Three threads

[ptonsparky]

CH EG bars use two self threading screws to attach them to the loadcenter enclosure. The predrilled holes are not deformed in anyway. Individually the screw will not allow for the 3 threads required. Are they getting by this requirment by using two screws?

May I apply this same method when field installing ground bars in the field?

Locally my inspectors are happy with about any ground screw but what about the rest of you.

 

[rcarroll]

Individually the screw will not allow for the 3 threads required.

wsquote] Where are you getting this from? I'd say your install is ok providing you're not using sheet metal screws. 250.8

 

[don_resqcapt19]

Where is there a rule that calls for 3 threads? This is part of listed equipment and whatever screw that was used in the listing process is acceptable.
Don

 

[petersonra]

i have heard this three thread rule repeated so often that I am almost starting to believe it.

 

[raider1]

The 2008 NEC section 250.8(A) requires that machine screws and thread forming screws, used to connect grounding conductors and bonding jumpers, engage not less than 2 threads. Here is what that section says:

250.8 Connection of Grounding and Bonding Equipment.
(A) Permitted Methods. Grounding conductors and bonding
jumpers shall be connected by one of the following
means:
(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

Chris

 

[LarryFine]

i have heard this three thread rule repeated so often that I am almost starting to believe it.

Oh, sure. Next thing we know, you'll believe that you must have a pull-point every 100 feet. :grin:

 

[ptonsparky]

Excuse me "two threads".

The point of the question is, was, am I required to use one thread forming screw to get "X"# of threads or may I use two screws to accomplish 250.8(6)? Thank you Chris.

For the sake of this project I have only two ground screws, a box wall thickness that allows only 1 1/2 thread, I dropped my last nut into 6 inches of manure and none of the other 7 options available.

 

[Dennis Alwon]

I dropped my last nut into 6 inches of manure and ...

That must have hurt. :grin:

 

[jim dungar]

The point of the question is, was, am I required to use one thread forming screw to get "X"# of threads or may I use two screws to accomplish 250.8(6)? Thank you Chris.

You must comply with the NEC. The manufacturer has the ability to have their equipment tested and then listed.

 

[LarryFine]

. . . a box wall thickness that allows only 1 1/2 thread . . .

Get a finer-pitched screw. :smile:

 

[Dennis Alwon]

The predrilled holes are not deformed in anyway. Individually the screw will not allow for the 3 threads required. Are they getting by this requirment by using two screws?

May I apply this same method when field installing ground bars in the field?

I don't see how using 2 non compliant threaded holes would make the install compliant. If you are asking what I would do and there aren't any other options then I would probably just use one screw and hope for the best.

I hate admitting that I am not perfect. Don't tell my wife she doesn't know yet. :grin:

 

[raider1]

Excuse me "two threads".

The point of the question is, was, am I required to use one thread forming screw to get "X"# of threads or may I use two screws to accomplish 250.8(6)? Thank you Chris.

For the sake of this project I have only two ground screws, a box wall thickness that allows only 1 1/2 thread, I dropped my last nut into 6 inches of manure and none of the other 7 options available.

Youe Welcome,

If the equipment grounding bar is a listed piece of equipment then you must install it according to the manufactures instructions.

I don't believe that the NEC allows the use of two screws with only 1 1/2 threads engaged to meet the requirments of 250.8(A) unless they are part of a listed assembly or other listed means.

Chris