A friend just had a 160 x 60 metal building for collector cars put up.
I noticed that the new 200 amp panel has the bare ground wire going through a hole in the metal siding to the ground rod outside but the building is not grounded.
There are no SE cables from the pole to the mast head or no wiring at all inside yet so the job is not finished but I told him that I think the building should be grounded, however I’m not sure about the ground wire size or how it should be attached.
I’m thinking that the contractor might not be a licensed electricion but not sure yet.
All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are present at
each building or structure served shall be bonded together to form the grounding
electrode system. Where none of these grounding electrodes exist, one or more of the
grounding electrodes specified in 250.52(A)(4) through (A)(7) shall be installed and
used.
Section 250.50 introduces the important concept of a ``grounding electrode system,’’ in
which all electrodes are bonded together, as illustrated in Exhibit 250.21. Rather than
total reliance on a single grounding electrode to perform its function over the life of the
electrical installation, the *NEC *encourages the formation of a system of electrodes
``that are present at each building or structure served.’’ There is no doubt that building a
system of electrodes adds a level of reliability and helps ensure system performance
over a long period of time.
This section was revised for the 2005 *Code *to clearly require the inclusion of a
concrete-encased electrode, described in 250.52(A)(3), in the grounding electrode
system for buildings or structures having a concrete footing or foundation with not less
than 20 ft of surface area in direct contact with the earth. This requirement applies to
all buildings and structures with a foundation and/or footing having 20 ft or more of 1/2 in. or greater electrically conductive reinforcing steel or 20 ft or more of bare copper
not smaller than 4 AWG. However, an exception does exempt existing buildings and
structures where access to the concrete-encased electrode would involve some type of
demolition or similar activity that would disturb the existing construction. Because the
installation of the footings and foundation is one of the first elements of a construction
project and in most cases has long been completed by the time the electric service is
installed, this revised text necessitates an awareness and coordinated effort on the part
of designers and the construction trades in making sure that the concrete-encased
electrode is incorporated into the grounding electrode system.
Exhibit 250.21 A grounding electrode system that uses the metal frame of a
building, a ground ring, a concrete-encased electrode, a metal underground water pipe, and a ground rod. Figured I would give you this info as well to assist you…again all depends on the construction and if that structual metal is an electrode by nature of its install, and the previous post deals with if it is to a building as a feeder or branch circuit…so it should cover most of it for ya.
Note: guess i am bias…I believe BONDING metal framing, structual framing and so on is VERY important so when someone says…it is not an electrode because it is not physically connected to an existing electrode…I want to bond it for safety reasons…just remember grounding is one thing…bonding to the metal is another…
You know what I find interesting about this topic is this…mind you I am venturing off topic a bit…kinda…
I see the 2005 requirement that if the “concrete encased electrode” is in place it is considered present…but if they install a vapor barrier down between the earth and slab is it present?
Actually the rebar used for the “UFER” should be in the footer and normally footers are in direct contact with the earth and well would be indeed the “CEE”…and if present you must connect to it ( in new construction )
Now…if the a building has structual metal…and simply bolted to the concrete floor…and no direct “not intentionally grounded” because it is not really a “present” electrode unless it meets 250.52(A)(2)…and not exposed let say…then do you need to connect to it…for grounding sake…I see Joe T is back on…whats your thoughts on it Joe…
Now if you mount the panel itself on the structual steel…and take the GEC out to the ground rods and it meets the requirements of 250.52(A)(2) then it is indeed part of the grounding electrode system…and bonding already takes place.
Thanks, I apologize for asking a question that I should know but that’s the sort of thing that sometimes happens when you reach the age of 70. :sad:
In fact, that’s the main reason I retired five years ago.
I didn’t find reference in my NEC 2005 NFPA code book but I’m sure I scanned right over it.
I intended to post more but the wife was over my shoulder, after me to get off the computer and do something so I kinda typed in haste.
It’s an all metal pre fab steel stand alone structure that came as a BIG giant erector set on two flat bed semi trailers, Butler building or something like that I believe.
First of all the first crew had never assembled one before and didn’t put in the big bolts that bolt it down to the footings, then had to jack hammer the concrete and epoxy them in later.
The footings were poured, then the concrete floor before someone noticed the bolts were left over.
That makes me wonder if they were smart enough to use rebar before they got fired off the job but I wouldn’t really be surprised if they didn’t and I’m sure they didn’t do anything at all pertaining to any electrical. (I didn’t see any rebar or scraps of any laying around)
The water service line and the gas service lines are both plastic and I’m sure there are no grounds other than the one ground rod that the “electrician” drove down.
There are going to be four metal storage containers (like a tractor trailer without wheels) placed out back within 8" of the structure or closer and I don’t think they will have any electrical but who knows, maybe lights some time in the future.
The service panel is mounted on a piece of 3/4" plywood so there is no connection between panel and structure.
Usually inspectors will call the building “bonded to the EGC of the circuit most likely to energize” if you use metal boxes screwed to the metal framing. That was how the Florida building code resolved the metal stud problem. If you put one metal box on each isolated section of metal studding they consider it bonded.
Agreed on that greg…but generally the metal inside framing is remiss from the structual metal bonding requirements…in fact in metal studs really dont get anything but your method is what i always suggest…but as with my many cryptic posts prir to this…they need to read them all and understand the difference in the grounding and bonding requirement. In Bristol VA tonight getting ready for a seminar tomorrow…i will break it down more tomorrow when i get a break…
Florida added bonding steel studs to the building code in the 2006 “glitch” session after someone died. (unbonded steel studs energized the medicine cabinet from an errant drywall screw) They did not amend the electrical code which is straight NEC 2005. They also did the same thing with the bonding grid under pavers. They picked up the NEC2008 “single #8” rule and put it in the pool section of the building code.
When I was inspecting I used the “EGC of circuit likely to energize” concept on any metal that wasn’t specifically addressed in 250. Usually securely attaching a bonded metal box will do it.
greg…is florida going to adopt the new section on AFCI’s…you had said they may ignore the 2008…i would think that is a mistake by Florida if they did…your thoughts
I think the AFCI and shuttered outlets may have prompted the “skip” of the 2008. I think the code folks just want the dust to settle a bit before they jump in. There is a concern that there will be a backlash from seniors about this receptacle thing. They already have problems with dissatisfaction on the AFCIs in bedrooms
not sure why they would be overly concerned on the AFCI’s …as of Jan 1…they finally get their protection for cords…lol…you know they finally openly solved that issue…until they find out the 5 A is too low as the new AFCI threshold …is it the added cost they are upset about?
AFCIs got a terrible reputation for the “fan” problem around here. I really believe it was just an installation problem, too much wire sticking out of that cludge neutral wirenut but the stigma still prevails. (even among electricians who should know better). I bet you could get more than half the guys at an IBEW meeting to say it is normal for refrigerators and washing machines to trip GFCIs (and by extension AFCIs). That is what they say about fans too.
A couple days of being late to work because the bedroom fan tripped the AFCI and your clock stopped and you have guys down at the Home Depot buying a $4 breaker. When my wife was running warranty calls on 100 homes, tripped AFCIs was a weekly occurance.
As for the tamper proof receptacle, it even says in the ROP that they have concerns about seniors being able to get the plugs in. We have lots of seniors here. Personally I don’t even see these as being that much of a safety enhancement. It may keep the dumbest kid out for a little while, but it just becomes a puzzle for the inquizative. I think your average 5 year old would figure it out pretty quick if they put their mind to it.
Two prong double insulated Drills always seem to have the prong bent just a little.
Then my language seems to make the plug just a little more receptive to the cord plug.
