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Sheet metal screws

Mark K said:
Why? What are the issues?
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See #6

250.8 Connection of Grounding and Bonding Equipment.
(A) Permitted Methods.
Equipment grounding conductors, grounding electrode conductors, and bonding jumpers shall be connected by one or more 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
 
Racking manufactures have specific installation instructions for the use of lay-in lugs. That usually includes a star washer and a specific location on the racking. Many have proprietary hardware for mounting a lay-in lug or a different terminal altogether.

250.8 Connection of Grounding and Bonding Equipment.
(A) Permitted Methods. Equipment grounding conductors, grounding electrode conductors, and bonding jumpers shall be connected by one or more 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

Note that sheet metal screws are not included and #s 5&6 state that two threads be engaged.
 
ICE said:
Note that sheet metal screws are not included and #s 5&6 state that two threads be engaged.
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Which normally a sheet metal screw would not meet, but that aluminum rail has a thick enough wall that perhaps it does. You'd have to compare the rail wall thickness to the thread pitch to determine if there's a 250.8(A) violation.

That said, if the rail or lay-in-lug instructions specify a different type of fastener, that would be a 110.3(B).

Cheers ,Wayne
 
wwhitney said:
Which normally a sheet metal screw would not meet, but that aluminum rail has a thick enough wall that perhaps it does. You'd have to compare the rail wall thickness to the thread pitch to determine if there's a 250.8(A) violation.

That said, if the rail or lay-in-lug instructions specify a different type of fastener, that would be a 110.3(B).

Cheers ,Wayne
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What about the part that says "machine type fasteners?" What was the intent of that?
 
jar546 said:
What about the part that says "machine type fasteners?" What was the intent of that?
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I think you mean "machine screw-type fasteners." Not sure of the intention, but that's a sufficiently awkward and non-standard phrase that I find it reasonable to read it to cover sheet metal screws.

BTW, I just noticed that 250.8(A)(6) mentions an "enclosure". So I guess I agree that 250.8(A)(6) is not an option for the OP, just 250.8(A)(5). And if your interpretation is that a sheet metal screw is not a "machine screw-type fastener," then you have a 250.8(A) violation.

Cheers, Wayne
 
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