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From reading this article it seems like an ungrounded 3-pronged outlet can be made safe by installing a gfci downstream in the circuit.

Although the technique of installing GFCI devices in an ungrounded circuit doesn’t ground the circuit, it does provide protection in the event that any electricity leaks to ground, thereby preventing electrical shocks and injury.

So, what is the benefit of having both a GFCI (say right in the panel) and a ground in the box?

Does the ground in the box provide any extra protection or benefit beyond the protection of the GFCI?

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Protection, in theory, no. The GFCI takes care of the “killing” risk of an outlet, at least, it does as well as grounding does.

However actual grounding does something GFCI does not: provides a place for natural electricity to go, notably ESD from shuffling your feet across the carpet in winter. With a ground wire, that simply goes into the building’s grounding electrode system.

Without a ground wire, it finds a place the equipment is not insulated for 20,000 volts (many such places), and leaps to the hot or neutral wire, then goes through equipment if necessary to the neutral wire, then via the house’s neutral-ground equipotential bond to grounding electrode. The equipment might not enjoy this too much.

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  • So without a ground it could still be dangerous for equipment, but it couldn't harm a person? – Jordan Jul 15 '20 at 12:08
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    A properly installed GFCI should prevent human harm, unless the human is doing something fairly stupid. – Harper - Reinstate Monica Jul 15 '20 at 13:45
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I think it really depends on the value of your grounding electrode, your grounding electrode system connects to earth and provides a path for ground faults and this path is supposed to assist in the fault clearing or tripping the breaker.

The problem is what happens if your body is in the fault path the breaker won’t trip until you are long gone, introduce the GFCI they measure the hot and neutral when there is an imbalance or a fault above 5 ma they interrupt the current so you will still be here having just received a little jolt Or shock.

A grounded system is best as it takes the protection of the ground to each device. the GFCI circuitry only uses hot and neutral so the ground is an additional protection With some metallic hand tools the ground prevents you from getting in the path of a fault.

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  • So what is the danger for a human with a GFCI protected but ungrounded outlet? I'm not sure what "your body is in the fault path" means? Can you provide an example? – Jordan Jul 15 '20 at 14:42
  • Really there is not much danger, 5ma is below the level that will freeze your muscles, but would I stand in a pool of water and dunk a live cord that is GFCI protected ? Heck no. As far as your body being the fault path getting a shock “hand to hand” creating a path from a wire or electrical source through your chest and ground with your other hand is the most dangerous path as the current affects your heart (your heart works with very tiny electrical impulses). I have been shocked more than a time or two and the few times I was on a protected circuit I was glad it was there water involved. – Ed Beal Jul 15 '20 at 16:01

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