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Old 12-17-2011, 05:05 AM   #1
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Grounding Questions - Boxes, Devices, Taps, Terminations


A few questions about grounding conductors with boxes and devices.

First, some assumptions. Please correct me if I'm wrong:

First off, I know all metallic boxes must be grounded with a green 10-32 bonding screw terminating an incoming grounding source. But that's only if the circuit's physical attachment to that box is non-metallic, like an NM-B (Romex) cable, or if a metallic cable already has a grounding conductor included like in metallic cable (MC; in which case you may as well attach that ground).

But if the attachment to box is electrical metallic conduit (EMT) or armored cable (AC), or Greenfield/BX, then if THAT conduit or AC jacket is already grounded, then it is considered "raceway ground" and no additional grounding conductor is required.

---

Now... What about devices? If it were a multi-gang switch box, for example, would the yolk of each switch--provided of course that the screw-retaining plastic bits are removed first--bolted to the grounded metal box be sufficient under current 2011 NEC standards?

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Now what about devices in non-metallic boxes? Say I have five switch loops entering a five-gang box that will have switches (switch loops being where the power source is at the device being switched, not the switch itself). Must all five circuits' grounds be bonded together in that box, or may I simply terminate each individually to the five switches that get attached to that box?

If I have to bond all five of the ground conductors in that plastic box, then run five separate jumpers to each switch, that's ten conductors that need a ginormous splice. What is the best way to bond ten conductors together--especially in a crowded box? If my assumption above that devices in metallic boxes can be bonded via their yolk attachment, this gives a huge advantage to using metallic boxes over non-metallic boxes in n-gang applications where n > 2!

---

My last question. Is it okay for a conductor to NOT terminate under a device's terminal screw and instead continue on, making that connection a tap instead of a termination? I've seen this before, but only in older installations (like 1960s or older).

If this is still perfectly acceptable, what is the correct way to do it? I've seen installations where wire form a "U" under the screw, and I've also seen installations where wire wraps once around the screw. Given that the screw is tightened well enough, either tap method should seem fine but neither one will cover as much conducting surface area as a termination where the bottom of the screwhead mashes down as much wire as possible on the same plane.

If this technique IS acceptable, couldn't I just daisy-chain a ground between five switches' ground screws as I asked in the question above?

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Old 12-17-2011, 07:54 AM   #2
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Grounding Questions - Boxes, Devices, Taps, Terminations


Simply screwing the yoke to the box does not achieve an adequate ground, but you can squash a special clip (sold separately for this purpose) in between.

Choice of: (1) ground wire to switch/receptacle yoke plus clip for box, (2) ground wire to box plus clip for switch, or (3) two pigtails one for switch and one for box. I believe that for method 1 each switch needs its own ground wire.

I would daisy chain a single ground wire from one yoke to the next; the U-loop around each ground screw is an adequate ground. This method is sometimes called "rabbit ears". But individual inspectors may accept or fail this method. He is probably concerned about too sharp a bend for the wire at the beginning and end of the U which would weaken the wire. Better not to make a complete loop with the wire crossing over itself under the screw.

If you use those green wire nuts with a hole at the small end, you can have one long bare ground wire (from one Romex cable) with several of those wire nuts along its length each holding three or four bare pigtails.

If the box does not have a green bonding screw, you can fashion your own. Don't use the screw that holds the wire clamp unless the wire clamp is metal and hits the box when screwed down without squashing your cable.

Including for five switches on separate switches, and GFCI receptacles, do connect together (bond) all the grounds entering and exiting the box.

OT: Do not bond (interconnect) neutrals of (different) incoming power feeds coming from different directions or circuits. Each neutral is connected only to portions of circuits fed by the corresponding hot wire(s). Do not connect the neutral continuing from the load side of a GFCI unit to the incoming neutral connected to the line side; the load side hot is treated as a different circuit.

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Last edited by AllanJ; 12-17-2011 at 08:14 AM.
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Old 12-17-2011, 08:03 AM   #3
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Grounding Questions - Boxes, Devices, Taps, Terminations


Here is the NEC regarding grounding switches:

404.9 Provisions for General-Use Snap Switches.
(A) Faceplates. Faceplates provided for snap switches
mounted in boxes and other enclosures shall be installed so as
to completely cover the opening and, where the switch is flush
mounted, seat against the finished surface.
(B) Grounding. Snap switches, including dimmer and similar
control switches, shall be connected to an equipment
grounding conductor and shall provide a means to connect
metal faceplates to the equipment grounding conductor,
whether or not a metal faceplate is installed. Snap switches
shall be considered to be part of an effective ground-fault
current path if either of the following conditions is met:
(1) The switch is mounted with metal screws to a metal box
or metal cover that is connected to an equipment grounding
conductor or to a nonmetallic box with integral means
for connecting to an equipment grounding conductor.
(2) An equipment grounding conductor or equipment bonding
jumper is connected to an equipment grounding termination
of the snap switch.

Under the 2011 NEC switch loops now require a neutral unless the wiring is in conduit, or one side of the wall is open to allow installation of a neutral in the future.

All the grounds need to be connected together, even if from different circuits.

The NEC does not prohibit the looping of conductors and continuing to another device.
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Old 12-17-2011, 08:06 AM   #4
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Grounding Questions - Boxes, Devices, Taps, Terminations


If you use self-grounding devices or the device is installed with solid metal to metal contact between the device and the box then a grounding pigtail is not required between the device and a metallic box.
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Old 12-17-2011, 06:44 PM   #5
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Quote:
Originally Posted by Jim Port View Post
Under the 2011 NEC switch loops now require a neutral unless the wiring is in conduit, or one side of the wall is open to allow installation of a neutral in the future.

All the grounds need to be connected together, even if from different circuits.

The NEC does not prohibit the looping of conductors and continuing to another device.
Hey Jim! Yes... a neutral sitting in a switch box! I noticed this in an installation that was completed just a couple months ago, which I just modified a few weeks ago. A neutral was sitting there in the box, with a wire nut on it, doing nothing...

I modified that switch box from a single-gang three-way switch to a dual-gang having both that existing three-way and a new single-pole switch. (It was a 4-inch box so the conversion from single- to dual-gang was easy). I wired a jumper to tap off the existing three-way common to power the single-pole, then I used that extra conductor to send switched power back up to the fixture box to switch the light that was formerly switched by the three-way.

Of course I wrapped tape around the white formerly-neutral wire on each end to re-identify it as load-carrying.

The three-way switch that remains still switches the rest of the lights downstream from the fixture box I was working on.

So I suppose that's now a violation according to 2011 NEC since that neutral is missing. Probably should have fished another conductor through the conduit. But I wonder what the theory is for having a neutral sitting there, unused, in a switch box is for? Future receptacles?
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Old 12-17-2011, 07:57 PM   #6
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Grounding Questions - Boxes, Devices, Taps, Terminations


Some of the newer occupancy sensors and smart switches require a neutral. This is a change to ensure they can be installed later.

Previously, some would use the grounding conductor to provide a bootleg neutral to those type of devices.
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Old 12-17-2011, 08:03 PM   #7
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Quote:
Originally Posted by Jim Port View Post
Some of the newer occupancy sensors and smart switches require a neutral. This is a change to ensure they can be installed later.
Previously, some would use the grounding conductor to provide a bootleg neutral to those type of devices.
Ah, that makes perfect sense. I have some occupancy sensors in my house that don't require a neutral (or bootleg ground). Somehow they work, probably through induction or something magical like that.

Or, maybe they bootleg neutral internally in the switch from the ground connection. I should try disconnecting the ground to see if the switch still works.

Last edited by aaronk; 12-17-2011 at 08:08 PM. Reason: Additional thought
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Old 12-17-2011, 08:48 PM   #8
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Quote:
Originally Posted by AllanJ View Post
Don't use the screw that holds the wire clamp unless the wire clamp is metal and hits the box when screwed down without squashing your cable.
Not quite, from 250.148


(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 or a listed grounding device.

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Last edited by Jim Port; 12-17-2011 at 08:50 PM.
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Old 12-17-2011, 09:32 PM   #9
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Quote:
Originally Posted by Jim Port View Post
Not quite, from 250.148
If he's referring to those metal outlet boxes that have 3/8" knockouts with a clamp bar that is tightened down with a long 10-32 screw (to secure NM or AC/MC cables), then yes, I would not dual-purpose that screw for both clamping and ground termination because the torque required for a good electrical ground termination would be too excessive for the clamping and damage the cable (at least NM cable); and conversely, the torque for clamping could be insufficient for a good ground termination.

So, yeah, you should have a separate ground termination in the box utilizing a separate 10-32 tapped hole and ground screw. One of those extra 10-32 threaded holes exists on the other end of the box--I always remove and discard the screw/clamp apparatus on the end of the box that has no cable entering it (to increase fill capacity).

There was one really old outlet box I was working on, designed for loom-jacketed wire (knob-tube wire) that had a very similar clamp apparatus. Only the knockouts of the box were a little different than a modern box--they were round 3/8" circular holes instead of the current shape which looks sort of like a fat keyhole. I then used the 10-32 tapped hole for the green ground screw and successfully ground-bonded that old box.

It's always nice to reuse old materials when it's safe and legal to do so!
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Old 12-17-2011, 09:49 PM   #10
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Quote:
Originally Posted by AllanJ View Post
Simply screwing the yoke to the box does not achieve an adequate ground, but you can squash a special clip (sold separately for this purpose) in between.
Allan, what do these clips look like?

I've seen "spec-grade" receptacles that have a clip on one end of the yoke where the 6-32 attachment screw is suspended between two thin wires mounted in the clip. I figured this was just a fancy "spec-grade screw retainer" and had no grounding function beyond the yoke-to-box contact itself. I have NOT seen these same clips on "spec-grade" switches, though. I also am not aware you could buy these separately from the devices that come with them--at least home center big box stores don't carry them.

Perhaps you're referring to a different clip--the green ones that are designed to clip a grounding conductor to the edge of a metal box? These:


Last edited by aaronk; 12-17-2011 at 09:49 PM. Reason: Corrected misspelling
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Old 12-17-2011, 09:56 PM   #11
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Grounding Questions - Boxes, Devices, Taps, Terminations


Regarding your installation of the wire into the fixture with the screws. You can put it in as a U or totally wrap it around. It's personal preference.

That said, always install the wire into the direction it screws closed. If you screw it, it should get tighter in and close in with the fixture, and not try and open up. If the u or the swirl starts to open up as you screw it, you have it facing the wrong way.

Electricity constantly vibrates, the tighter it is, the longer it'll take to get loose, doing this, will keep them tighter for much longer. (it takes years to get loose, but hey, may as well make it last as long as you can)
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Old 12-17-2011, 10:13 PM   #12
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Quote:
Originally Posted by BigGuy01 View Post
That said, always install the wire into the direction it screws closed.
Yep... always wrap clockwise.

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