Save Your Life

By Marcus Kirkwood

1 mA (milliamps) is the threshold of current that your body can withstand before you feel anything, according to most rating systems. 5 mA is painful. 10 mA is enough to make you lose control of your muscles, thus not allowing you to let go of whatever is shocking you. If you do the math, 10 mA has the potential to kill you as you don’t have the ability to control what amount of power is passing through your body. Getting up near 100 mA affects your breathing and heart immediately, thus having the potential to result in death. Above 100 mA, you’ve got little chance of survival and will end up with burns to boot. The question becomes, how do you make sure you don’t have 10 mA pass through your body?

GFCIs. They're a simple invention that’s been saving lives since their invention in 1961. There’s little reason to get into the details of how current, voltage and resistance relate to one another, and more importantly, our bodies. All we want to teach you today is how to avoid death or injury on a construction site (or your home).

So how does a 3-way GFCI (Ground Fault Circuit Interrupter) work? Simply put, it interrupts a circuit if certain guidelines are met. Sounds simple enough, and it is, but it’s so vital, let’s learn a little more about why.

3-Way GFCI

If power is running through a regular 12/3 extension cord (3 conductions, each 12 gauge), and the cord gets cut or frayed and runs into a pool of water, that water will be charged enough to severely injure someone who comes in contact. Is the same true with a 10/3 extension cord? Absolutely. As we learned above, all it takes is 5 mA before we start to feel some serious pain.

A GFCI is in place to cut that power to whatever cord or device is running power into something that shouldn’t receive power. If an extension cord is frayed and completes a circuit into the earth using a conductor, there is a live, open circuit that will fry anything or anyone that comes in contact with it. When Charles Dalziel invented the GFCI in the 1960s, he was smart enough to design it to pop, thus cutting off power, when 5 mA disappear from a closed circuit. Almost all power is now AC and flows in both directions. This allows a GFCI to pop within nanoseconds of recognizing that power is leaking to an unwanted source before its return to the GFCI. In other words, the nanosecond power seeps into a person instead of a closed circuit (ie power tool, light etc), the GFCI triggers and saves a person’s life.

GFCIs can be hard-wired into extension cords, wall outlets, added as an extension from a previously existing power source or built into a temporary power distribution source like a power box on job sites.

To learn more about it, take a few minutes to watch this guy who loves electricity more than anyone I know: Electricity

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