Grounding Metal Boxes and Outlets - Confused by Something Simple
 

Long time lurker, first time poster. I have flogged the search engines for an answer to what I thought was a simple question and come up with too many confusing answers. Here is my question -

I am installing multiple outlets on a circuit. Using brand new 12-2 romex to rewire outlets. My circuit is properly grounded (updated box at main panel with rod and brand new interior box with ground bar). In the past, I have always used plastic boxes, but in this situation, I am having to use metal boxes. When using metal boxes for duplex outlets, are you required to ground to the metal box FIRST before the outlet itself?

I have been told that if you ground to the outlet (the outlet ground screw), the entire thing is grounded when you screw the outlet into the metal box. Makes sense, but that's not the way I was taught to do it. I was taught this way:


(1) Insert incoming (powered from circuit) wire. Attach its ground wire to the metal box via ground screw AND attach it to the outlet ground.

(2) Insert outgoing (to next outlet) wire and attach its ground wire to the metal box.

(3) Repeat until you get to the last outlet.

(4) Last outlet on circuit - attach ground wire to box AND outlet.

Who is correct?

Thanks.

Help, please!

I always twist the incoming and outgoing wires together,then pigtail from there to the box and outlet.

Everyone seems to have their own method. On new work I leave the cable that feeds the power to the box extra long. I then twist all of the grounds and lock it all together with a a green wire nut leaving the long one to come through the hole in the wire nut. I wrap the ground screw to bond the box and trim what's left to the correct length, wrapping the end around the green ground lug of the device.

Thanks so much for your help. Because neither one of you picked the method someone else told me is acceptable, I am doing it the way I learned how, as it is the closest to what you do and equally safe.

The answer is none of the above.
You ground the metal box and the receptacle in each box. Not just at the first one in the circuit.
Like already said. make up all the grounds, neutrals and hots with pigtails for the receptacles. This is when you install the grounding jumper.
I know it's overkill, but it is the right way to do this. :thumbsup:

When using metal boxes with receptacles the grounding conductor must attach to the box... now we have some options on having to install a grounding jumper from the box to the receptacle or not...

250.146 (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 a self grounding receptacle shall be permitted to ground the receptacle to the box.

Basic examples (A) type installation...
http://i171.photobucket.com/albums/u...75/graphic.jpg
http://i171.photobucket.com/albums/u...receptacle.jpg

250.146 (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...

What that means is, in option (B) if you buy self grounding receptacles, you don't need a bonding jumper from the receptacle to a flush mounted box.

In option (A) If using SURFACE mounted boxes, you don't need a bonding jumper if using self grounding receptacles, OR you remove one of the washers on the 6-32 screws on non self grounding receptacles.

The incoming and outgoing grounds need to be connected to each other and the box, not by using 2 screws into the box.

Correct, all grounds entering a box must be physically spliced together.

here ya go. fun reading.

250.148 Continuity and Attachment of Equipment
Grounding Conductors to Boxes. Where circuit conductors
are spliced within a box, or terminated on equipment
within or supported by a box, any equipment grounding conductor(
s) associated with those circuit conductors shall be connected
within the box or to the box with devices suitable for
the use in accordance with 250.148(A) through (E).
Exception: The equipment grounding conductor permitted
in 250.146(D) shall not be required to be connected to the
other equipment grounding conductors or to the box.
(A) Connections. Connections and splices shall be made
in accordance with 110.14(B) except that insulation shall
not be required.
(B) Grounding Continuity. The arrangement of grounding
connections shall be such that the disconnection or the
removal of a receptacle, luminaire, or other device fed from
the box does not interfere with or interrupt the grounding
continuity.
(C) Metal Boxes. A connection shall be made between the
one or more equipment grounding conductors and a metal
box by means of a grounding screw that shall be used for
no other purpose, equipment listed for grounding, or a
listed grounding device.
(D) Nonmetallic Boxes. One or more equipment grounding
conductors brought into a nonmetallic outlet box shall
be arranged such that a connection can be made to any
fitting or device in that box requiring grounding.
(E) Solder. Connections depending solely on solder shall
not be used.

for your added pleasure.

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 flushtype
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.
FPN: Use of an isolated equipment grounding conductor
does not relieve the requirement for grounding the raceway
system and outlet box.

I realize you ground the metal box and the receptacle in EACH box. My first question was whether the method someone gave to me was correct. Here is the method - connect both the incoming and the outgoing ground to each other - attach those to the receptacle, but not the box, as the receptacle is "connected" to the box via the receptacle's screws.

Based on the responses, the answer to that question is no, that is not correct and should not be done, which is what I believed.

However, now, the latest responses have left me confused again, as it sounds like my method is not correct either. According to the newer responses, I connect the incoming and outgoing to each other and THEN connect to the box and the outlet by pigtail or by leaving the incoming wire longer. Is this correct?

To keep this real simple and code compliant, splice all your grounds together, add a bonding jumper to the box and device... And you are correct, the DEVICE cannot bond the box, but the box can bond the device if certain requirements are met.

It doesn't matter if you leave one long or use a pigtail to the box and/or the device. What matters is that the grounds are connected together and to the box and the device.

Got it. Now, reading the code makes more sense too. This site is great. Thanks so much. Now, one day, I learn why (other than the code says so) connecting the two egcs is required rather than connecting both to the box, but I leave that for another day.