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My house is ~100 years old, and I just bought it. I have an outlet that has 2 wires, what I assume are hot and neutral but no ground wire. I'm using a Klein receptacle tester. When I plug the tester into the outlet, it says that it is correct. When I pull the outlet out of the wall away from the metal box it sits in (while still wired), the tester says there is no ground. I assume that is because the screw that I use to screw the outlet receptacle to the box it sits in is metal to metal thus "grounding" the outlet. Is this incorrect? I just want to make sure I'm not misled by this tester. I thought the purpose of ground was to provide an "error" path that leads a charge back to the panel. I've been told many different things about ground, but trying to understand in regards to an outlet how ground works and what is safe for a 2 wire outlet.

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    Can you post photos of the inside of the box in question please? – ThreePhaseEel Jan 26 at 3:16
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Metal junction boxes are typically serviced by metallic conduit that is grounded in the panel. This is particularly common in older homes that have been updated to whatever the current code was when it was rewired. Homes 100 years ago didn't require grounded outlets so when they were brought up to date it was the best way to provide proper grounding. Although a receptacle will usually ground through the attachment ears to the metal box you should still attach a ground wire to the green screw on each recptacle and run it to a grounding screw on the box.
One suggestion for the future, instead of a receptacle tester, which can be squirrely at times, you should invest in a multimeter that will give you more precise information.

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This all fits with "metal box". With a metal box and the right configuration/type of receptacle (typically called "self-grounding") you don't need a ground wire to the receptacle, and if you don't use a ground wire then as soon as you pull out the receptacle from the box the tester won't see a ground.

Everything sounds good to me.

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  • this isn't good, the grounding path through the ears isn't adequate for code, instead he should add a wire from the box to the grounding screw – ratchet freak Jan 26 at 9:03
  • @ratchetfreak I've seen others claim exactly the opposite. I don't know which is true, can you provide a code reference stating that this isn't allowed (or that a wire is required no matter what)? – FreeMan Jan 26 at 13:13
  • Generally speaking (with metal boxes) , switches ground through ears, receptacles ground through ears only if designed to do so. The bottom of the line don't. The middle and top of the line do. It is quite common. We're not talking expensive - just $2 receptacles instead of $1 receptacles. – manassehkatz-Moving 2 Codidact Jan 26 at 13:26
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    Yep, self-grounding is an optional feature for outlets, but most decent ones support it. Note that the ears of the outlet's yolk have to actually be making contact with the metal box though; if they're hitting drywall you need to add a wire because the screw itself is not a reliable grounding path (even though it'll fool a tester). – Nate S. Jan 26 at 19:25
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    A switch is able to take ground via the screw head @FreeMan because a switch is unlikely to need to sink ground current. However with a receptacle, anything could be plugged into it, so the grounding needs to be better. A "self-grounding" outlet is one with an extra contact wiper to engage the screw threads and assure good grounding there. – Harper - Reinstate Monica Jan 26 at 20:27

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