GROUND SCREWS IN METAL JUNCTION BOXES

[garrosan]

Hi guys. I am an apprentice with a question that I have received varying answers. Do metal junction boxes require a grounding screw with pigtail? Several Journeymen have stated that if you run metal conduit, the conduit is considered grounded, thus a ground screw in every j-box is not required (the same answer applies if you're running MC cable). However, 1 guy (the one who I first started with says they are required). I spent 20 years in the US Navy onboard Nuclear Submarines. The manuals for operating a nuclear power plant are not as confusing as the NEC 2002. I do not know if a definitive answer is a viable option but anything would help, especially a code reference. Thanks guys.

 

[ryan_618]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

See 250.148(A)

(A) 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.

Edited to include reference.

[ May 09, 2004, 12:16 PM: Message edited by: ryan_618 ]

 

[garrosan]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

Thanks. I read that also. o you have any idea where these other guys came up with thier idea that the conduit fulfills the requirement of the ground?

 

[iwire]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

It is not as clear as yes or no.

If you have metal raceway with metal boxes and you do not have spliced or terminated conductors within the box you do not have to install the grounding pigtail.

So a true pull box is not required to have a grounding pigtail. Make it a junction or device box and the box must be connected to the grounding conductor.

 

[tom baker]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

Section 250.118 lists the allowed equipment grounding (bonding) conductors, which allows metal raceway, AC cable, MC cable..... A seperate green wire is not required by the NEC in a metal raceway, but it may be a good idea.

 

[iwire]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

Conduit is a listed grounding conductor.

You can choose not to run a separate copper grounding conductor

Then you would need a jumper from the box to receptacles also.

 

[tom baker]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

Garosan: you understand nuclear power plants because the navy sent you to school for your rate, nuclear power school, prototype and then to the fleet. If you just jumped into the NEC you have problems with it. I recommend a book by the NFPA "Users Guide to the NEC", and then Vol 1 and 2 of Mike Holts Understanding the NEC
I was in the navy as a mechnical operator and made the tranistion to a electrican with no problems.
Tom Baker, Class 70-4.

 

[russ]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

With metal boxes and metal conduit, 250.146 (A) (B) and (C) allows some devices to be installed with out a wire grounding jumper.
In my area, we mostly use metal conduit and grounding is done a great deal of the time with listed self grounding devices, and no jumper.

 

[iwire]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

Still you will need to ground the box.

 

[russ]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

Bob, I'm not sure what you mean. 358.2 says EMT can be use as an equipment grounding conductor when installed utilizing appropriate fittings.
The box would already be grounded.

 

[iwire]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

I am sorry, I meant if there is a grounding conductor pulled in the raceway, you would need to connect it at each box even with self grounding receptacles.

 

[russ]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

250.148(A)
Just so I understand what you mean, let me ask this. If an equipment grounding conductor is pulled in the EMT for attachment to the receptacle(s), it should be fastened to the box as well as the receptacle(s).
Would connecting the ground wire to the receptacle, and the fasting the self grounding receptacle to the box eliminate the need for the jumper fastened to the box?

 

[pierre]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

Russ
Connecting the EGC to the device and then to the box would not meet this requirement- what happens to the grounding connection if the device is removed from the box during work?

Pierre

 

[brentp]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

If I 'choose' to install a grding coductor along with a metal raceway, why 'must' I attach the egc to all the metal junction boxes? The boxes are already bonded by means of the metal raceway.

Brent

 

[ryan_618]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

Russ: The box must be bonded. If you have an EGC, you must attach it to the box. If your receptacle outlet is mounted via faceplate (such as an industrial cover or raised stell), you must pigtail to it as well.

I don't have my NEC handy...can someone validate my last reply with a reference please?

 

[iwire]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

Bonding the box and the outlet are two sperate issues.

Here is some code for the outlet.

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).

(A) Surface Mounted Box. Where the box is mounted on the surface, direct metal-to-metal contact between the device yoke and the box shall be permitted to ground the receptacle to the box. 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.

(B) Contact Devices or Yokes. Contact devices or yokes designed and listed for the purpose 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 required 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 grounded by an insulated equipment grounding conductor run with the circuit conductors. This grounding conductor shall be permitted to pass through one or more panelboards without connection to the panelboard grounding terminal as permitted in 408.20, 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.

Now for the boxes

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 separate equipment grounding conductors associated with those circuit conductors shall be spliced or joined within the box or to the box with devices suitable for the use. Connections depending solely on solder shall not be used. Splices shall be made in accordance with 110.14(B) except that insulation shall not be required. The arrangement of grounding connections shall be such that the disconnection or the removal of a receptacle, luminaire (fixture), or other device fed from the box will not interfere with or interrupt the grounding continuity.

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) 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.

(B) Nonmetallic Boxes. One or more equipment grounding conductors brought into a nonmetallic outlet box shall be arranged so that a connection can be made to any fitting or device in that box requiring grounding.

 

[pierre]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

As Bob has stated, I think that .148 is what Ryan is asking for.

Pierre

 

[iwire]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

I think this thread keeps going back and forth between box and outlet grounding, both of which are important and do not have straight yes or no answers.

The company I work for keeps it easy.

All devices always have grounding conductors attached, self-grounding or not.

All branch circuit boxes are grounded.

Some large feeder pull boxes will not get bonded, if we pull right through.

 

[garrosan]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

OK guys, thanks for the wonderful responses. Bob, please correct my summation:

1) All junction boxes will require a grounding screw "if" there are any splices in, or devices attached to that box.

2) Metal conduit (raceway) with the approved fittings can be considered grounded, thus eliminating the requirement for pulling a seperate circuit ground, but not eliminating the requirement of the grounding screw.

 

[russ]

Re: GROUND SCREWS IN METAL JUNCTION BOXES

OK 250.148(A) requires you to, bond a wire equipment ground, to the box if it's for circuit conductors described in 250.148, even if it's in EMT.