Do Extension Cords Reduce Power? (Explained)

If you’ve ever wondered whether extension cords can reduce the power getting to your appliances, you’re not the only one.

And if you’re unfortunate enough to have ever used the wrong extension cord for an appliance and damaged it as a result, you’re likely keen on learning how to avoid a repeat occurrence.

And even if that’s never happened to you, surely you’d like to make sure it stays that way. So read on, and we’ll tell you all about how extension cords impact your appliances’ power needs.

Here’s How Extension Cords Affect Power:

Extension cords do not reduce power. The extension cord doesn’t have any effect on the voltage or amperage that comes out of it. Instead, the issue lies with the connection between the extension cord and its source of power. Electrical current experiences resistance as it moves, causing a loss of charge.

Black electrical extension cord on a take-up reel with four sock

Different materials have different resistances, but even a very conductive material like copper wire experiences some resistance.

The longer the distance a current has to travel, the more resistance it will experience.

Do Extension Cords Increase the Power Usage?

From the above, we can infer that the longer the extension cord, and therefore the longer the distance an electrical current has to travel, the more resistance and loss of charge it will experience.

This means that by the time the electricity reaches the appliance, it will have experienced a reduction in voltage. Just how much voltage is lost depends on the gauge (thickness) and length of the cord.

In most cases, and when the right cords are used with the right devices, the voltage lost will be minimal, and not enough to impact the use of your appliance.

At the same time, your electrical outlet will be working to supply the current needed to power your device and will output a little more current to compensate for extension cord resistance than it would if your appliance was directly plugged into the wall.

Ultimately, this means that the answer to the question is: yes, using an extension cord will draw more power than using an appliance plugged directly into a wall outlet.

However, unless your extension cord is absurdly long, or doesn’t meet the voltage requirements of your appliance, the increase in power drawn will be a tiny amount you probably don’t need to worry about.

How Much Power Do Extension Cords Draw?

There is no catch-all answer to this question because extension cords come in all different lengths and gauges, and the power drawn will also be affected by what appliance you’re using.

Generally speaking, the thicker and shorter the cord is, the less voltage it will lose, and therefore the less additional power it will have to draw from the outlet to compensate.

Note that thickness is measured in gauge, and somewhat counter-intuitively, the lower the gauge number, the thicker the cord. For example, a 12-gauge cord is thinner than a 10-gauge cord.

Your outlet will always try to supply enough power to meet your appliance’s needs, supplying additional power to compensate for voltage loss in the extension cord (and all wires in general).

Therefore, while there is no one-size-fits-all answer, we can break it down like this:

  • The longer the cord, the more power it will draw.
  • The thinner the cord (i.e. the higher the gauge number is), the more power it will draw.
  • The more power needed by the appliance plugged into the cord, the more power it will draw.

Do Extension Cords Lose Power Over Time?

Over time? No, time has nothing to do with it. Over a long distance though? Yes, absolutely, the longer the distance a current has to travel, the more voltage it will lose as it does so.

In fact, this is true of all electrical wires, not just extension cords. All physical matter resists electricity to some degree, and we call materials with high resistance “insulators,” while materials of low resistance are “conductors.”

In a typical electrical wire, the wire itself is made of metal, usually copper, which has a very low electrical resistance, letting electricity travel easily through it.

The covering wrapped around the wire, by contrast, is usually made of plastic, rubber, or any other material with a very high electrical resistance, effectively making it a barrier to keep the electricity inside the wire from getting out.

But even copper and other highly conductive metals have some electrical resistance because all physical matter does, so a small amount of charge is still lost as the current moves through a metal wire.

Over short distances, this is barely noticeable and causes a loss so infinitesimal as to be irrelevant. However, a very long extension cord can cause enough of a loss to be noticeable.

Read our blog here about can extension cords be left outside?

What About Long Extension Cords?

What about them? As we’ve covered, the longer the cord, the more voltage a current traveling through it will lose by the time it gets from your outlet to your appliance.

By extension, the longer the extension cord is, the more additional power it will need to draw from the outlet to compensate for this loss and meet your appliance’s power needs.

Check out the chart in this guide for more information on how both length and thickness (gauge) affect voltage loss and power use with extension cords.

Do Extension Cords Use Power when Nothing Is Plugged In?

You might have heard that you shouldn’t leave your phone charger plugged in when you’re not using it because it’s always drawing power, whether it’s charing your phone or not.

Knowing this, it seems a natural assumption to think that maybe the same thing occurs when you leave extension cords plugged into an outlet with nothing at the other end.

While this might seem like a sensible guess, we have good news: it doesn’t actually work this way.

The reason phone chargers and similar devices always draw power is due to the need to convert from alternating current (AC) to direct current (DC), a topic outside the scope of this article.

Extension cords perform no such conversion, simply carrying current from an outlet to an appliance, but only if there actually is an appliance plugged in on the other end.

That being said, you still shouldn’t leave an extension cord plugged in outdoors if it’s not in use.

While it won’t rack up your electrical bill, it will slowly take damage from the elements (even outdoor-rated extension cords are not indestructible) and can eventually cause a fire or electrical short.

An indoor extension cord, on the other hand, would be relatively harmless to leave plugged in when not in use, though you might want to clean it up anyway to avoid a needless tripping hazard.

Check out our blog here about can you overload an extension cord?

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