Two Prong Plug to Three Prong Extension Cord?

I recently purchased a new portable electric Kobalt "inflator" (i.e., air compressor). Its power cord for 120-volt household current has a 2-prong plug with one prong thicker than the other, as is common/required nowadays. However, in order to use this inflator in our parking garage, I have to use a 25-foot, 12-gauge outdoor extension cord, even though I will be using the inflator indoors in the garage.


The extension cord has a 3-prong plug and fits correctly into the 3-point electrical outlets throughout our 8-year-old building. The "female" receptacle at the other end of the extension cord is also 3-point. My question is can I plug the 2-prong plug of the new inflator into the 3-prong receptacle of my extension cord, leaving the 3rd/bottom hole empty? There doesn't appear to be any other choice.

By David N.

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March 27, 20151 found this helpful
Best Answer

If the compressor came as a two wire unit (not a three with the ground pin cut off) then yes you are good to go.
You should verfiy your garage is GFCI protected as is required by code.

The purpose of the ground pin is to ground the metal parts of the case of what you plug into it. If your compressor is plastic, there is no metal to ground.


Why would you want to ground the metal case? If the hot wire inside your device touches the metal case and you touch it, you get shocked or electrocuted. If the case is grounded and the hot wire touches it, the breaker trips.

Many tools are double insulated (shown as a square within a square). These tools require no ground pin.

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May 25, 20200 found this helpful
Best Answer

The way electricity works , if the metal case is touching the hot wire and it's grounded, it now has a really easy path to ground, so it will not want to travel through your body. This will also cause a spike in current and trip your breaker right away. If the metal case is ungrounded, the case will be sitting at that "hot" voltage waiting for you to touch it so it can travel to ground through your body.


If you have a GFCI outlet is nice because you don't need the 3rd prong (ground), its able to detect if the hot wire touches anything it isn't supposed to.

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June 22, 20170 found this helpful

hello. I came across this thread after having purchased the exact same device. It is an automobile tire inflator branded Kobalt and sold at Lowes. The documentation makes it sound as though the device would be damaged if you plug it's two prong polarized cord into a three prong extension cord. Can anyone out there with knowledge of electrical devices verify that device is unlikely to become damaged, safety issues aside.
Many thanks!
Ps. this is a cool little unit. Runs off both 120 V AC and 12 V car auto battery. never put quarters into that gas station air pump thing again!

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October 12, 20170 found this helpful

Yep, is the short answer.. (and the long answer too). Yes, yes and yes.

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