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Joined: Oct 2006
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There's a community up this way called "Sterling" that was a joint venture between GE and United States Steel, built in the early-mid 1960s. This planned community was meant to showcase new building technologies that would result in affordable housing. Of course, the proximity to a huge international airport flight path affected the low price tags as well.
Anyway, just about anything that could be made out of steel in these houses was just that. Steel studs, trusses, doors, siding, pretty much everything but the sheetrock. They ran a #6 aluminum wire from the panel to a lug that was screwed into the siding with a #12 sheet metal screw. These all-electric houses featured GE brand 150 amp split bus panels, plus the furnaces, water heaters and appliances. There were bonding jumpers all over these houses to tie significant parts of the structure together. I'll never understand how this actually saved any money with all of that labor.
Today, these homes are maintenance nightmares since they didn't plan on the temperature extremes between inside and out. Moisture inside the walls eventually rusted the studs and caused major mold issues.
Sorry for the side track....
---Ed---
"But the guy at Home Depot said it would work."
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Joined: Mar 2005
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Large sheets of unbonded metal are just begging for a lightning strike. I highly recommend bonding for that reason alone.
I recommend bonding for safety, as well. This metal is just as "likely to become energized" as structural steel is.
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Joined: Jan 2005
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Structural steel is not, generally speaking, considered 'likely to become energized.' You don't have to bond even the largest I-beam.
If there is an appliance that might fail, and energize the steel, that is a different situation, and the bonding is accomplished at the appliance.
The only bonding issue regarding structural steel is where that steel is going to be used as the grounding electrode - for, say, a transformer. I would certainly hope no one is using sheet metal as the ground when they 'create a neutral' at a transformer!
In nearly every other circumstance, the incidental bonding that comes about in the course of normal construction is perfectly adequate; there is no need for bonding lugs or jumpers.
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Joined: Mar 2003
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2008 NEC 250.104 (C) Exposed Structural metal that is interconnected to form a metal building frame and is not intentally grounded and is likely to become engerized Shall be bonded to the Service equipment encloser at the Service.
Also see 250.104 (D) 2.
250.30 (A)6.
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Joined: Jan 2005
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Right ...we're right back where we started ... "likely to become energized' is NOT the same as 'gee, if I try hard enough, and enough things break, it might become energized.'
As for 'bonding.' simply screwing the panel to a column accomplishes that.
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Joined: Mar 2003
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So we"re depending on the Screw supporting the Panel to bond the steel???
250.8 List Permitted Methods for grounding & bonding. I don't see Panel screws on there??
Even the service must be Bonded to the Structureal steel .
2008 Handbook page 241 Right after 250.104 (C) Explaination:
250.104(C) Requires exposed metal building framing work that is NOT intentionally OR inherently grounded to be Bonded to the service equipment or grounding Electroid syastem . This requirement applies to ALL metal framework not only to steel framework.
Last edited by Yoopersup; 11/10/09 06:54 PM.
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Joined: Jan 2005
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I'm not sure I see your objection.
250.8 mentions screws as acceptable in two forms, and the panel itself comes with a green screw for bonding the case. Ground busses attach with screws. 250.8 also mentions 'assemblies.' So, where's the problem with the panel mounting screws?
Ah, maybe you're thinking of the 'no other purpose' regarding jumpers in junction boxes. OK, the top two mounting screws are for mounting; that third one is my bond. Voila!
Perhaps you would prefer to see a little green wire poking out of the panel, then attaching it to the column with ... you guessed it ... a screw?
Well, we could weld the things together ... except that would compromise the strength of the column. Incidentally ... aren't all those bits of structural steel held together by ... screws?
As far as bonding the service, that is an entirely different matter, and is more an instance of 'deliberately energizing' than 'likely to become energized.' We're using the structure - or more correctly, it's anchors - as a grounding electrode. (Which is why we use it for grounding transformers).
Let's face it; if we were expected to bond the structural steel, we would be allowed to use it as an equipment grounding conductor. Yet, we are forbidden to do so.
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Joined: Jul 2004
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Reno, your thinking may have been acceptable in 1968 but the current thinking at NFPA is if it could possibly happen, in anyone's wildest imagination we better invent a product and write a rule about it.
Greg Fretwell
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Joined: Mar 2003
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I've seen Metal roofing, Trailer skins, & Pole building metal engerized . So it can & does happen/
Another example they add on to a block building with structal steel and block BUT the two sections of building Old & new (steel) are not tied togerther. Thus one sided bonded other is not expect by conduits & mechical pipes. I;d say Bonding jumpers between the two seperate steel sections is required . Otherwise your depending on conduits ect to bond your steel,
Last edited by Yoopersup; 11/10/09 07:35 PM.
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Joined: Nov 2007
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Please, please, please ... don't open that can of worms, KJ!
Alright, but what else are we going to talk about?  ... how many pieces of NM we can fit into a two-screw connector. 
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