if the voltage ranges coming into your home are regulated, why do power fluctuations still occur?

Power surges, sags, brownouts, and blackouts are all caused when stable voltage levels are disrupted. For example, unplugging or turning off large devices like AC units or electric motors can cause power surges. These appliances draw a lot of power when in use, so stopping them can cause a sudden increase in voltage levels.

You may have also noticed that your lights have a tendency to dim or shut off throughout the day in the summer. These brownouts are caused by a steady decrease in voltage levels, usually as a result of the power company. They do this because reducing power levels during peak hours is a great way to prevent overloads to electrical grids.

In your own home, you can work to prevent this with power suppressors or conditioners, which will work to keep your voltage levels steady.

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