Bonding screw on new panel

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  #1  
Old 11-03-02, 01:24 PM
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gwenzel
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Bonding screw on new panel

I've just replaced the main fuse box in the house with a 100 amp breaker box. The nuetral/ground bar is bonded to the water pipe and an external ground rod. My question is do I install the green ground screw in the box to bond the box to the ground bar?
 
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Old 11-03-02, 01:28 PM
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Assuming the rest of this setup is correct, then the answer is yes. (Actually, the screw bonds the neutral bar to the box, not the grounding bar. The grounding bar should already be connected to the box.)
 
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Old 11-03-02, 01:31 PM
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Why is the panel sold without the screw installed, in other words when would you not install it?
 
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Old 11-03-02, 01:40 PM
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The screw is only installed in a panel that also contains the main disconnect. The most common reason to throw the screw away is for a subpanel, but you also throw it away if you have an external disconnect.
 
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Old 11-03-02, 01:41 PM
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Ok, Thanks for your help.
 
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Old 11-03-02, 01:43 PM
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By external disconnect are you refering to something like an A/C disconnect mounted near the condensor outside?
 
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Old 11-03-02, 01:49 PM
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I'm referring to something that shuts off all power in your house. For most people, that's the main breaker in their main panel.
 
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Old 11-03-02, 01:52 PM
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Ok, Thanks
 
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Old 11-03-02, 02:21 PM
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To bond or not to bond

Originally posted by gwenzel
"Why is the panel sold without the screw installed, in other words when would you not install it?"

The simple version of the answer is that the buss bar for the grounded circuit conductors is bonded to the service equipment enclosure and to the enclosure of the building disconnecting means of other buildings supplied from the same service when no Equipment Grounding Conductor (EGC) was run with the feeder conductors but it is not bonded to any other panel cabinet.

Since the reasons this is true are not obvious what follows is the rest of the story.

Panels are built with a removable bonding screw or strap to permit their use as "Service Equipment" or as feeder supplied panels were a ground is run with the feeder conductors.

Service Equipment is defined in the US NEC as. The necessary equipment, usually consisting of a circuit breaker(s) or switch(es) and fuse(s) and their accessories, connected to the load end of service conductors to a building or other structure, or an otherwise designated area, and intended to constitute the main control and cutoff of the supply.

If the panel is to be installed as Service Equipment then the bonding screw or strap is installed in order to bond the grounded conductor of the service conductors to the cabinet. That cabinet then serves as the service equipment enclosure.

If the panel is to be installed as a feeder supplied power or lighting and appliance panel board with an Equipment Grounding Conductor run with the feeder supplying it you would not install the screw that would bond the grounded conductor of the feeder to the cabinet that encloses the panel assembly. You would install a separate buss for the termination of equipment grounding conductors. The screws that are used to mount these separate add on grounding busses bond them to the panel's cabinet without the use of the additional bonding screw.

In some brands of panel the original built in buss bar can be separated in half with one half bonded to the panel cabinet and the other not bonded. In those types of panel you just remove the jumper bar that connects the two halfs of the buss together and terminate all of the EGCs to the bonded half of the buss bar and all of the grounded circuit conductors to the other insulated buss bar half if the panel is not going ot be used as service equipment.
--
Tom
 

Last edited by hornetd; 11-05-02 at 04:03 PM.
  #10  
Old 11-03-02, 04:12 PM
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Smile

Tom, that's the "simple version of the answer"?

John
 
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Old 11-05-02, 11:43 AM
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Originally posted by John Nelson
"Tom, that's the "simple version of the answer"?

John "

Yea, I know, but that first paragraph contains the simplest answer I cound devise.
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Tom
 
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