trough/wireway bonding
- Thread starter c_picard
- Start date
- Status
- Location
- New Jersey
- Occupation
- Journeyman Electrician
If it's a metallic raceway the locknut can be used to bond the wireway unless we're talking about a wireway with service conductors.
To make for a cleaner looking install, we use a 4x4x36" trough under our PV inverter and related components, with EMT up to each. Engineers will definately not be OK with just using the locknuts, they actually call out bonding bushings all around (PITA)! Anyhow, I like to put a seven hole ground bar in the trough and send a EGC through each conduit, and it's quick and easy to tap a hole or two for the mounting screws. I'm being advised that this should be through bolted because I can't guarantee three threads of contact? If that's the case how are all these 4 square boxes out there bonded?
Anything to make things more complicated I suppose?!
Anything to make things more complicated I suppose?!
- Location
- Massachusetts
NEC wise just the locknuts would be fine and a 10/32 tap hole would be as well.
That said the EE inspectors in MA for the credits can be hard to please. In one case I had to wait for three different EEs to battle out a compliance issue and they wrote a 'ruling' that basically said I was in a position where I could not comply with all the rules and they would accept what I did. (It had to do with aluminum panel frames, stainless hardware with tin plated copper lugs. :roll
That said the EE inspectors in MA for the credits can be hard to please. In one case I had to wait for three different EEs to battle out a compliance issue and they wrote a 'ruling' that basically said I was in a position where I could not comply with all the rules and they would accept what I did. (It had to do with aluminum panel frames, stainless hardware with tin plated copper lugs. :roll
I hear ya Iwire, don't even get me started on the Weeb vs. lay-in debate!
Have you ever heard of any substance behind the "three threads engaged" argument? Is that a UL guideline?
I kinda feel that the copper EGC's are above and beyond as it is, and surely atapped hole makes a robust ground path...
Anyhow, at the end of the day I have to do what the Master says, sometimes frustrating though, because when asked what's taking so long the answer always sounds like whining.
Have you ever heard of any substance behind the "three threads engaged" argument? Is that a UL guideline?
I kinda feel that the copper EGC's are above and beyond as it is, and surely atapped hole makes a robust ground path...
Anyhow, at the end of the day I have to do what the Master says, sometimes frustrating though, because when asked what's taking so long the answer always sounds like whining.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Two threads engaged, 250.8(A)5 and 6.
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
Since the screws most likely stick out the back anyhow, why don't you just put a nut on them? Now they're through bolted too!
because I just drill a hole in the back of the trough, into the sheetrock or plywood behind and thread the hole with my triple tap. To add the nut (one more thing to find a spot on the van for) now I have to make a hole in the wall where the nut lands so the trough sits flat to the wall. Or mount to the bottom of the trough, now I need a stubbly flat head to tighten the terminal screws. (those terminals have a torque spec, right? How do I get my torque driver in there?)
Was quick and code compliant, now slightly less so.
The screws that come with the ground bar are 8/32, are enclosures a minimum thickness to get their listing?
1/8" = 2 threads, no?
Was quick and code compliant, now slightly less so.
The screws that come with the ground bar are 8/32, are enclosures a minimum thickness to get their listing?
1/8" = 2 threads, no?
No,...1/16" = 2 threads
kwired
Electron manager
- Location
- NE Nebraska
If your wireway is at least 1/16" thick (it likely is) you comply with NEC with 32 pitch screws.
Have you tried Greenlee's drill/tap (don't know what the actual name is) bits? They have a drill tip and tap all on same bit, and 1/4 hex shank that fits quick change or extension adapters, which also is very handy at times. Saves a lot of time vs drilling, then tapping.
Oops, I intended to write 1/8" > 2 threads...
Yeah, that Greenlee bit looks sweet. I wonder if the powers that be are cross contaminated by an argument made by J. Wiles et al against lay-in lugs and self-threading screws on PV module frames. Seems like pressure resulting from an article or two that he wrote on the subject resulted in manufacturers suggesting a backing nut in their instructions. PV module frames are typically thick enough to have two threads engaged, but the "manufacturer's instructions" thing trumps the NEC as far as the ahj is concerned.
I like to use a more common sense view...Is a metal trough with EMT, locknuts, EGCs in every pipe, bonding bushings, and a ground bar field installed by a licensed electrician effectively grounded? Will it provide a reliable and robust path for fault current? I would hope so. And sometimes common sense aligns quite well with code compliant, and I believe this is the case in this instance.
Yeah, that Greenlee bit looks sweet. I wonder if the powers that be are cross contaminated by an argument made by J. Wiles et al against lay-in lugs and self-threading screws on PV module frames. Seems like pressure resulting from an article or two that he wrote on the subject resulted in manufacturers suggesting a backing nut in their instructions. PV module frames are typically thick enough to have two threads engaged, but the "manufacturer's instructions" thing trumps the NEC as far as the ahj is concerned.
I like to use a more common sense view...Is a metal trough with EMT, locknuts, EGCs in every pipe, bonding bushings, and a ground bar field installed by a licensed electrician effectively grounded? Will it provide a reliable and robust path for fault current? I would hope so. And sometimes common sense aligns quite well with code compliant, and I believe this is the case in this instance.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
IMO you could stop at locknuts. The rest of the stuff isn't required.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
You're not wrong because you want to exceed the code requirement. Many times that will result in a higher quality job. After all the NEC is considered a minimum safety standard.
While you were sleeping....we here in the states aren't exactly engaged in a struggle to exceed current quality standards. On a day to day basis I feel enormous pressure to produce more with less. I try my best to not compromise safety, but I sure don't get any points for overbuilding. I can't use 14" tie wraps because using 11's saves the company 50k a year. This is sort of the backround to my original post, tapping a hole is effective, redundant in this application, quick and compliant. Requiring a few more seconds in this part of the job means I need to balance my job budget by shaving a few seconds somewhere else...maybe in an area where safety or quality is actually compromised.
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