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Name: Amy
Status: Other
Grade: Other
Location: WV
Country: United States
Date: November 2007


Question:
Can electric current run through an extension cord or a charger cord if it is plugged into a wall but nothing on the other end? for example, if I leave my cell phone charger plugged in but the phone is not attached.



Replies:
Hi Amy

Good question. Even though your phone isn't plugged into the charger, the charger is still there and it will still draw some current. It will be much less than if it is charging your phone, but it will still draw some current. Interestingly enough, even if you do not have anything plugged into any outlet and all your lights and appliances are turned off, if you measure the current going into your house you will find that a very small amount of current still flows. This is called leakage current and happens because the insulation used in distributing the power is not perfect. To keep things green, you want to unplug things like chargers if you are not using them. Hope this helps.

Bob Froehlich


Hi Amy,

No; electric current cannot flow into a wire that has nothing at the other end. In your example, though, please note that the cell phone charger itself will use a small amount of energy even though no phone is plugged into it. You can feel that the charger gets slightly warm when left plugged in even though the phone is not connected to it. This is because the electrical transformer inside uses a little energy even though no electrical current is flowing into the cable.

Regards,

Bob Wilson.


Yes. In the case you give, the charger is running a current (though it is likely small) because the charger is still converting the wall voltage to the voltage for your cell phone... even though the phone is not attached. If it were only an extension cord - just two wires running to an extension outlet - no current would run. Those are two different situations.

Larry Krengel


The answer is: basically no, if nothing at all is plugged into the extension cord then there is no current. Most chargers draw a small amount of current, even when the phone is not plugged in, and in this case, yes, a small current flows. That causes idle or parasitic power to be consumed. If the power supply feels warm, then it is drawing current and consuming power.

There are hundreds of millions of chargers in the US, and even if the current draw is small, it adds up to significant power. You may have noticed that very modern chargers are cleverly designed to draw negligible current when plugged in. They do not feel warm at all.

Robert Erck



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