Three threads

Status
Not open for further replies.
ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
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.
 
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
 
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
Click to expand...

Chris
 
petersonra said:
i have heard this three thread rule repeated so often that I am almost starting to believe it.
Click to expand...
Oh, sure. Next thing we know, you'll believe that you must have a pull-point every 100 feet. :grin:
 
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.
 
ptonsparky said:
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.
Click to expand...

You must comply with the NEC. The manufacturer has the ability to have their equipment tested and then listed.
 
ptonsparky said:
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?
Click to expand...

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:
 
ptonsparky said:
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.
Click to expand...

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
 
Status
Not open for further replies.
Top