# Understanding the bond screw



## bluebird5

I do not understand when to and when not to use the bond screw in panels. I the panel is a subpanel it goes in on the ground side to bond the panel to ground incase it ever got charged right? If the panel does not have the ground and neutral isolated do you need the bond screw. It just seems to me like you would use it every time to bond the panel to to the neutral or ground.


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## Seven-Delta-FortyOne

On most panels, the grounding bar is already bonded to the case. The grounding screw is there to connect the neutral and ground together, only at a main panel. On sub-panels, the neutral and ground are isolated.


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## 480sparky

As a general rule, after the first point of disconnect, you need to separate the neutral & ground conductors. If you don't use the panel as the FPOD, then you do not use the bonding screw.


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## bluebird5

ok so main panel use it. Subpanel don't use it. What is the purpose of bonding the panel to the neutral bar?


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## 480sparky

bluebird5 said:


> ok so main panel use it. Subpanel don't use it. What is the purpose of bonding the panel to the neutral bar?


Because, in a main panel, the neutral is the conductor that will carry any fault current the box has back to the source of power, allowing the breaker to open properly.

In a subpanel, the ground wire performs that duty.


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## SemiRetiredEL

As was already mentioned, with few exceptions, the neutral and the ground buss can only be tied together at the service disconnect.

But, every metal enclosure is required to be grounded/bonded but a ground screw is not the only method (2011 NEC):

250.8 Connection of Grounding and Bonding Equipment. 

Changed From 2008 

•250.8: Revised to include specific reference to grounding electrode conductors and to delete reference to grounding conductor. 

(A) Permitted Methods. Equipment grounding conductors, grounding electrode conductors, and bonding jumpers shall be connected by one of the following means: See related UL 

(1) Listed pressure connectors 

(2) Terminal bars 

(3) Pressure connectors listed as grounding and bonding equipment 

(4) Exothermic welding process 

(5) Machine screw-type fasteners that engage not less than two threads or are secured with a nut 

(6) Thread-forming machine screws that engage not less than two threads in the enclosure 

(7) Connections that are part of a listed assembly 

(8) Other listed means


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## Philby

1st time on site. Love that quote! Going to use it.


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