The longer answer is also no.
You don't need a seperate ground, ONLY when the receptacle's tab is in full contact with the metal box.
...I have to add, in all fairness, that I see this rule broken a lot more often than I see it observed. I always thought the mounting screws served as ground, too, until Mike told me otherwise.
And it still doesn't make that much sense to me, the cross-section of those two screws must be pretty damn close, if not over, the cross-section of a 12-gauge wire? But I don't write or interpret the rules...
Sorry not to have warned you, Ian, I thought you were on plastic boxes.
... had to look it up.
12-gauge wire is 0.0808" diameter, 6-32 screw's shaft is 0.0997". Steel instead of copper, but there's 2 of them... Weird / silly rule, then, I think. Wish Mike or Pete was around to explain the rationale, but neither's been around, lately.
Thanks for the info - would not have known about the need for pigtails if using a plastic box extender between receptacle and box.
I always do that regardless to ensure the receptacle/metal box remains grounded if the receptacle is removed (or comes loose) from the metal box.Quote:
Oops - plastic extenders on metal boxes?
Means now you need to pigtail a ground connection between the receptacle and the metal box.
In fact, I thought it was code.
Oh, I've just realised what you mean. A grounded box can ground the receptacle, but a grounded receptacle cannot ground the box. And a plastic extender messes up the former.
Nevertheless, I am still OK due to my craftmanship!
I've always run a ground to the metal box too
Never relied on just the screws, some of them are real rusty
No, Ian, I meant what you said the first time. You box is grounded, regardless.
In walls or ceilings with a surface of concrete, tile, gypsum, plaster, or other noncombustible material, boxes employing a flush-type cover or faceplate shall be installed so that the front edge of the box, plaster ring, extension ring, or listed extender will not be set back of the finished surface more than 6 mm (¼ in.).
In walls and ceilings constructed of wood or other combustible surface material, boxes, plaster rings, extension rings, or listed extenders shall be flush with the finished surface or project there from.
406.4 Receptacle Mounting.
Receptacles shall be mounted in boxes or assemblies designed for the purpose, and such boxes or assemblies shall be securely fastened in place unless otherwise permitted elsewhere in this Code.
(A) Boxes That Are Set Back. Receptacles mounted in boxes that are set back from the finished surface as permitted in 314.20 shall be installed such that the mounting yoke or strap of the receptacle is held rigidly at the finished surface.
406.10 Connecting Receptacle Grounding Terminal to Box.
The connection of the receptacle grounding terminal shall comply with 250.146.
250.146 Connecting Receptacle Grounding Terminal to Box.
An equipment bonding jumper shall be used to connect the grounding terminal of a grounding-type receptacle to a grounded box unless grounded as in 250.146(A) through (D). The equipment bonding jumper shall be sized in accordance with Table 250.122 based on the rating of the overcurrent device protecting the circuit conductors.
(A) Surface-Mounted Box. Where the box is mounted on the surface, direct metal-to-metal contact between the device yoke and the box or a contact yoke or device that complies with 250.146(B) shall be permitted to ground the receptacle to the box. At least one of the insulating washers shall be removed from receptacles that do not have a contact yoke or device that complies with 250.146(B) to ensure direct metal-to-metal contact. This provision shall not apply to cover-mounted receptacles unless the box and cover combination are listed as providing satisfactory ground continuity between the box and the receptacle. A listed exposed work cover shall be permitted to be the grounding and bonding means when (1) the device is attached to the cover with at least two fasteners that are permanent (such as a rivet) or have a thread locking or screw locking means and (2) when the cover mounting holes are located on a flat non-raised portion of the cover.
(B) Contact Devices or Yokes. Contact devices or yokes designed and listed as self-grounding shall be permitted in conjunction with the supporting screws to establish the grounding circuit between the device yoke and flush-type boxes.
(C) Floor Boxes. Floor boxes designed for and listed as providing satisfactory ground continuity between the box and the device shall be permitted.
(D) Isolated Receptacles. Where installed for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, a receptacle in which the grounding terminal is purposely insulated from the receptacle mounting means shall be permitted. The receptacle grounding terminal shall be connected to an insulated equipment grounding conductor run with the circuit conductors. This equipment grounding conductor shall be permitted to pass through one or more panelboards without a connection to the panelboard grounding terminal bar as permitted in 408.40, Exception, so as to terminate within the same building or structure directly at an equipment grounding conductor terminal of the applicable derived system or service. Where installed in accordance with the provisions of this section, this equipment grounding conductor shall also be permitted to pass through boxes, wireways, or other enclosures without being connected to such enclosures.
Pretty simple, the box must be extended to comply, either flush or no more than one quarter inch back on a noncombustible wall.
The equipment grounding conductor must land on the device simply because direct contact to the original box can not be achieved as the receptacle must sit firmly against finished wall.