Clarification of Bonding Issue

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  #1  
Old 03-08-07, 10:41 PM
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Clarification of Bonding Issue

If I understand NEC 250.146 and 250.148 correctly, then a separate equipment bonding jumper is required for each metal gang box connected together, and for which there is a corresponding branch circuit and associated receptacle or switch.

For example, if I have three metal switch boxes that I connect together, each with a separate branch circuit from the service panel, and each circuit with a separate switch, then a separate bonding jumper is required between each switch box and its switch, and connected to the corresponding branch circuit ground conductor.

In this way, even if one of the switches is removed, the grounding continuity is not interrupted.

Is this correct?

Thanks!
 
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  #2  
Old 03-09-07, 02:45 AM
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I am confused by your post. How do you mean the boxes are "connected together"? By a raceway? Cable? Gangable boxes?

The bottom line is first and foremost a metallic box must be grounded. Regardless of how it is done, it must be grounded.
This ground must NOT rely on a device. Meaning the device cannot ground the box, and removal of the device must not impede this ground.

All grounds in a box must be connected. There are odd exceptions but this is a general rule. So even if there two (or more) branch circuits in a given box all the grounds must be spliced.

There are different rules for different devices as well. In a metallic box a switch does not need a bonding jumper. The connection to the box is adequate.
For receptacles in a metallic box it must be a self grounding type to omit the bonding jumper.
ALL devices in non-metallic boxes require bonding jumpers (with few exceptions).
 
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Old 03-09-07, 03:20 AM
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I believe that the question is if each gang of a gangable box needs its own ground tail.????

I do not think that the code says one way or another. The answer to the question is what the mfg says in the listing and labling.

this is alot like the control panels I build. Sometimes the Panel is listed to carry the ground, and sometimes it is not. If it is not, one needs a ground bar or many wire lug. If the panel can carry the ground, then one can use several single wire lugs. (just to be pedantic, an enclosure is box shaped with a cover, and Panel fits inside an enclosure and has the devices mounted to it.)

I have never researched this, but I have never used more than one ground screw no matter how many gangs I have assembled.
 
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Old 03-09-07, 02:28 PM
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****More Information

Thank you both for responding.

To clarify, yes, I am talking about metal switch boxes ganged together.

Speedy, when you say "all the grounds must be connected", do you mean that all the individual ground conductors from each circuit must be tied together?

Which option?

Option #1

From/To panel From/To light fixture

Circuit A ground -----------+---------- Circuit A ground
|----(pigtail)------ [switch A]
Circuit B ground -----------+---------- Circuit B ground
|----(pigtail)------ [switch B]
Circuit C ground -----------+---------- Circuit C ground
|----(pigtail)------ [switch C]
Equip. bnd. jmpr ----------+


Option #2

From/To panel From/To light fixture

Circuit A ground -----------+---------- Circuit A ground
|---------- [switch A]
Equip. bnd. jmpr ----------+

Circuit B ground -----------+---------- Circuit B ground
|---------- [switch B]
Equip. bnd. jmpr ----------+

Circuit C ground -----------+---------- Circuit C ground
|---------- [switch C]
Equip. bnd. jmpr ----------+


Or, if no equipment bonding jumper is needed for the switches:

Option #3

From/To panel From/To light fixture

Circuit A ground -----------+---------- Circuit A ground
|----(pigtail)------ [switch A]
Circuit B ground -----------+---------- Circuit B ground
|----(pigtail)------ [switch B]
Circuit C ground -----------+---------- Circuit C ground
|----(pigtail)------ [switch C]

Option #4

From/To panel From/To light fixture

Circuit A ground -----------+---------- Circuit A ground
|---------- [switch A]

Circuit B ground -----------+---------- Circuit B ground
|---------- [switch B]

Circuit C ground -----------+---------- Circuit C ground
|---------- [switch C]


Sorry for the long post. Hope these "diagrams" appear correctly on your screen.

Thanks!
 

Last edited by rdn2113; 03-09-07 at 03:29 PM.
  #5  
Old 03-09-07, 05:20 PM
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I'm really sorry but I do not get those diagrams at all. Very nice effort though. I wish I understood.



In any case.

"Speedy, when you say "all the grounds must be connected", do you mean that all the individual ground conductors from each circuit must be tied together?"

Yes, that is exactly what I mean. But at the same time, NO, each box "section" does not need a bonding jumper. One connection is fine.
 
  #6  
Old 03-09-07, 07:05 PM
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****One More Try

I apologize for the diagrams Speedy - they looked OK until I posted them, then everything moved over to the left. Sorry!

Let's see if this works. Is this correct? (the + signs mean "connected to")

[Crkt-A-Gnd-In] + [Pigtail-to-Switch-A] + [Crkt-A-Gnd-Out]
+ [Pigtail] +
[Crkt-B-Gnd-In] + [Pigtail-to-Switch-B] + [Crkt-B-Gnd-Out]
+ [Pigtail] +
[Crkt-C-Gnd-In] + [Pigtail-to-Switch-C] + [Crkt-C-Gnd-Out]
+
[Equipment-Bonding-Jumper-to-Gang-Box]

Thanks for your patience and help!
 
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