i have a 3 phase 480/277 panel i wanted to bond to the building steel. which metal roof rafters that support the roof. is it ok to drill and 1/4x20 a lug or ive heard of a lug that the head of the bolt snaps off at the right torqe? which one would be legal

Are you bonding the Building Steel to the Electrical system via a connection at the Sub Panel, or are you planning to ground the Sub Panel by bonding it to the grounded Building Steel?

If Bonding the Steel to the Grounded Electrical System, then do so via approved lugs and bolt sizes according to the lug. Torque all to the specifications only ONCE!!! Do not re-torque the lug.
If the bolt used to land the lug snaps off when torqued, find a better bolt!
Maybe someone can suggest what to do here. I have broke bolts during torquing, but they were few and far between [and sometimes the "Cheap'os" from the Home Depot's open bins].

Lugs have been known to strip out during torquing. Can't really elaborate much on this one except that "Doo-Doo Occurs"

Now, if you are planning to ground bond a panel by connecting it to a grounded Steel frame, this would be something that falls under 250-32.
Could you expand a little more on your topic?

Scott SET

2002 NEC, 250.53(C) Shall be connected in a manner specified in 250.70.
(exothermic welding,listed lugs,listed pressure connectors,listed clamps,or other listed means,Connections depending on solder shall not be used.
If the lug is listed for the wire property on the connection to the steal, than it can be connected to the building by the 1/4*20 screw, locknuted and torqed to the bolts manufacture standards. as long as any paint or primer is removed from the building steal first.
To insure a good connection than it would be recommended to install a min. (hex head bolt). and torqued.
A illegal connection would be with a self drilling screw...
As far as the other lug, again, as long as it is listed... (You are using for the purpose it is intended for.)

Yes there are torque indicating bolts and adapters that are designed to "twist-off" at the correct torque. These negate the need for a torque wrench.

Check out Ilsco and Burndy, I believe they both have adapters that go between a normal wrench and a socket. For dual headed twist-off bolts try Fastenal.

aphares,
Is a self drilling screw always sheet metal screw? There are self-drilling, self taping machine screws that would be permitted for grounding connections.
Don(resqcapt19)

My interpatation:
A sheet metal screw has threads that tear the metal than set their self by force. A self tapping screw would tap the threads in to the metal and could be screwed to a specific toque. The tapping screw would be legal. You are correct.....

Most enclosures that may be used where an EGC is installed will have a termination point such as one with a lug, or "a means provided" and this may be a simple "hump with a thread" to be used with a machine screws, and not a sheet metal screw.

Any kind of a "sheet metal screw" is not permitted.


[This message has been edited by Joe Tedesco (edited 12-24-2001).]

Joe,
What is the definition of a "sheet maetal screw" and where do we find it. I know that the intent is to provide a secure electrical connection, but when you look in a hardware catalog you will find that the ones in your pictures are not shown as "sheet metal screws". Look at: http://www.mcmaster.com/param/asp/psearch.asp?FAM=selfdrill&desc=Self%2DDrilling+Screws

Here are "sheet metal screws": http://www.mcmaster.com/param/asp/psearch.asp?FAM=selfdrill&desc=Self%2DDrilling+Screws

I would not like to see either one of the above used to terminate an EGC, but if I was an inspector, I would have no grounds to turn down the self drilling screws. The code needs to be changed to require the use of a machine screw or a machine bolt to make the section clear and enforceable.
Don(resqcapt19)

My picture of a self drilling screw.
It looks very much so like a mach. bolt, but the bottom of the bolt does not drill. A pilot hole must first be drilled,(smaller than the bolt) then the mach bolt is inserted into the hole when at the same time it acts like a tap. The bottom looks like a tap, but only about 1/2" up. The threads it makes will accept any normal mach. bolt of the same thread.

[This message has been edited by aphares (edited 12-20-2001).]

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[This message has been edited by Joe Tedesco (edited 12-24-2001).]

Joe,
Your last picture is what most in the trade would call a sheet metal screw. I agree that the code should require a machine screw or bolt, or other listed connection.
I don't see the inspector as having any choice. The code clearly only says you can't use sheet metal screws. This makes, by default, all other types of screws acceptable for grounding. This is one of the problems when the code is written to prohibit something as opposed to being written to requires something.
happy holidays
Don(resqcapt19)

Don:

This is a good reason to develop a Proposal for the 2005 NEC.



[This message has been edited by Joe Tedesco (edited 12-24-2001).]

Guys,
Lord knows I hate to get in on a good argument, but don't forget the BOCA, and standard engineering practices, would probably appreciate some mention of NOT removing the oxidation coating on a connection. A tapped hole, it is not necessary to remove the paint (or coating) to achieve a proper ground, and BOCA appreciates our not beginning a 'rust' hole because we find it convenient. Just thought I would mention that so your proposal could take that into account BEFORE we step on toes.

I need to elaborate the definition that I am trying to form, detween a self tapping screw, and a self tapping dolt. A self tapping bolt makes the same npn thread that a tap would. I would not use the screws you are showing in your pictures, because the threads are not npn. I believe the intent of the NEC was that, over time "IF" the screw was to become loose, or in need of repair than this same bolt could be refastened (torqued) or replaced, and done so without damage to the metal. Knowing my intent would you pass this version of a self tapping bolt ?
Look at the threads of the green screws suppled by the manufactures of most diconnects. there are two versions out, one is a mach bolt, that the hole supples it's threads, the other is npn threads that is tappered to go into the suppled hole that has no threads, it uses only the threads that it makes.
George Corron : (2002 NEC) "250.12"

Take one of the 8-32's out of a 4S, etc.metal box.
This is the screw that's a self-tapping.
It's OK. TEKscrews are sheet metal screws.
It's simple, don't split hairs.

After looking closer at 250.8, I can't permit any screws or bolts to be used to connect grounding conductors, except maybe the green 10-32 screws used in small enclosures. The section clearly requires the use of listed means to make the connection. I don't know of any screws or bolts, with the exception of the green 10-32 screws, that are listed for grounding connections. If I have a compression lug with a 3/8" hole on my grounding conductor, how can I connect it to the enclosure or building steel or other metallic object and be in compliance with 250.8?
Don(resqcapt19)

Guess I've been lucky in a way, I've been on heavy industrial (or similar) for a long time, Don, use Cadwelds, that's just about all I've seen in the last 10 years anyway, they're cheaper than you think, and reusable.

I believe your reading into that article more than what you should. I think the intent covers more "the Clamping of the conductor." and they didn't hit much on the way you would mount the clamp, Other than restrict the use of one kind of screw, and allow all others.

The substantiation for proposal 5-306 in the 1995 Report on Proposals that resulted in the "sheet metal" wording being placed in to the code indicated that this rule applies to both the direct connection of a grounding conductor as well as to the connection of a lug on a grounding conductor to the enclosure.
Don(resqcapt19)

Many fans, light fixtures, etc. come with a self tapping 8-32 screw to connect the ground.
Don, I think you might have gone a little bit overboard in your interpretation. (besides, you don't "permit" anyone to do anything other than your own work unless you're an AHJ)

Just to throw another fly into the ointment, most if not all mounting methods for EGC terminal bars use a set of self-tapping screws that tap into pre-punched holes in the panelboard cabinet back. So are some here saying that this technically isn't NEC compliant?

The difference between self-drilling, self-tapping, and plain ol' sheet metal screws seem pretty clear, in both definition and the graphics above. There are numerous places where the Code seems to expect us to use logical reasoning beyond the written portion of the Code

Dallas

[This message has been edited by Dallas (edited 12-23-2001).]

electure,
I was speaking in reference to my earlier post that said "if I was an inspector...".
As far as the interpretation, I am looking at the words in the code as well as the comments in the ROP and ROC. The CMP has "screwed up" here. The words used say we can only use listed means and therefore standard screws are a violation. This section needs a revision to make it enforceable. The sheet metal wording was never needed in 250.8 as sheet metal screws are not a listed means of connection. I will be submitting a proposal for the 05 code.
Don(resqcapt19)

Agreed, Don.
The Code should have been written in a more positive manner, rather than excluding anything as generic as a sheet metal screw. Any screw that is screwed into sheet metal could be construed as a sheet metal screw.

I think, though that if an inspector called me on having a good, solid machine screw used as a ground, and wouldn't let me off with 90.4, I would be inclined to whip out my box of crummy Ground Clips, show him the little UL stamp on each one, and exclaim "How do you like me now?" I think this would make an inferior connection as opposed to the first one.
I see on a daily basis Tek screws, toggle bolts, plastic anchors, drywall screws, and the like with ground wires shoved under them. I think the Code's intent is to provide a solid termination that won't come loose, and is used solely for the purpose of grounding.