Thanks to Stackexchange's Hot Network Questions, I found out that my 3-prong dryer outlet was a safety hazard and I'm replacing it with a 4-conductor 14-30R receptacle and matching cord. I've replaced the dryer cord and now I'm working on the receptacle. The circuit feeding the dryer has a 4-wire cable, with the ground wire screwed to the old 3-prong surface-mount receptacle.
I had been thinking that in addition to connecting the ground wire to the new receptacle, I would also need to run a ground wire from the ground terminal on the new receptacle to a ground screw in the metal box I'm mounting the receptacle in. However, the new receptacle seems to have a built-in solution to this problem: the ground terminal has a metal strap connecting it to the mounting plate. So it seems to me that once the receptacle is screwed into the box cover, and the box cover to the box, the box is grounded and therefore I don't need a separate ground wire. Is that correct?
A few other details:
- The new receptacle is a Utilitech 2105S.
- I am planning to mount it in a RACO #8232 4-inch steel box, surface-mounted on a concrete wall, using a RACO #810C steel box cover.
Here's the metal strap connecting the ground terminal to the outlet's built-in mounting plate, which in turn is screwed into the box cover:
Best Answer
Anytime you have a metal box, you ground the metal box FIRST.
When the receptacle's yoke has hard-flush metal-metal contact with the junction box cover, and the cover has hard-flush bare metal-metal contact with the junction box, then it picks up grounding that way. There are other ways as well.
However, you NEVER connect the ground wire to the receptacle and fail to ground the metal box. In that case, the box's grounding will fail if you remove the receptacle.
"Grond the metal box first" works well for pushing the ground wires out of the way into the very bottom of the box. When using one of the allowed methods of grounding a recep via the box, it means you don't have to handle ground wires at all when trying to assemble the box. One less wire to wrestle!