Ok, this is not a joke. A contractor called me and told me an inspector in a neighboring jurisdiction had told him EMT connector locknuts were no longer acceptable for grounding when using the conduit as an equipment ground. All locknuts have to be replaced with the grounding type locknut with the little screw. The inspector said he was told this at a seminar and no other info was forthcoming. I checked the UL info on EMT fittings and there were no restrictions. The KO's were cut accurately and there were no concentric or eccentric KO's. Voltage was 480. Anybody heard of anything regarding this?
Simularly, but not for Equipment Ground, around here SF, CA we must use grounding type lock-nuts, or ground bushiings on conduits for electrode, and bonding conductors. I don't see a problem for EG's.
But with 277/480, they want Ground bushings, or Ground lock-nuts on all concentric, and eccentric KO's. Something I dont see a point in.
250.97 Bonding for Over 250 Volts. For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (1). Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed for the purpose, the following methods shall be permitted: (a) Threadless couplings and connectors for cables with metal sheaths (b) Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets (c) Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets (d) Listed fittings that are identified for the purpose Bonding around prepunched concentric or eccentric knockouts is not required if the enclosure containing the knockouts has been tested and is listed as suitable for bonding. The methods in (a), (b), and (c) of the exception to 250.97 are permitted for circuits over 250 volts to ground only where there are no oversize, concentric, or eccentric knockouts. Note that method (c) permits fittings, such as EMT connectors, cable connectors, and similar fittings with shoulders that seat firmly against the metal of a box or cabinet, to be installed with only one locknut on the inside of the box.
[This message has been edited by e57 (edited 11-17-2004).]
Mark Heller "Well - I oughta....." -Jackie Gleason
Re: EMT locknuts for Grounding#44984 11/17/0409:05 AM11/17/0409:05 AM
Either I have had the same inspector, or they both attended the same seminar. I couldn't believe what I was hearing, and when I laughed and told him he was crazy, it did not endear me to him much.
Soare's Book on Grounding (8th Edition, pp129) has a report on a test conducted on conduit fittings and locknuts. "Conduit Fitting Ground-Fault Current Withstand Capability" , issued by UL, 6/1/1992 In a nutshell,[my paraphrasing] of Over 300 assemblies tested, from 10 manufacturers, 7 were deemed as insufficient. Yes, 6 were EMT fittings with zinc die cast locknuts without serrations installed on painted surfaces. (an example of the test, 3/4" fittings were subjected to 1530 amps for a 6 second period).
The conclusion made-- "5. As a result of the tests, it was observed that if the fitting provides good electrical contact to both the enclosure and the conduit, the fitting will provide a suitable equipment path for fault current."
Good enough for me unless it's been superceded
My Mickey Mouse inspector wanted grounding locknuts, bonding bushings, or Myers hubs for all the EMT fittings. He wouldn't write it up when I asked him to. I just made sure that there was no paint under the locknuts, and left it. I think the TI electrical contractor told me that he wanted them on the 4-S boxes, too. He also wouldn't final the building shell because I had a bad light bulb.
I think he needs to get his money back for the seminar.
PS, sandsnow, I do mostly service & warranty, & small TI's. We've not been "formally introduced". My last trip into your town was to advise the girls at your new Chamber of Commerce office (our company did the work) to just leave the occ sensors alone. They were trying to use them like the wall switches in their homes, with "frustrating" results (& I know some old AJS guys)
[This message has been edited by electure (edited 11-17-2004).]
Re: EMT locknuts for Grounding#44985 11/17/0410:52 AM11/17/0410:52 AM
electure AJS, now that brings back memories. I still see guys from there. Anyway, what you posted from the Soare's Book was just what I needed. I suspected something like that. He only heard half of the story.
My conclusion to the test is then to make sure the locknut cuts through the paint. I need to read that portion of the Soare's Book first.
Larry LeVoir Inspector City of Irvine, CA
Re: EMT locknuts for Grounding#44986 11/18/0402:07 AM11/18/0402:07 AM
The inspector Electure is talking about made us run ground wires in ALL EMT conduits. I had 7' lengths of EMT running from 4s bracket boxes for switches to a J-Box in the ceiling. All of them needed grounds with bonds to the back of the box. Also, I fully tightened down all set screws and used a hammer and a screw driver on all lock nuts. So it wasn't an issue of a poor install.
I wonder what he is going to say when the 2002 NEC is adopted here in Cali with the new addition explicitly adding EMT as a EGC.
2002 NEC 358.60 Grounding. EMT shall be permitted as an equipment grounding conductor.
Re: EMT locknuts for Grounding#44987 11/18/0404:01 AM11/18/0404:01 AM
Oh did you not know.... the "hammering a screw driver on the locknut is not an acceptable method. The Code says wrenchtight, not hammered with a screwdiver tight."
I was told that by an Inspector once, and luckily I had a little pair of Knipex channel locks on me... So I could make the lock-nuts "wrenchtight".
He nearly quoted a something I saw on an add for Klien "lock-nut pliers" something about to conform to the NEC all lock-nuts must be "wrenchtight", So now Klien makes the handy dandy not available anymore pliers, specificaly for the purpose.
Do you think I own a pair of "lock nut pliers"? NO!
I hammer them with a screwdriver (The Beater), and a pair of linemans, like everyone else.
Mark Heller "Well - I oughta....." -Jackie Gleason
Re: EMT locknuts for Grounding#44988 11/18/0405:48 AM11/18/0405:48 AM