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I have 2 ground wires that I can get around the ground screw on an outlet. Is it okay to do this or do I need to use a pigtail to join the wires and have only one wire attach to the ground screw?

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In all my years I have never seen a device ground screw rated for two conductors. Even clamp type ground connectors found on GFI devices are only rated for one conductor.

You will need to pigtail a single wire to the device. This can be achieved several ways. A green wire nut, a ground crimp, or a standard wire nut are examples.

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  • Use a small wire nut to pigtail the ground wires, and screw just one wire to the ground screw.
    – Craig Tullis
    Commented Nov 28, 2014 at 22:27
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    By law, all grounds must be pigtailed as Speedy describes. This is so you can remove the device without severing the ground for devices downstream.
    – Harper - Reinstate Monica
    Commented Jan 10, 2017 at 19:56
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No you can't.

You must be able to remove devices without severing ground

If two ground wires went to a device, like they do with hots on receptacles, then if you remove the receptacle (say for servicing), you cut that ground to downstream appliances. Thanks to MWBCs and the retrofit rules, it's possible that ground may serve things that are not on this breaker. You must pigtail it - always with grounds!

In fact, MWBCs have the same rule for neutrals - "pigtail it, mustn't sever neutral for downline appliances". That's because older MWBCs are on separate breakers, and that neutral could be returning current for another breaker that you didn't think to turn off. (this is why MWBCs currently require a "common maintenance shutoff" breaker).

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The reason that wiring devices have grounding connections that accept only one wire is that otherwise, if two ground wires were connected to the device, then if someone later removed that wiring device and then re-applied power without wire-nutting the grounding conductors, there would be a break in the ground path for the downstream wiring but perhaps not the hot wires.

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Most screw terminals are designed for only a single wire.

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No. Connect only one ground wire per ground screw. Wire nut all grounds together.

It has nothing to do with a terminal "rating" per say--I mean two ground wires on one ground screw are electrically connected and grounded just fine--just like with a wire nut, but rather, it's a safety issue: if you disconnect one outlet or device, that shouldn't disconnect the ground for other devices. If 2 ground wires are on one screw, disconnecting one outlet removes the other outlet's ground too. So, pigtail the 2 grounds with a wire nut and connect only one ground wire to each ground screw. Now, when you remove that one device, the grounds for other devices remain unaffected because they remain connected to the main ground via a wire nut.

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    This doesn't really add anything to the question that hasn't been covered in the other answers.
    – JACK
    Commented Nov 4, 2022 at 23:48

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