Grounded receptacles

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ammklq143

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Location
Iowa
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Electrician
What is the main purpose of the three wire 120v circuit with 3 prong grounded receptacles compared to the older 2 wire 2 prong receptacles? Human safety, lightning protection, etc.?

Thank you.
 
ammklq143 said:
What is the main purpose of the three wire 120v circuit with 3 prong grounded receptacles compared to the older 2 wire 2 prong receptacles? Human safety, lightning protection, etc.?

Thank you.
Click to expand...
Human safety.

The metal body or frame of devices plugged into the outlet would be connected to the "grounding" wire. If a fault occurred which allowed the metal body or frame to become energized, the current would flow back to "ground" and the resulting short-circuit would cause the OCPD (breaker or fuse) to trip/blow.

If not for the ground wire, the metal body or frame of the faulty device could remain energized creating an electrocution hazard.
 
190626-9842 EDT

If there was a solid short circuit in the motor from hot to the motor frame, then for most branch circuit wiring the voltage motor frame voltage would be about 1/2 the supply voltage relative to remote earth. And local earth voltage at the motor might be about equal to remote earth.

Note: the branch circuit EGC gets its connection to earth back at its main panel or thereabouts.

.
 
gar said:
190626-9842 EDT

If there was a solid short circuit in the motor from hot to the motor frame, then for most branch circuit wiring the voltage motor frame voltage would be about 1/2 the supply voltage relative to remote earth. And local earth voltage at the motor might be about equal to remote earth.

Note: the branch circuit EGC gets its connection to earth back at its main panel or thereabouts.

.
Click to expand...

Yup, and this is where the breaker comes in, killing that 60 volts to remote earth.
 
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