Ground 4" Metal Boxes?

[flyfish13]

I am wiring my 30x40 metal shop with new 200 amp service. All wiring is in 1/2" and 3/4" EMT to 4" metal square boxes. My question is am I required to ground each 4" metal box (to the ground wire running to each box)?

 

[MrMark]

No, but I would.

 

[kbs2244]

Are you confusing ground and neutral?

With EMT there is no ground wire.
The EMT acts as the ground.

The neutral is the white wire, it is not a ground.
The white wire should not be attached to the box.

I would strongly suggest some reading.

 

[sparky36000]

Are you confusing ground and neutral?

With EMT there is no ground wire.
The EMT acts as the ground.

The neutral is the white wire, it is not a ground.
The white wire should not be attached to the box.

I would strongly suggest some reading.

It's not always required, there are a few exceptions though. But it is very commonly done and the OP sounds like he is installing them. That being said, if there are splices in the box, yes you have to bond the box. If no splices and just used as a pull box, you are not required to break the EGC to bond the box.

 

[flyfish13]

It's not always required, there are a few exceptions though. But it is very commonly done and the OP sounds like he is installing them. That being said, if there are splices in the box, yes you have to bond the box. If no splices and just used as a pull box, you are not required to break the EGC to bond the box.

There will be spices in many of the overhead boxes. If I am understanding you correctly, if there are splices in the boxes then I need to ground the box to the ground wire going back to my breaker box. What about the boxes that house the outlets at the end of a "run"? There will be no splices. The Ground/Neutral/Hot wires will go directly to the plugs. Am I required to ground these?

 

[flyfish13]

Are you confusing ground and neutral?

With EMT there is no ground wire.
The EMT acts as the ground.

The neutral is the white wire, it is not a ground.
The white wire should not be attached to the box.

I would strongly suggest some reading.

I am not confused with the difference between neutral/ground. I am asking if the ground (green wire) should be attached to my 4" metal boxes.

 

[sparky36000]

What about the boxes that house the outlets at the end of a "run"? There will be no splices. The Ground/Neutral/Hot wires will go directly to the plugs. Am I required to ground these?

Yes, those devices are considered splices since the conductors don't pass thru the box unbroken.

Here's the code for it:
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).

 

[Burgerkong]

Here's how I did them:

http://www.garagejournal.com/forum/showthread.php?t=211182

I bonded all my boxes whenever a splice occurred (receptacle, wire nut etc). If the wires are just passing through the box, there's no need for additional grounding/bonding.

 

[flyfish13]

Here's how I did them:

http://www.garagejournal.com/forum/showthread.php?t=211182

I bonded all my boxes whenever a splice occurred (receptacle, wire nut etc). If the wires are just passing through the box, there's no need for additional grounding/bonding.

Yes, those devices are considered splices since the conductors don't pass thru the box unbroken.

Here's the code for it:
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).

That answers my question. Thanks for the info.

 

[zmaxmotorsports]

Yes, those devices are considered splices since the conductors don't pass thru the box unbroken.

Here's the code for it:
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).

 

[kbs2244]

I apologize to the OP.
I have never seen a green wire in an EMT installation.

 

[lbmcse]

I am wiring my 30x40 metal shop with new 200 amp service. All wiring is in 1/2" and 3/4" EMT to 4" metal square boxes. My question is am I required to ground each 4" metal box (to the ground wire running to each box)?

In a word, yes. All metallic components of a wiring system, including raceways, boxes and devices shall be grounded. The green wire (the equipment grounding conductor) should be bonded to every box in the system.

 

[Speedy Petey]

Yes, those devices are considered splices since the conductors don't pass thru the box unbroken.

Here's the code for it:
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).

Like has been stated, THIS is the correct answer.

 

[alan camby]

"shall be connected within the box or to the box"
So is it ok to run the ground to the device only, say the receptacle, and let the device cary ground contact to the box thru the screws.

How about if I just ground the box. Are the screws considered to be a good enough connection from the box to the receptacles/device?

BTW..I have always grounded the box and the ground screw on the device.

I assume the op is using wire (THHN) instead of romex thru the conduit. If he was running Romex, the bare ground would already be in the cable. Is there anything wrong with running Romex in metal conduit?

 

[Burgerkong]

"shall be connected within the box or to the box"
So is it ok to run the ground to the device only, say the receptacle, and let the device cary ground contact to the box thru the screws.

How about if I just ground the box. Are the screws considered to be a good enough connection from the box to the receptacles/device?

BTW..I have always grounded the box and the ground screw on the device.

I assume the op is using wire (THHN) instead of romex thru the conduit. If he was running Romex, the bare ground would already be in the cable. Is there anything wrong with running Romex in metal conduit?

It accounts for the scenario where you use pigtails to connect your device/receptacle/switch. In that case, your pigtail has to have a splice where another pigtail from the ground screw on the box connects to.

Regarding Romex/NMB90, the way I understood it was that it's sheathing acts as another thermal insulator, so if it was run with its sheathing inside a small diameter pipe, it heats up much quicker and hotter than just a THHN conductor. As a result, there is a higher risk of fire because the insulation isn't rated for the elevated temperatures.

I believe I linked my thread earlier on, but it's fairly kosher electrical wise (aside from the small boxes, while at the box fill limit, is a PITA to work out of).

 

[Charles (in GA)]

"shall be connected within the box or to the box"
So is it ok to run the ground to the device only, say the receptacle, and let the device cary ground contact to the box thru the screws.

How about if I just ground the box. Are the screws considered to be a good enough connection from the box to the receptacles/device?

BTW..I have always grounded the box and the ground screw on the device.

I assume the op is using wire (THHN) instead of romex thru the conduit. If he was running Romex, the bare ground would already be in the cable. Is there anything wrong with running Romex in metal conduit?

If you look at a receptacle, it will have one of the two screws "captive" in either a funny wire bale or a slightly bent metal tab that is riveted to the yoke. These small devices are there to insure a positive contact between the yoke of the device (which is connected to the ground pin and the ground screw tab) and the box itself.

With respect to Romex® in conduit, NEC requires that "A multi-conductor cable or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage of conduit fill area.", which means a fill % of 53%, somewhat higher than the 31% for two conductors and 40% for three or more conductors. It does however require that you calculate the total cross sectional area "For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter."

So you gain a little on the percentage of fill, and lose on the cross sectional area calculation.

Charles

 

[Gooch]

Also need to ground the box if you are using any concentric knockouts.(I.E. 1/2 emt through a hole in the box that can be knocked out to 3/4)

 

[Speedy Petey]

"shall be connected within the box or to the box"
So is it ok to run the ground to the device only, say the receptacle, and let the device cary ground contact to the box thru the screws.

NO. The box MUST be solidly bonded to the grounding conductor. The device cannot ground the box.
The box can ground the device in some instances though.

 

[sparky36000]

Also need to ground the box if you are using any concentric knockouts.(I.E. 1/2 emt through a hole in the box that can be knocked out to 3/4)

If your using a supplemental equipment grounding conductor you have to bond the box. But if your using the EMT as the EGC and the box is listed for grounding using the concentric ko's(wich most 4 square boxes are) with the correct fittings, no additional bonding is required. This is a piece of misinformation I have heard many times over the years. Again, here's the code.

250.97 Bonding for Over 250 Volts. For circuits of over
250 volts to ground, the electrical continuity of metal raceways
and cables with metal sheaths that contain any conductor
other than service conductors shall be ensured by
one or more of the methods specified for services in
250.92(B), except for (B)(1).

Exception: Where oversized, concentric, or eccentric knockouts
are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a
reliable bonding connection, the following methods shall be
permitted:
(1) Threadless couplings and connectors for cables with
metal sheaths
(2) Two locknuts, on rigid metal conduit or intermediate
metal conduit, one inside and one outside of boxes and
cabinets
(3) Fittings with shoulders that seat firmly against the box
or cabinet, such as electrical metallic tubing connectors,
flexible metal conduit connectors, and cable connectors,
with one locknut on the inside of boxes and
cabinets
(4) Listed fittings
250.98

 

[pattenp]

The code section 250.97 you have listed is for over 250V. The applicable section is 250.96.

If your using a supplemental equipment grounding conductor you have to bond the box. But if your using the EMT as the EGC and the box is listed for grounding using the concentric ko's(wich most 4 square boxes are) with the correct fittings, no additional bonding is required. This is a piece of misinformation I have heard many times over the years. Again, here's the code.

250.97 Bonding for Over 250 Volts. For circuits of over
250 volts to ground, the electrical continuity of metal raceways
and cables with metal sheaths that contain any conductor
other than service conductors shall be ensured by
one or more of the methods specified for services in
250.92(B), except for (B)(1).

Exception: Where oversized, concentric, or eccentric knockouts
are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a
reliable bonding connection, the following methods shall be
permitted:
(1) Threadless couplings and connectors for cables with
metal sheaths
(2) Two locknuts, on rigid metal conduit or intermediate
metal conduit, one inside and one outside of boxes and
cabinets
(3) Fittings with shoulders that seat firmly against the box
or cabinet, such as electrical metallic tubing connectors,
flexible metal conduit connectors, and cable connectors,
with one locknut on the inside of boxes and
cabinets
(4) Listed fittings
250.98

 

[sparky36000]

The code section 250.97 you have listed is for over 250V. The applicable section is 250.96.

250.96 only mentions ensuring electrical continuity, 250.97 is the only section that mentions concentric KO's, and yes it is for over 250v to ground. I guess my point is I've heard guys say you have to bond around concentric KO's like the previous poster mentioned. Most 4 square general purpose boxes are listed and approved for electrical continuity thru concentric KO's.

This is from the RACO website:
Independent tests conducted by UL prove that the TKO® passes the same high-current fault test used to test grounding bushings and ground lugs
RACO® TKO® knockout is UL Listed, providing bonding without the use of bonding jumpers
Suitable for bonding without any additional bonding means around concentric (or eccentric, TKO) knockouts where used in circuits above or below 250V.

 

[Charles (in GA)]

250.96 only mentions ensuring electrical continuity, 250.97 is the only section that mentions concentric KO's, and yes it is for over 250v to ground. I guess my point is I've heard guys say you have to bond around concentric KO's like the previous poster mentioned. Most 4 square general purpose boxes are listed and approved for electrical continuity thru concentric KO's.

This is from the RACO website:
Independent tests conducted by UL prove that the TKO® passes the same high-current fault test used to test grounding bushings and ground lugs
RACO® TKO® knockout is UL Listed, providing bonding without the use of bonding jumpers
Suitable for bonding without any additional bonding means around concentric (or eccentric, TKO) knockouts where used in circuits above or below 250V.

Good info to know. Will have to file this in the memory bank for the next discussion where this comes up.

Charles