Metal conduit. Are grounding screws needed?

[RickDel]

Hey guys....I'm making progress on my subpanel install and want to know if my metal boxes need grounding screws.

I'm running two 50amps and one 20amp circuit off my 100amp subpanel in the garage.

I plan to just run two grounding conductors through the one run off the right so no splices.

Do I need to use grounding screws in my boxes and pigtail the receptacles, or just ground the receptacles?

Thanks - Rick

 

[Norcal]

The 50A receptacle will need a jumper from the box to the device, if a grounding conductor is pulled it will need to be bonded to the box, some 15A & 20A receptacles are listed as "self-grounding" they do not require a jumper, if not they will.

 

[RickDel]

Thanks Norcal

So, if I need a jumper from the box the receptacle, can I just use one of the screws I used to mount the box? (I think I may have used the grounding screw hole to mount the box) Or should I drill a small hole and install a green ground screw?

Also, do I run the ground conductor to the box and then pigtail to the box and the receptacle?

Thanks

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[wyliesdiesels]

The conduit counts as an EGC so you could just forgo the green EGC conductor in the pipe and bond the non "self-grounding" outlets to the box with a green screw. No u cant use any screw. Need to use the green screws supplied with the box...

What size wire are you using for the 50a outlet?

Whats the 50a outlet for?

 

[RickDel]

Thanks wyliesdiesels

I read some differences of opinion on using an EGC with metal conduit, but thought it would be safer to just use them. I already have the THHN, and it's not a long run, so I don't mind running it.

No u cant use any screw. Need to use the green screws supplied with the box...

My boxes didn't come with grounding screws. I pulled one of the screws out I used to mount the box and installed a green grounding screw, but it's looks like it might interfere with the receptacles (not enough room). Maybe I should use grounding clips.

What size wire are you using for the 50a outlet?

I'm using 8-Gauge Stranded THHN Wire

Whats the 50a outlet for?

There are two 50's. One is for a 5hp air compressor and other is for 45amp (max) plasma cutter.

Thanks

 

[wyliesdiesels]

Thanks wyliesdiesels

I read some differences of opinion on using an EGC with metal conduit, but thought it would be safer to just use them. I already have the THHN, and it's not a long run, so I don't mind running it.

EMT has more surface area so IMHO its better than a conductor.

U will need #12 for the 20a and #10 for the 50a..

My boxes didn't come with grounding screws. There were four aligned holes in the back. One was smaller then the others, but not raised like other grounding screw holes I've seen, so I didn't think about it when I used that smaller flat hole to mount the boxes.

I wonder if I can just drill a small hole and then use a self taping green ground screw in the box. (I probably enlarged the small hole when I used it to mount the box).

I didnt phrase that right.

I shouldve said use the ones that came with the box or buy some.

If the box has a spot listed for the ground screw then you need to use that spot.

There are two 50's. One is for a 5hp air compressor and other is for 45amp (max) plasma cutter.

If the compressor's true rating is 5HP then it needs to be hardwired unless the outlet youre using is rated for 5HP or more. NEMA outlets are typically rated for around 3HP...

What is the FLA on the nameplate? Most manu. overrate and exaggerate their motor's HP ratings...

BTW a true 5HP motor only needs #10 THWN in pipe or #8/2 NM-b...

 

[pattenp]

You should not be using a plug and outlet connection for a 5HP compressor if the motor is actually listed as a 5HP on the motor data plate.

Edit: sorry to be a parrot. wylie beat my slow typing.

 

[RickDel]

Thanks wyliesdiesels

I actually edited my previous post at the same time you responded. I'll use a green grounding screw.

Thanks

 

[CJ7VFR]

...No u cant use any screw. Need to use the green screws supplied with the box...?

What about boxes, like metal J-boxes, or any other metal box, that didn't come with a green colored screw for grounding the metal box? Can you use a similar size/length screw as long as it fits correctly and the thread size is the same?

I get it that a green colored screw would indicate to anyone that the wire under it should be a ground wire. But is there actually something in the NEC codes that says you have to use a green colored screw?

I am curious about this, as I have used different screws in my metal J-boxes when they didn't come with a green colored screw. I made sure the head size was the same and thread size was the same as the green colored screws so that the wire contact area under the screw head would be the same.

Jim

 

[RickDel]

I'm not doubting your advice on hardwiring the air compressor, but can you explain the risks?

I did exactly like this guy did, except I used #8 wire (I think the compressor drawls 27 amps).

Thanks

 

[RickDel]

CJ7VFR, I found this at another site:

Depends on where it's being installed.

250.8 Connection of Grounding and Bonding Equipment.
(A) Permitted Methods. Grounding conductors and bonding jumpers shall be connected by one of the following
means:
(1) Listed pressure connectors
(2) Terminal bars
(3) Pressure connectors listed as grounding and bonding equipment
(4) Exothermic welding process
(5) Machine screw-type fasteners that engage not less than two threads or are secured with a nut
(6) Thread-forming machine screws that engage not less
than two threads in the enclosure
(7) Connections that are part of a listed assembly
(8) Other listed means


250.126 Identification of Wiring Device Terminals. The terminal for the connection of the equipment grounding conductor shall be identified by one of the following:
(1) A green, not readily removable terminal screw with a hexagonal head.
(2) green, hexagonal not readily removable terminal nut.
(3) A green pressure wire connector. If the terminal for the grounding conductor is not visible, the conductor entrance hole shall be marked with the word green or ground, the letters G or GR, a grounding symbol, or otherwise indentified by a distinctive green color. If the terminal for the equipment grounding conductor is readily removable, the area adjacent to the terminal shall be similarly marked.

406.9 Grounding-Type Receptacles, Adapters, Cord Connectors, and Attachment Plugs.
(B) Grounding-Pole Identification. Grounding-type receptacles, adapters, cord connections, and attachment plugs shall have a means for connection of an equipment grounding conductor to the grounding pole.
A terminal for connection to the grounding pole shall be designated by one of the following:
(1) A green-colored hexagonal-headed or -shaped terminal screw or nut, not readily removable.
(2) A green-colored pressure wire connector body (a wire barrel).
(3) A similar green-colored connection device, in the case of adapters. The grounding terminal of a grounding adapter shall be a green-colored rigid ear, lug, or similar device. The equipment grounding connection shall be so designed that it cannot make contact with current-carrying parts of the receptacle, adapter, or attachment plug. The adapter shall be polarized.

 

[pattenp]

The risk is if pulling the plug while under load can create an arc and burn your hand or worst throw sparks in your eyes. To be NEC compliant you need to use a plug/outlet rated for the HP of the motor. A 50A NEMA outlet/plug is rated at best for 3.5HP.

 

[RickDel]

the risk is if pulling the plug while under load can create an arc and burn your hand or worst throw sparks in your eyes. To be nec compliant you need to use a plug/outlet rated for the hp of the motor. A 50a nema outlet/plug is rated at best for 3.5hp.

thank you!

 

[CJ7VFR]

CJ7VFR, I found this at another site:

Depends on where it's being installed.

.........

Thanks for the info. It seems like they want the screw not only to be green, but to have a hex head as well.

In the cases where it did not specify the grounding screw to be green, nor have a hex head, it appears a screw of the same size and thread pitch can be used as long as it is held in place by at least 2 to 3 threads.

I see that places like Home Depot actually sell packs of the green grounding screws. I will go and pick up a pack just so I have them. Better to be safe than sorry!

Jim

 

[dscheidt]

Thanks for the info. It seems like they want the screw not only to be green, but to have a hex head as well.

Green hex head screws are readily available, and handy, but not required for boxes.

250.126 covers devices (switches, receptacles, encabulators). The screw attaching the grounding conductor to the box doesn't have to be green or UL listed (there is no listing for it to be listed under). It just needs to meet the mechanical specifications; since a box is 1/16" thick (listing minimum requirement), that means a 32 tpi screw is required to engage two threads, and tapped holes on boxes are 10-32.

 

[thewatusi]

Curious why you didn't run straight pieces of conduit horizontally between your boxes. The up and down looks sloppy imo

 

[RickDel]

Curious why you didn't run straight pieces of conduit horizontally between your boxes. The up and down looks sloppy imo

Not sure if you're trying to be a ****, but that's the only way I saw to do it. I wanted my receptacles the same height as my others and I'm not sure I could get the bends with the offset from the panel without some drop. Unless you mean horizon from the panel, in which case I didn't want my receptacles 6' off the floor. Either way, I've never done it before and I'm satisfied with it.... IMO

 

[Norcal]

Curious why you didn't run straight pieces of conduit horizontally between your boxes. The up and down looks sloppy imo

Not sure if you're trying to be a ****, but that's the only way I saw to do it. I wanted my receptacles the same height as my others and I'm not sure I could get the bends with the offset from the panel without some drop. Unless you mean horizon from the panel, in which case I didn't want my receptacles 6' off the floor. Either way, I've never done it before and I'm satisfied with it.... IMO

It could have been done differently but it's not sloppy, I would have gone horizontal, bent a 90 & a little kick to get it in the bottom of the panel, would saved some fittings & some EMT, there is nothing wrong with it, just a different way of going about it, time to pull some wire.

 

[RickDel]

Thanks Norcal. I may have got a little touchy on the "sloppy" comment. I've never bend conduit and wouldn't say it was "hard" but definitely NOT easy either. Now I'm thinking I probably should have done it differently... haha

On a separate note, I now have a problem with my ground screw location. It's interfering with the receptacle. I'm trying to fine NEC on whether I can relocate the ground screw hole by drilling and tapping a 10-32.

 

[Norcal]

You need a deeper box.

 

[RickDel]

You need a deeper box.

I was afraid of that... I just hope I can get them with the same offset or I may be rerunning conduit.

 

[brewchief]

I only buy the deep 4x4 boxes, offset to the knockouts should be the same, the ones I get have a raised dimple that the ground screw threads into so it doesn't stick out the back.

 

[dscheidt]

Not sure if you're trying to be a ****, but that's the only way I saw to do it. I wanted my receptacles the same height as my others and I'm not sure I could get the bends with the offset from the panel without some drop. Unless you mean horizon from the panel, in which case I didn't want my receptacles 6' off the floor. Either way, I've never done it before and I'm satisfied with it.... IMO

You could have done a kicked 90 -- a 90 with a bend orthogonal to the 90, so that the rising part is moved away from the wall the correct distance. Like this: http://www.sawmillcreek.org/showthread.php?229094-Conduit-Bending-101&p=2401347#post2401347

You'd end up with shorter conduit runs, fewer bends, and could probably eliminate that conduit body. Faster to do, looks better, saves wire.

 

[dscheidt]

I was afraid of that... I just hope I can get them with the same offset or I may be rerunning conduit.

Get either an extension, or a deeper mud ring. Either will add depth, and save you from having to replace the box.

 

[PoorOwner]

I have some boxes they don't have the threading for green screw whatsoever, how am I supposed to install a green screw?

I believe self grounding receptacle means if you run a ground wire then you can just attach the ground wire to the receptacle, then it ground the box for you, and then you don't need to bond to the box.
But not the other way around, for example, you don't just install the receptacle (EMT grounded) and assume it has ground, this is wrong, you always have to run the pigtail.
can someone confirm this? How is it OK one way but not the other way.

 

[Marctrees]

Pretty sure Code intends to use seperate grounding screws to bond ground to box than the screws that secure or hold box to any structure.

Even though in real life it would PROBABLY be OK to put under a mounting screw, the Ground screw is independant and will continue it's job of bonding, even if box is falling off the wall for any reason.

Fire, earthquake, your drunk pissed off Uncle w a crowbar, whatever.

Ground will still be bonded to box.

That's the intent of the Code. Marc

 

[Marctrees]

The intent of the code, is more important than SOME technicalitys, unless it is being actually inspected.

Flame me, but keep reading......

The NFPA Natl Code is written by VERY SMART EXPRIENCED folk, after insane study history of structures burning, and many dead people. Marc

 

[wyliesdiesels]

I believe self grounding receptacle means if you run a ground wire then you can just attach the ground wire to the receptacle, then it ground the box for you, and then you don't need to bond to the box.
But not the other way around, for example, you don't just install the receptacle (EMT grounded) and assume it has ground, this is wrong, you always have to run the pigtail.
can someone confirm this? How is it OK one way but not the other way.

you have it backwards.

self grounding means the outlet grounds itself to the box so the outlet doesnt need a pigtail if the box is properly grounded...

yes u can assume the outlet is grounded if its "self-grounding" and the box and EMT is properly grounded.

 

[Cmreschke]

If you plan on using raised covers, you will need a jumper wire from box to receptacle, it won't matter if the receptacle is self grounding or not.

 

[acer66]

If you plan on using raised covers, you will need a jumper wire from box to receptacle, it won't matter if the receptacle is self grounding or not.

Thanks, that is good to know.

 

[dscheidt]

If you plan on using raised covers, you will need a jumper wire from box to receptacle, it won't matter if the receptacle is self grounding or not.

2014 NEC Article 250.146(A). No bonding jumper is required for covers with: (1) Crushed corners
(2) Two or more device attachment screws
(3) A lockwasher or equivalent

 

[RickDel]

Thanks guys. I replaced my boxes with some deeper ones, but now I'm confused on how to secure the #8 AWG THHN to the grounding screw. It's too big. Do I use a lug or some type of crimp connector?

 

[walrus]

Thanks guys. I replaced my boxes with some deeper ones, but now I'm confused on how to secure the #8 AWG THHN to the grounding screw. It's too big. Do I use a lug or some type of crimp connector?

A lug would work

 

[RickDel]

A lug would work

You mean one of these, right?

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[walrus]

You mean one of these, right?

[/URL][/IMG]

Yes

Sent from my SM-G950U using Tapatalk

 

[RickDel]

Ok, thanks!

 

[Cmreschke]

2014 NEC Article 250.146(A). No bonding jumper is required for covers with: (1) Crushed corners
(2) Two or more device attachment screws
(3) A lockwasher or equivalent

Wanna re read that article? Your mistaken I believe.
(A) Surface-Mounted Box. Where the box is mounted on
the surface, direct metal-to-metal contact between the de-
vice 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 con-
tact 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 ex-
posed 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 or nut locking
means and (2) when the cover mounting holes are located
on a flat non-raised portion of the cover.

 

[mm08822]

Wanna re read that article? Your mistaken I believe.
(A) Surface-Mounted Box. Where the box is mounted on
the surface, direct metal-to-metal contact between the de-
vice 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 con-
tact 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 ex-
posed 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 or nut locking
means and (2) when the cover mounting holes are located
on a flat non-raised portion of the cover.

Not my standard practice since the days of bx, but I'm not seeing an issue in his reply. I surely wouldn't use it for 50a recepts.

Raco cut sheet for covers with crushed corners supports it.......

http://www.hubbell-rtb.com/p-24-4-in-square-exposed-work-covers

 

[Cmreschke]

My first question would be if the cover is LISTED for grounding and bonding. Are the screws threadlocking?

 

[dscheidt]

My first question would be if the cover is LISTED for grounding and bonding. Are the screws threadlocking?

If you use the hardware that comes with the plate, they're listed for the purpose. (It's actually the nut that's important, it's got a buiit in serrated lock washer.)

Someone is making plates that don't come with a bag of hardware, but have nuts stamped into the void where the device goes. I doubt they're listed that way. They showed up in stores here briefly a year or so ago.