grounding boxes

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fireryan

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Why do we need to put ground pigtails to a metal box. If the outlet has a ground on it isnt it also grounding the box through the yoke. Have always wondered this
 
fireryan said:
Why do we need to put ground pigtails to a metal box.
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I do because of this:

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).
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) Connections. Connections and splices shall be made in accordance with 110.14(B) except that insulation shall not be required.
(B) Grounding Continuity. The arrangement of grounding connections shall be such that the disconnection or the removal of a receptacle, luminaire, or other device fed from the box does not interfere with or interrupt the grounding continuity.
(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, equipment listed for grounding, or a listed grounding device.
(D) Nonmetallic Boxes. One or more equipment grounding conductors brought into a nonmetallic outlet box shall be arranged such that a connection can be made to any fitting or device in that box requiring grounding.
(E) Solder. Connections depending solely on solder shall not be used.
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This graphic may help you visualize why it is so. As stated by Barbeer the sheetrock would interrupt the contact.

1100207566_2.jpg
 
chris kennedy said:
Dennis, was OP asking about grounding a box or device?
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Looks like the op was saying why bond the box using a bonding jumper, when you can bond the box using the yoke of a device that has an ECG attached.
 
Okay I guess the graphic wasn't enough. The box is what needs bonding at all times otherwise when you remove the device the box would not be grounded. The graphics show when the recep/device would not need grounding.
 
Flex said:
So you would lose the ground if you removed the device
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Why is the device removed? If it's out of the box and still live, you have bigger things to be worried about than loss of ground continuity.

Flex said:
and the yolk broke contact with the box
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Not a problem unless you normally leave your receptacles loose on a surface mounted box. ;)
 
resistance said:

when you can bond the box using the yoke of a device that has an ECG attached.
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I see that. I was trying to point out to Dennis he was confusing 250.148 and 250.146. That happens when you get to his age.
 
peter d said:
Why is the device removed? If it's out of the box and still live, you have bigger things to be worried about than loss of ground continuity.



Not a problem unless you normally leave your receptacles loose on a surface mounted box. ;)
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Doesnt a bonded box cover all angles instead of counting on the yolk which only works when attatched to box. Or on an industrial raised ring if you pull the ring you lose the bond.
 
Flex said:
Doesnt a bonded box cover all angles instead of counting on the yolk which only works when attatched to box. Or on an industrial raised ring if you pull the ring you lose the bond.
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The NEC permits metal to metal contact in lieu of a wire EGC in both of those cases. Again your arguments don't hold water because a loose raised cover has other issues besides lack of grounding continuity.
 
chris kennedy said:
I see that. I was trying to point out to Dennis he was confusing 250.148 and 250.146. That happens when you get to his age.
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So what is it called when you are young.....(don't answer this);) ;) :D
 
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