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Wiring outlet box

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Posted on April 14, 2017 at 10:44:13
JB Coleman
Audiophile

Posts: 158
Location: Michigan
Joined: January 3, 2007
 A (hopefully) quick question:

I own an old house with original plaster walls, and want a dedicated outlet installed in my music room. I'm told the most efficient way to do this is to run romex through the floor, into an aluminum outlet box (on which I'll be placing my Oyaide WPC-Z plate) screwed into the floor. The electrician doesn't think that the outlet box itself needs to be grounded. So here's my question: is he right? Is there any advantage to grounding the outlet's aluminum box, or is it okay for audio purposes to leave it ungrounded? Thanks in advance,

JB Coleman

 

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RE: Wiring outlet box, posted on April 14, 2017 at 12:32:16
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
 Your electrician is wrong. If a metal box is used it must grounded. Why doesn't he, or you, not want to ground the box?

 

RE: Wiring outlet box, posted on April 14, 2017 at 15:57:42
JB Coleman
Audiophile

Posts: 158
Location: Michigan
Joined: January 3, 2007
 No clue, which is why I decided that post about it here. You've confirmed my suspicions, in any case. Thanks,

JB Coleman

 

RE: Wiring outlet box, posted on April 14, 2017 at 16:57:40
Uncle Mike



The ground would be attached to the ground strap on the receptacle which in turn is mechanically fastened to the outlet box. Therefore the box is grounded.

 

RE: Wiring outlet box, posted on April 14, 2017 at 18:54:08
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
 In your examples the boxes are fed with metallic conduit. The metallic conduit is the equipment grounding conductor. The box is bonded, connected, to the equipment grounding conductor by the conduit box connector.

Also notice the boxes are surfaced mounted.If the box is flush mounted a grounding jumper is required from the ground terminal on the receptacle to the box. Exception: If the receptacle is an approved auto grounding type
receptacle the grounding jumper is not required.

Say the box is a steel 4"X4" surface mounted box and a steel 4"x4" raised duplex cover will be used to support the duplex receptacle. Even though the steel raised cover will be fastened to the box by the two 8/32 supporting screws NEC code requires a bonding ground jumper wire to be installed from the ground terminal on the duplex receptacle to the 4"x4" steel box. Why? Because if the raised cover is removed from the box and the jumper is not installed there is the risk the cover could become energized and create a shock hazard to the person who removed the raised cover. Yes the person should have turned off the circuit first. NEC tries to make the code as idiot proof as possible.

1900 raised duplex cover
http://www.garvinindustries.com/images/itemimages/g1938.jpg


As for the OP's situation. IF Romex is used to feed the new floor flush mounted aluminum box the electrician could have simply stripped the outer jacket longer than needed then half curled the bare ground wire around a 10/32 green ground screw in the back of the box and fastened the remaining end of the bare ground wire to the ground terminal of the duplex receptacle.

The electrician could have also pig-tailed two ground wires to the Romex bare ground wire and connected one to the box and the other to the ground terminal on the duplex receptacle.

Why not just connect the bare ground wire from the Romex to the duplex receptacle ground screw and then let the yoke, supporting back strap, bond the equipment ground to the box that way? Because NEC code says that does not meet code. Why? What if someone pulls the receptacle from the box? The metal box is no longer grounded. It is no longer idiot proof.

Note: If the aluminum box does not have a tapped 10/32 hole in the back of the box and the electrician does not want to take the time to drill and tap the hole or drill a hole and fasten a ground pigtail with a machine screw and nut he could have simply used a green drive on wire ground clip on the side of the box and fastened a ground jumper pigtail wire there.

http://www.homedepot.com/catalog/productImages/1000/e1/e144b5ab-fc7b-4530-a3b2-b6d5944a2da9_1000.jpg


Note: Even if the aluminum box will be surfaced mounted to the floor the box still must be bonded directly to the bare equipment grounding conductor of the Romex. That is if the OP wants to meet bare minimum NEC safety electrical standards.

 

RE: Wiring outlet box, posted on April 15, 2017 at 03:40:36
Uncle Mike
 If you take note the picture references NEC code. While it does show a metal conduit, in housing it is only required where the cable would otherwise be exposed, I.E. up a wall into the joists (again NEC code and BOCA), therefore no promise that it is grounded. I'm aware the picture does not show the ground wire connected but if the insulating tabs are removed with the ground wire connected to the box or the receptacle (I prefer the receptacle)both are considered grounded.
Perhaps that is why the OP's electrician wasn't concerned about grounding the box.

 

RE: Wiring outlet box, posted on April 15, 2017 at 05:17:16
Kingshead
Audiophile

Posts: 574
Location: Florida
Joined: September 14, 2016
 Licensed master electrician since 1986, the box needs to be grounded. Even when using grounding type receptacles it's still a good idea. As for the conduit being the ground for the box, that's only acceptable if certain criteria are met, such as all connectors and couplings shall be of the set screw type, if FMC (flexible metal conduit) (or greenfield as its often called) it must have the integral copper bond wire and can't be run more than 6' in length. If the knock outs are concentric all must be removed or even the set screw connector isn't considered a sufficient bond.

In the pictures above the one to the right would still need the box bonded by the ground wire, the conduit is connected with a compression connector, this is not considered a good enough bond.

In any event, there's absolutely no reason not to bond the box other than laziness.

Martn

 

RE: Wiring outlet box, posted on April 15, 2017 at 05:23:20
bcowen
Audiophile

Posts: 1076
Location: North Carolina
Joined: December 19, 2015
 Why not just use a plastic j-box, and all the grounding issues go away? :)

 

RE: Wiring outlet box, posted on April 15, 2017 at 05:28:09
Kingshead
Audiophile

Posts: 574
Location: Florida
Joined: September 14, 2016
 Plastic boxes are great, use them all the time, but there are some instances where it's just not feasible. Without seeing the installation it can only be surmised the electrician used a metal box for a reason.

Martin

 

RE: Wiring outlet box, posted on April 15, 2017 at 05:33:14
Kingshead
Audiophile

Posts: 574
Location: Florida
Joined: September 14, 2016
 Yes it does reference the code, but it's wrong. The far right box in the picture is connected with a compression connector, this is not considered an acceptable bond by the NEC, it must be a set screw type connector as shown for the other boxes.

Martin

 

RE: Wiring outlet box, posted on April 15, 2017 at 07:20:56
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
 If you take note the picture references NEC code.

Yes it does, Article 250.146 Connecting Receptacle Grounding Terminal to Box.

And for the pictures shown in your link 250.146(A) Surface Mounted Box.

You are looking at the wrong section of Article 250 though. You need to read 250.148 Continuity and Attachment Of Equipment Grounding Conductors to Boxes.

 

RE: Wiring outlet box, posted on April 15, 2017 at 07:24:33
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
 The far right box in the picture is connected with a compression connector, this is not considered an acceptable bond by the NEC, it must be a set screw type connector as shown for the other boxes.


Wrong.

 

RE: Wiring outlet box, posted on April 15, 2017 at 08:07:29
Kingshead
Audiophile

Posts: 574
Location: Florida
Joined: September 14, 2016
 I've been doing this for almost four decades, apparently they've amended the code to allow compression connectors UL listed or approved for the purpose and provide an adequate path for ground. This is rather open ended as it leads to all kinds of problems if not adequately employed. First, there's a maximum length the conduit can be run without a ground installed with variables such as number and size of conductors installed, voltage, amperage, type of conduit etc. If someone is injured or killed and the installation is found inadequately grounded through testing it wouldn't be pretty.

Just as its perfectly fine to use the device (meaning the receptacle) as a means of circuit continuity, IE back stabbing or wrapping the screws, but any electrician worth his salt would tail the wire's first, and not use a compression connector as part of the equipment ground integrity.

Martin

 

RE: Wiring outlet box, posted on April 15, 2017 at 08:30:12
JB Coleman
Audiophile

Posts: 158
Location: Michigan
Joined: January 3, 2007
 Thanks to everyone for the feedback. I've run a ground jumper to the box.

A related question: I've now got both tabs of the outlet's ground strap to the box, as well as the ground jumper. Is there any concern about having too many connections to ground? Perhaps isolating one of the two tabs of the ground strap from the box would be advisable?

JB Coleman

 

RE: Wiring outlet box, posted on April 15, 2017 at 09:52:42
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
 A related question: I've now got both tabs of the outlet's ground strap to the box, as well as the ground jumper. Is there any concern about having too many connections to ground? Perhaps isolating one of the two tabs of the ground strap from the box would be advisable?

As it pertains to NEC code, no. Everything meets bare minimum NEC electrical safety standards. (I assume the electrician bonded the bare equipment grounding conductor of the Romex to the aluminum box so as to meet NEC.)
The Purpose of the NEC code is for the protection of life and property. NEC could care less how your audio system sounds. NEC is not meant to be used as a how to instruction manual.

.

 

My thought exactly. [nt], posted on April 15, 2017 at 11:36:16
alan m. kafton
Manufacturer

Posts: 5285
Joined: April 7, 2000
 .

 

RE: Wiring outlet box, posted on April 16, 2017 at 09:19:12
Duster
Manufacturer

Posts: 17117
Location: Pacific Northwest
Joined: August 25, 2002






The state of the art Oyaide WPC-Z milled aluminum mounting bracket with carbon fiber faceplate depends on a very rigid coupling of the massive aluminum bracket via both mounting screws to an AC outlet box, and for both ears of the AC outlet ground strap to be rigidly affixed to the aluminum bracket with four screws, two screws for each ear. I would not try to insulate one of the ground strap ears, nor try to insulate one of the u-shaped slots of the aluminum bracket in search of better audio performance. I would have to read a credible report about the exact sonic betterment that such a method might provide before I attempted to experiment for myself. Perhaps Al's audio system was so far superior to mine, that even the most subtle differences were clearly audible to his ear, but that's just my 2 cents worth. YMMV

 

RE: Wiring outlet box, posted on April 16, 2017 at 12:22:53
jea48
Audiophile

Posts: 6770
Joined: January 5, 2005
 nt.

 

RE: Wiring outlet box, posted on April 16, 2017 at 13:19:14
Duster
Manufacturer

Posts: 17117
Location: Pacific Northwest
Joined: August 25, 2002
 "I am pretty sure Al was not using the WPC-Z plate. Just a guess he was using a standard non metallic duplex cover plate."

I know Al did not use the WPC-Z, since he came late to experience the benefits of an Oyaide AC outlet. He replaced a special Pass & Seymour with an Oyaide SWO-GX and liked it very much.

"Looking at the WPC-Z plate mounting it would still be possible to try Al's experiment. For the test an insulator would be placed between the back side of the WPC-Z plate and the metal wall outlet box. A nylon 6/32 screw would be installed on the opposite end of the duplex equipment ground screw of the WPC-Z plate to support that end of the WPC-Z plate to the wall outlet box. I believe that would still break one end of the one pole inductor that AL spoke of in his post/s."

What kind of insulator might you have in mind? Before I would place a compliant insulation layer, which would partially decouple the structure (not something I want to do), I wouldn't want anything to get in the way of the most rigid interface structure as possible. The use of a nylon screw kills the whole recipe for me.

 

RE: Wiring outlet box, posted on April 16, 2017 at 17:02:08
JB Coleman
Audiophile

Posts: 158
Location: Michigan
Joined: January 3, 2007
 Thanks for the detailed response with respect to the WPC-Z. I've been using mine for several years, and I'm not keen to alter it. I'm leaving it uninsulated.

JB Coleman

 

RE: Wiring outlet box, posted on April 18, 2017 at 11:20:50
alan m. kafton
Manufacturer

Posts: 5285
Joined: April 7, 2000
 Please explain "tail the wires first"....thanks in advance.

 

RE: Wiring outlet box, posted on April 18, 2017 at 15:55:42
Kingshead
Audiophile

Posts: 574
Location: Florida
Joined: September 14, 2016
 Well its much easier with pictures, I actually posted a tutorial on AK about this very subject.

It's not that hard to do, but it adds time, and materials to the job, so many electricians don't do it because it's not required by the NEC, but it should be. It's my opinion arc fault breakers would never have come into existence if electricians had only been required to do this.

I'll try to explain. If you were to remove the receptacle from the box and looked inside you would see at least one black, white, and bare (maybe green) wires.

When there are two or more of each the bare wires are twisted together with one tail going to the outlet's ground screw. Then the blacks and whites are either back stabbed into the holes, or wrapped around the screws on the receptacle. This makes the device an integral part of the circuits integrity. If the first receptacle in line it takes all of the abuse of the whole circuit even if never used.

What should be done is the same as with the ground wires. Take a 6" - 8" piece of black wire, with a wire nut tail it to the two black wires in the box, do the same with the white wires. Now connect the other end of the tails to the receptacle, the power can now flow on the wires past the receptacle, and any others in the line also tailed in this manner to its desired location. Now the receptacles throughout the house will only be in use when something is plugged into each if them, and it will only carry its own load.

Hope I was able to make this clear, will see if I can still find the pictures I took when I posted this on the other site.

Martin

 

RE: Wiring outlet box, posted on April 18, 2017 at 16:17:54
Kingshead
Audiophile

Posts: 574
Location: Florida
Joined: September 14, 2016
 Found the pics, apologize for thread jacking.




Things you will need.




What you will typically see.




Wires removed from receptacle, tailed, then reconnected using the two tails.



Wire nuts installed, ready to put back in use.


Martin

 

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