Isolated Structural Steel
- Thread starter augie47
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I don't know. Art. 250.104 (C) talks of structural metal but it also states "to form a metal building frame" so I think not unless I am missing something. Of course any metal boxes will ground the ceiling via the egc but...
In my opinion, 250.104(C) can be interpreted to mean any portion of a building's framework that is metal. That is, the metal framework does not have to constitute the entire framework of the building (or structure, for that matter).
Hendrix
Senior Member
- Location
- New England
Many plans require that.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I would surely hate to bond every truss together in the entire building.
Don't they usually have metal braces between them anyway?
If we need to bond metal piping why not the roof trusses, there is typically wiring installed there - I myself do believe that it is usually inherently bonded by the wiring methods and equipment attached to it but this is not always good enough for metal piping systems either.
RICK NAPIER
Senior Member
- Location
- New Jersey
A metal truss ceiling IMO would fall under 250-104.
- Location
- Illinois
- Occupation
- retired electrician
250.104(C) requires exposed structural metal to be bonded if it is "likely" to become energized. It is a rare case where the exposed structural metal is likely to become energized. If we were still operation under the old code wording that required bonding where the metal "may" become energized, I would say that all of the metal would have to be bonded, but I don't see that as the case with the current code wording.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
...and this subsection does not have the same allowance as in 250.104(B)
"The equipment grounding conductor fro the circuit that is liekly to energize the piping shall be permitted to serve as the bonding means."
Don
Would you say the steel would be 'likely to become energized' if there was a junction box with conductors that is supported to the steel?
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Again what does likely mean. Think about the number of JB's out there and then think about how likely the steel is to become energized from the cable. Generally a short is made in a box or at some termination not because it is attached to metal.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Standard trusses stand alone, not sure about metal trusses.
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Dennis
Do you think the fault condition you mention could ever be transposed onto the steel the box is mounted to?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Of course it can but is it likely to- IMO, No. This is the problem with the "term likely to".
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
That is the key to this whole issue. It may not be to you, but what about some inspectors. Who is to say which person is correct?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
That is why I said the term stinks-- it leaves too much to subjectivity. Here is my thinking, if they wanted all the steel bonded then they should say that-- it leaves too much room for argument but of course, my ruling is the correct one. :grin:
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
- Location
- Illinois
- Occupation
- retired electrician
Short of bare (uninsulated) conductors being run on insulators on the steel (and I am not even sure that this type of installation would be "likely" to energize the steel) I can't really think of any code compliant installation where I would say the steel is likely to become energized.
Note: It is CMP 5's position that the terms "may become energized" and "likely to become energize" mean exactly the same thing. I just don't agree and maintian that there is a substantial difference between the two terms.
Likely to Become Energized is defined but it is obscure ...
Likely to Become Energized is defined but it is obscure ...
In a conversation I had a couple of years ago with Mr. Jeff Sargent, I noted that the term ?Likely to Become Energized? (which appears approximately 15 times in various NEC Articles) is undefined in the NEC, and it should be defined as it appears in multiple Articles and the term is ambiguous.
He informed me that the term is in fact defined in the 2003 (latest edition) NEC style manual (page 26) which defines ?Likely to Become Energized? as: ?Failure of Insulation on? ?
I believe our conversation ended on a note that with regard to this phrase within the NEC, one would have to ask: Over the lifetime of a given installation, is insulation failure likely and can that cause metallic objects to become energized?
? If so, proceed to Section 250.104 for compliance ?
I do hope this is helpful.
mweaver
Likely to Become Energized is defined but it is obscure ...
In a conversation I had a couple of years ago with Mr. Jeff Sargent, I noted that the term ?Likely to Become Energized? (which appears approximately 15 times in various NEC Articles) is undefined in the NEC, and it should be defined as it appears in multiple Articles and the term is ambiguous.
He informed me that the term is in fact defined in the 2003 (latest edition) NEC style manual (page 26) which defines ?Likely to Become Energized? as: ?Failure of Insulation on? ?
I believe our conversation ended on a note that with regard to this phrase within the NEC, one would have to ask: Over the lifetime of a given installation, is insulation failure likely and can that cause metallic objects to become energized?
? If so, proceed to Section 250.104 for compliance ?
I do hope this is helpful.
mweaver
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