Have 2 houses that are almost complete – side by side. Electrical trim outs this week. Today the electricians went though 14 ground rods trying to find a place where they could be driven into the “ground”. Do dice. Rock everywhere. I knew there was rock around there but DANG… Apparently there is about 12-24″ of cover soil and then just rock. Looks like maybe halfway between sandstone and granite… FYI – once they try to drive ’em and they start going into the rock, there is no getting them out… have to cut them off just below grade. They were using a demo hammer with a female ended bit that fits the ground rod to drive ’em. We are required two 8′ ground rods 6′ apart with the heavy copper conductor (maybe a #10?) connecting them to the service entrance/main panel….
What now? I’m between a rock and a hard place – pun intended. Called the rental place – he offered a 90# jack hammer with tow behind the truck compressor. Would that work? I’m thinking the rods would just bend. Plus, who is man enough to climb a ladder with a 90# pavement breaker and operate it???
Head electrician says I need to dig a trench 30″ deep for them to lay the ground rods in – kinda hard when the rock is only 12 – 24″ down….
Yea – I know – seeing ufer grounds crystal clear in hind sight…
EDIT: I meant to post this in the electrical folder….
Replies
what type of foundation???
time to rent a rock drill....
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Forget the primal scream, just ROAR!!!
These are slab houses. (barf) Rock drill with an 8' bit??? A quick google turned up this. Heavy equipment rental guy didn't say anythig about that or similar. I asked if he had anything to drill 8' into rock. Or, do you mean drilling rig - that was one thing I was thinking of.
Another option someone mentioned was to replace the PEX water service (city water) with copper - which could happen, but not all the way into the house since the "in house" end is under the slab foundation... The coper pipe would be at least about 20' from the service enterance...
that be the drill....
now all ya need is the bit and shank....
with all the rock around you the rental outfits must have solutions....
are you hitting indvidual rocks or are you on a rock shelf???
got a water laser handy???
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
Edited 5/23/2008 8:51 pm by IMERC
I don't know if it is individual rocks or shelf, but if it were individual rocks, it seems that with 14 tries they would have gotten one to go in... What's a water laser?
skid off the top layer of dirt for a liitle ways.....
you looking at end or flat grain in the rock???
really large indivduals???
end grain and you may find a seperation to work with...
flat and you get out the drill....
water laser or water laser jet...
this will give ya some ideas.....
size matter with on this deal....
http://www.teskolaser.com/waterjet_cutting.html
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
I should have taken a pic of the rock there on site... Here is a pic from another site of somewhat similar rock - it's not in layers. I guess it's not "ledge"? Notice the "teeth" marks in the closest rock. It's not real hard - but definitely hard enough. Don't let the fact that they appear to be individual rocks fool you. We are pretty sure these were blasted and then the developer's site work guy buried them.
plate... 1st choice...
trench.... 2nd choice....
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
That looks like a mineral layer we call calichie. Its hard but not that bad. It doesnt look that thick so you should be able to bore through . Or drive the rods at a 45 degree angle and add a couple of rods to give enough grounding area. Think about it. 2 rods driven into gravel satisfies code but whats the actual effectiveness of them. Local code in Lincoln Co. Ore. calls for Ufers .
PS - if you drill a hole in the rock to drive the rod, will it make the correct ground contact? Or, would it require some kind of different grounding rod, etc?
bedding the rod in the rock won't pass test...
unless ya cheat....
but later that comes back to haunt ya....
the hope is to bore thru the rock...
if you are on bedrock 2' down.. put a trench in with a rock cutter....
place yur #2 copper and bury...
if you are on shelf... bore thru....
any goodly sized trees near by???
why didn't somebody field the ground to the rebar in the slab...
I know... no rebar.....
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
I have no idea if this is code or not, but do these houses have basements? if so could you run the rods down under the basement floor, or does the rock extend down that deep?
No basements. Not doing any foundation work at this late stage in the game....
Edited 5/23/2008 8:26 pm ET by Matt
Trench it as deep as you can, then build up the top soil to make it 30".--------------------------------------------------------
Cheap Tools at MyToolbox.netSee some of my work at AWorkOfWood.com
when he trenches he may find a break in the rocks...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
All the better. I just home that break goes 6' down.--------------------------------------------------------
Cheap Tools at MyToolbox.netSee some of my work at AWorkOfWood.com
We're doing a house with minimal soil cover. If we had not done a Ufer ground then I would have had to rock-hammer a ditch, lay ground plates in, and cover with soil. You may have to do something similar. I would ask the inspector what s/he will accept.
Ground plates? Never seen 'em. Anyone know what NEC 2008 has to say about that???
I looked an NC is still on the 2005 NEC until June 1. And that should only affect NEW work.http://www.ncdoi.com/OSFM/Engineering/BCC/engineering_bcc_electrical_codes.aspI did find one amendment."AMENDMENT 250.50
Delete NEC 2005 text and replace with:250.50 Grounding Electrode System. If available on premises at each building or structure served, each item in 250.52(A)(1) through (A)(6) shall be bonded together to form the grounding electrode system. Where none of these electrodes are available, one or more of the electrodes specified in 250.52(A)(4) through (A)(7) shall be installed and used."Orignal"250.50 Grounding Electrode System.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.Exception: Concrete-encased electrodes of existing buildings or structures shall not be required to be part of the grounding electrode system where the steel reinforcing bars or rods are not accessible for use without disturbing the concrete."As far as I can figure out they are saying the samething. The NEC version has an except so that you don't have to open up a footing to make it a ufer ground. While the NC uses If Available On Premises to get the same exception.BTW I have no ideal about doing this. But how hard would it be to break out a small section, attach the ground electrode conductor and patch the footing/foundation and maintain structural integrity?BTW, what is the construction? Is this a slab with interal (monolithic) turned down footings?.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
>> BTW, what is the construction? Is this a slab with interal (monolithic) turned down footings? <<
yes.
Bill, have you seen this thread?
http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=104945.1
Sounds like if it keeps moisture from wicking into the walls, it must be waterproof enough to maybe not work for a UFER?
Joe H
Yes I saw that and wondered about a Ufer.Now the code says, if I interpret it correctly you don't have to install a ufer if the footing does not qualify.And the NEC is pushing more and more for mandatory use of ufers.But apparently, in many areas, the BI are completely ignoring it.So my guess is that you could use that and not have it a ufer, but if you are in an area that the AHJ are pushing for ufers then you need to have a reason for using it other than "it is easier".I did remember seeing some place where someone was doing a service upgrade and the AHJ was require adding a ufer to an existing building that was not part of the buidling foundation..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I will toss a few items out here from my experience with Ufers here in my part Ore. Our inspectors insist that one continuous 20' piece of 1/2" bar or larger be in the footing, Tied to that using standard tie wire we add the leg of at least 1/2" bar that is upturned to come above the stem wall at least 18". Lap must be 4' minimum in my location, can't say about other locations. Using one piece with an upturned bend and having less than 20' continuous in the footing doesn't cut it.
Bar in the footing may not be in direct contact with the dirt. Ground wire is clamped to the bar using an approved clamp.
Here our BI's have reached an agreement with the Electrical codes people that at the time of footing inspections the BI's check for the Ufer being installed and tag it as approved, no Electrical inspection needed then. This saves everyone time , money and hassles. Failing having the Ufer installed can be gotten around by using #4 copper wire encased in a concrete pour , minimum 20' long and buried a minimum of 24" in a separate trench, deeper is better but they will accept the 24". Wire must be continuous until it comes above the final foundation grade and must leave room or length for an approved clamp to be used, or any other NEC approved method. They have been the standard for at least 10 years here.
They can't get your Goat if you don't tell them where it is hidden.
Let me make sure I understand one point.... There is no copper in the concrete? Right? The copper and the clamp are above the concrete - right?
Matt, No , sorry bad sentence composition on my part. I meant a separate trench from the footing trenches. A trench is dug to the minimum depth , #4 wire is held 2" (IIRC) off the bottom of the trench with dobies or something similar and encased in concrete (Wire must must be help up off the ground and completely encased). Also their is a maximum distance from the building footing the UFER can be , 10' IIRC.
They can't get your Goat if you don't tell them where it is hidden.
We need some input from Art on this.
Way too many choices that just don't sound good.
rusty old rebar doesn't seem like a good conductor, just tie wired together doesn't sound like a connection I'd rely on to heat my toaster.
Joe H
JoeUfer came out of work to provide grounded for munitions buildings during WWII.http://www.psihq.com/iread/ufergrnd.htmhttp://www.scott-inc.com/html/ufer.htm.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Bill, I book marked for further perusal, but, one site says don't use the copper wire in concrete that NEC says to use.
The other one has his rebar bent down and protruding out of the concrete. that doesn't sound good either?
Seems like the best would be (if no copper in the concrete) a piece of rebar out the top with your connection there.
My next project is in another state so I'm not sure what they will want.
Joe H
Edited 5/25/2008 2:47 pm by JoeH
"The other one has his rebar bent down and protruding out of the concrete. that doesn't sound good either?"If you are talking about this one.http://www.scott-inc.com/html/ufer.htmI think that what is is saying the at the rebar in the slab turns donw into the footing.Look at the picture with the note that those protrude from the PAD and then the dashed line and the note FOOTER..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I questioned the use of tie wire when we were first told to use them instead of ground rods, answer was it works just fine. I am not a sparky so go with what the rules are.
They can't get your Goat if you don't tell them where it is hidden.
Are there any builders or sparky's here that work in or around El Paso?
If so, they'll have the answer. In that mesa, the bedrock is the ground surface.
Politics is the antithesis of problem solving.
could you use grounding plates instead of rods? I've seen them at home depot up here in canada. Don't know what the code says where you are but its worth a shot.
Look at NEC Art 250.52. Plate electrodes maybe your best bet at this point. Art 250.53 requires that they be installed at least 30 inches below surface.
Jackhammer or bit on a skidsteer will break up the rock usually. The code doesn't specify, but plates should be installed vertically to reach more soil moisture.
Jim
Again, havent seen plates before, but seems like they would make for a smaller hole to be made in the rock. Google brings up this. Electrician asked for two 8' trenches 30" deep and 6' apart. These are tight subdivision lots. Can't get much of anything big in there.
Plates must be at least 2 sq ft of surface and 1/4 inch thick if iron or steel. Steel shop can cut that for you. Have the copper ground wire welded or brazed to the plate along its length, not just one spot.
Telecom supply house will have these, they are usually with serrated edges for more surface area. Plated for longer life, also.
However, guessing that you are under a time crunch now, if you can't find a plate to buy, have one made and get the ground wire welded to it.
Concrete-encased electrode is out, can't get ground rods in, can't get ground ring in. Replacing PEX sounds too late, and the ground may be corrosive. Under Art 250.53 (G) you might be able to bury the rods horizontally (trench), but your inspector may still require a plate ground. They really want to see a Ufer ground now, and if you don't have that, then a plate ground. So as a practical matter, that's about the only option left.
Jim
Seems like he could dig a trench, install rebar or wire, and pour concrete over it.
What is wanted is not the will to believe, but the will to find out, which is the exact opposite. --Bertrand Russell
They won't let a grid be installed?
As I understand it, the grid would still need to be 30" deep.
I'm not sure if using a copper water line would be a good idea.....but not my expertise.
Could you have a well driller come out with his rig and punch two holes for you with his rig?John
J.R. Lazaro Builders, Inc.
Indianapolis, In.
Well driller...
Blasting companies have drilling rigs that drill rock all the time... I know of a few. Hello big time construction timeline delay....!!!
Delay? Maybe not. Sometimes those guys can squeeze in a quickie job like that. I would just have your utility locates ready and give them a call.John
J.R. Lazaro Builders, Inc.
Indianapolis, In.
I found out about the problem yesterday at 3:00 PM. I called in the utility locates at 4:00 PM.
Still, I don't know if drilled holes will give the proper continuity to the rod - have no idea...
Edited 5/24/2008 10:22 am ET by Matt
We are getting ready to do the driveway concrete (which now needs to be put on hold). I asked the head electrician if the UFER could be put in that. He said "No. The UFER must be in the house foundation." I hate going on here-say, but this guy is pretty knowledge. Like I said above though, I need to call the electrical inspector on Tuesday morning.
BTW - these are the houses that burned down. Nothing is known about how the fire started, except that it started somewhere in the garage of the one house. These houses have the electrical panel in the garage, with the meter base on the outside of the garage wall. I wonder if it was grounded properly.... I guess though if there was a lightning strike or something they would have known....
Matt,I had the same idea as DanH. (Glad I waited to post the idea, until I'd read through the other replies. LOL)Anyway...WHY is this unacceptable ? Why -MUST- it be in the house foundation ?Just because the electrician says so ? Just because that's the way they always do it ? Just because no one wants to buck the system ? Just because no one wants to take the time and trouble to research and see if this is just as good, or not ?Personally, I think it's a much better idea than the plates.You dig all the way to the rock.Two, 10 foot ditches.Lay in 5/8 or larger rebar. (Connect according to spec.)Pour 3 or 4 inches of concrete over the rebar. Fill the ditch back up.I think this is actually better than the house foundation. Something goes wrong with it, and it can be dug up and redone.It is definitely going to get enough ground moisture. Even if you raise the rebar a bit so it is encased in the concrete and will last a bit longer.
Politics: the blind insulting the blind.
Click here for access to the Woodshed Tavern
Dan H, can't just dig another trench, the UFER has to be at the bottom of the foundation, as already pointed out after your post.
The easy way is to run at least 20 feet of 4 AWG bare copper conductor or larger at or near the bottom of the foundation. Cannot have plastic sheeting at that area; the concrete must be in direct contact with the earth. The copper wire is brought up and out of the foundation to run directly to the main breaker panel (service entrance). Clamps are not allowed as the conductor exits the concrete. Grounds have to be welded or crimped with an irreversible crimp if something happens to break continuity.
The ground conductor may be clamped to the rebar.
The concrete will stay wet, and the underside of the concrete foundation wetter than the open soil, but it's the large surface area of the foundation that does the trick.
Without plating, the ground plate will last about 50 years or less. So if there is time to plan ahead, then a plated ground plate is better. Rods don't do that much better, except that they are steel rods plated with copper. Once the copper goes, then the rod goes altogether.
Jim
Electricians here found that by the time they came to do their rough in, the conductor was usually broken or compromised right where it exits the concrete. They now run it in conduit about three feet high and wrap enough wire to reach the panel around the pipe.
I haven't seen a rod or plate for years.
Edited 5/24/2008 7:20 pm ET by fingersandtoes
First of all why doesn't it have a UFER (concrete encased ground electrode)?
250.50
"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.
Exception: Concrete-encased electrodes of existing buildings or structures shall not be
required to be part of the grounding electrode system where the steel reinforcing bars or
rods are not accessible for use without disturbing the concrete."
And from the NEC handbook which is not code, but suplimental material.
"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."
So if it has footings then it should have a Ufer.
Here are the allowed ground electrodes from the 2005 NEC.
250.52
(1) Metal Underground Water Pipe - while you MUST use this if you have it, just adding it does not work. You still need a supplimental electrode.
(2) Metal Frame of the Building or Structure - NA
(3) Concrete-Encased Electrode An electrode encased by at least 50 mm (2 in.) of
concrete, located within and near the bottom of a concrete foundation or footing that is in
direct contact with the earth, consisting of at least 6.0 m (20 ft) of one or more bare or
zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of
not less than 13 mm ( 1/ 2 in.) in diameter, or consisting of at least 6.0 m (20 ft) of bare
copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be
bonded together by the usual steel tie wires or other effective means.
(4) Ground Ring A ground ring encircling the building or structure, in direct contact
with the earth, consisting of at least 6.0 m (20 ft) of bare copper conductor not smaller
than 2 AWG.
(5) Rod and Pipe Electrodes Rod and pipe electrodes shall not be less than 2.5 m (8 ft)
in length and shall consist of the following materials.
(a) Electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade
size 3/ 4) and, where of iron or steel, shall have the outer surface galvanized or
otherwise metal-coated for corrosion protection.
(b) Electrodes of rods of iron or steel shall be at least 15.87 mm ( 5/ 8 in.) in diameter.
Stainless steel rods less than 16 mm ( 5/ 8 in.) in diameter, nonferrous rods, or
their equivalent shall be listed and shall not be less than 13 mm ( 1/ 2 in.) in
diameter.
(6) Plate Electrodes Each plate electrode shall expose not less than 0.186 m 2 (2 ft 2) of
surface to exterior soil. Electrodes of iron or steel plates shall be at least 6.4 mm ( 1/ 4 in.)
in thickness. Electrodes of nonferrous metal shall be at least 1.5 mm (0.06 in.) in
thickness.
And here is more details of installations.
250.53
(F) Ground Ring The ground ring shall be buried at a depth below the earth's surface of
not less than 750 mm (30 in.).
(G) Rod and Pipe Electrodes The electrode shall be installed such that at least 2.44 m (8
ft) of length is in contact with the soil. It shall be driven to a depth of not less than 2.44 m
(8 ft) except that, where rock bottom is encountered, the electrode shall be driven at an
oblique angle not to exceed 45 degrees from the vertical or, where rock bottom is
encountered at an angle up to 45 degrees, the electrode shall be permitted to be buried in
a trench that is at least 750 mm (30 in.) deep. The upper end of the electrode shall be
flush with or below ground level unless the aboveground end and the grounding electrode
conductor attachment are protected against physical damage as specified in 250.10.
So it looks like which every option you take you need 30".
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Thanks for the actual citation from the NEC. At this point, I have to wait until Tuesday to talk to the electrical inspector to see what he says.
>> It shall be driven to a depth of not less than 2.44 m (8 ft) except that, where rock bottom is encountered, the electrode shall be driven at an oblique angle not to exceed 45 degrees from the vertical or, where rock bottom isencountered at an angle up to 45 degrees, the electrode shall be permitted to be buried in a trench that is at least 750 mm (30 in.) deep. The upper end of the electrode shall be flush with or below ground level unless the aboveground end and the grounding electrode conductor attachment are protected against physical damage as specified in 250.10. <<
I've seen them drive 'em an an angle and wondered about that.
Would you mind please showing us 250.10? Another Q I have is if we end up with the grounding mechanism say 15' from the house, how does the ground conductor need to be protected?
>> So it looks like which every option you take you need 30".<< Good summary point I needed to know.
>> First of all why doesn't it have a UFER (concrete encased ground electrode)? <<
UFER grounds are RARELY used here in in this part of NC in residential construction although apparently they are gaining popularity. We use ground rods. Now, I can see why, UFERs are gaining popularity. Personally, I've NEVER seen one and they aren't required by any of the 3 inspections dept jurisdictions I'm building in. A year or 2 ago, when I first read about them here I asked the head electrician of my electrical sub. My impression was that he had never heard of one, or at least wasn't very familiar with them. It is a large electrical company with approximately 60 trucks - to my knowledge, all they do is residential electrical and mostly new construction. Today, when I asked him again, he seemed more in tune with the idea of UFERs. Duh. We had maybe a 10 minute discussion and he didn't mention grounding plates. I'm thinking that UFERs aren't that popular because they add another inspection (and inspector) to the construction sequence which is a likely delay to the construction schedule. Obviously, in HINDSIGHT I wish we had delayed the construction of these homes another day for an additional inspection. The footers do have rebar in them. At that point in the game one of these customers were to the point of being rude (to me) about the progress of their home. They were very upset. The PE who engineered the plans had made mistakes requiring additional plan changes and a few weeks, but all the customer could see was that their time was being wasted. These mistakes were caught by me. It's difficult for people who don't actually work in the home building business to fully appreciate situations like this. Frankly though, the UFER ground never occurred to me at footer time - like I said - I've never seen one. OBVIOUSLY it will next time. I mean hey, I'm the superintendent and need to know everybody's job on the jobsite....
Edited 5/24/2008 8:10 am ET by Matt
" A year or 2 ago, when I first read about them here I asked the head electrician of my electrical sub. "I think that we had the discussion here.Dan does have a point.You could pour a "bump out" on the side of the footing. At least they are 3 or more feet deep."located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth," Now yours would not be a footing, but pass that by the inspector. I heard of one pass where they made someone do that on a remodel which is specifically not needed unless this is local amendment."250.10 Protection of Ground Clamps and Fittings
Ground clamps or other fittings shall be approved for general use without protection or
shall be protected from physical damage as indicated in (1) or (2) as follows:
(1) In installations where they are not likely to be damaged
(2) Where enclosed in metal, wood, or equivalent protective covering"300.5 covers underground wiring.And the default depth is 24".6" if in ridgid or imtermediate metallic conduit.4" if a under 4" concret slab and extends at least 6" on each side.18" in PVC conduit..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Bill:
One brief Q:
You said:
>> 300.5 covers underground wiring.
And the default depth is 24".
6" if in ridgid or imtermediate metallic conduit.
4" if a under 4" concret slab and extends at least 6" on each side.
18" in PVC conduit. <<
The word "imtermediate " I assume that is a typo and should be "intermediate"? What is intermediate metal conduit? Is that the kind they sell at HD and Lowes that can be bent fairly easily with one of those hand benders?
BTW: I get that the above is paraphrased, but are you actually hand typing all those code citations or do you have an electronic copy?
Thanks
I have an electronic copy.But the burial depth is in a table. And the table does no display correctly on my computer, much less trying to copy it."I assume that is a typo and should be "intermediate"" - YesThere are 3 type of metalic conduit. EMT (electrical metalic tubing)
Intermediate
RidgidEMT is the lightest weight stuff and what you use the armstrong bender for 1/2 and 3/4" at the home horror stores. All connections are by clamps."342.2 Definition
Intermediate Metal Conduit (IMC). A steel threadable raceway of circular cross
section designed for the physical protection and routing of conductors and cables and for
use as an equipment grounding conductor when installed with its integral or associated
coupling and appropriate fittings."And from the handbook."Intermediate metal conduit (IMC) is a thinner-walled rigid metal conduit that is
satisfactory for uses in all locations where rigid metal conduit (RMC) is permitted to
be used. Threaded fittings, couplings, connectors, and so on, are interchangeable
between IMC and RMC. Threadless fittings for IMC are suitable only for the type of
conduit indicated by the marking on the carton.""344.2 Definition
Rigid Metal Conduit (RMC). A threadable raceway of circular cross section designed
for the physical protection and routing of conductors and cables and for use as an
equipment grounding conductor when installed with its integral or associated coupling
and appropriate fittings. RMC is generally made of steel (ferrous) with protective
coatings or aluminum (nonferrous). Special use types are silicon bronze and stainless
steel."I believe that ridgid is the same wall thickness as common galvanized water pipe in the same size, but not sure.I have not had any need to work with either, but I think that risers on overhead service are ridgit and not intermediate.And you will find some of that at the borgs also. Because the weahter head uses a screw clamp you can get it threaded at one end and just cut to lenght in the field. There are also prethreaded elbows.So simple services can be done without any special tooling.But for someone trying to use that in an industrial setting then you need pipe threaders and hydraulic benders..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Thanks - so if I need to protect the #4 copper ground conductor that is only buried 6" going to a trenched in or otherwise somewhat remotely located ground electrode I need threaded conduit... or, go 18" deep with PVC or 24" with nothing... BTW - just for increased fun we are working in the area of the buried power service and gas lines... :-)
Yes.I think that your best bet is to trench next to the house and add a ufer "footing". While not technically a footing based on a couple of other comments apparantely that is common practice in some areas.I was just going to ask you how they got the electrical service in. Did they have to jack hammer a path?.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
>> I think that your best bet is to trench next to the house and add a ufer "footing". While not technically a footing based on a couple of other comments apparantely that is common practice in some areas. << Next to the house is only 5' on one house with a lived in house next door (10' away). The other has about 8' with a total of maybe 15' but I still can't damage the neighbors lawn, so getting a piece of heavy equipment in there isn't an option on at least one house. The utilitys hand dug on that one.
My plan for now is a) try to drive ground rods in the front yards (after it is located by the spray paint guys), and then, if that doesn't work, talk to the head electrical inspector about ground plates and the possibly of a new "footing" with a UFER ground wire in it. The footing could not be right next to the house though.
>> I was just going to ask you how they got the electrical service in. Did they have to jack hammer a path? << It's only about 18" deep (some less) and they put it in that grey PVC conduit. Remember that the utility's work is not inspected... except by themselves. The power company had some kind of "supervisor" over there... I don't remember what happened with the gas. Also, the rock problem is not so severe in the front yards. Only in the sides and backs. Utilities come from the street out front.
I'm going to site now to "supervise" the concrete guys a bit and explain to them what the problem is and why they have to hold off on a lot of their work.
My concrete guys would probably do any necessary hand digging for the right $$$ or I can get a guy in there with a track hoe or mini-excavator if necessary. Hand diggers can't deal with the 30 to 50 gallon trash can sized rocks that we have already pulled out of there... I'm sure there are bigger ones too.
You got a fix yet?.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I'm in the hurry up and wait mode. Without going through a long explanation, the Electrician and is guy were supposed to meet me at 08:00 this morning; with the distance, combined with something else I had to do first mandated I leave the house at 06:00. 08:30 I call him - he forgot... at least he didn't give me some BS story about a flat tire or something.
If they haven't produced in a few days, I'll need to go over there with an armload of rods and a sledge.... Trying to avoid that.
I know this isn't a very glorious ending but we were able to drive the rods in the front yards. (2 per house - 6' apart) On the one house we had to drive them at 45° to get them in all the way. I called the electrical inspector to verify that part was OK since the electrician said that some jurisdictions were no longer allowing that. He said we could use the ground plates if we really needed to.
We wasted another 3 rods on unsuccessful tries - not including the ones we (partially) drove and were able to pull out. So all together we had to cut off maybe 6 rods that wouldn't go in or out and another 4 got bent when I had a guy with a bob cat pull them.
On one house the first rod was about 15' from the meter base, and on the other it was about 20', so we had some fun trenching in some rock hard dirt... It was 94° today...
" so we had some fun trenching in some rock hard dirt... It was 94° today..."Better thee then me <G>..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Yea, well it went like this. Electrician said that the ground lead copper had to be 12" deep. I started on the one house - that was the one with ~26' of trench and the dirt was rock hard. That lasted about 10 minutes... Then I went over to the other house where the dirt was somewhat softer. The electrician and I dug that with a mattock (sp?) and trenching shovel that I was lucky to have in my truck. This took about 1/2 hour. This showed the young electricians helper (who was installing a few ceiling lights) that the old guys weren't lazy. Then we turned the young guy loose on the really hard stuff... After about 15 minutes of that I asked of the electrician had a spade bit for his rather large Bosch electric demo hammer we had used to drive the rods. He did and we used the demo hammer to fracture the hard pan, thus showing the youngin that the old guys were not only tough but smart... :-) The second trench took maybe a total of 40 minutes.... It was all good. Electrician is gonna bill me for the time and wasted ground rods...
I only skimmed through the replies, but the drill rig may be a legitimate option. About 10 years ago I was working for an environmental company and we were contracted by a crew putting in computers on telephone circuits in rural areas. They needed multiple ground rods in an area with shallow soil over sandstone, and we had a CME 45 drilling rig that could do a 4.5-inch hole ten feet deep in sandstone pretty quick (maybe 15-30 minutes per hole).
We drilled down about ten feet, they placed ground rod in a bentonite clay slurry (common for drillers to have this) and used a backhoe for the shallow trench to run ground wire between rods. The phone company had pretty strict requirements for the ground so we put in quite a few holes for rods at each site. The bentonite clay made a very good connection for the ground, but rock is generally not as good a conductor as soil.
Environmental drillers and geotechnical drillers tend to use the same general equipment. A structural engineer could make a recommendation to an outfit if they don't have their own rigs. They have a wide variety of equipment that could get most anywhere. Most are truck mount on the equivalent of a 550 or 650 chassis, but they are often track mounted, too, and it isn't too hard to find something smaller that will fit in tight spaces, though maybe take a few more minutes to drill the hole.
Depending where you are, I wouldn't worry too much about it slowing down the project. Drillers I work with are feeling the slump in the building economy and could schedule a small job like this pretty quickly - a ten foot hole with no soil sampling could be put in by any of their guys.
Good luck,-Nate
Each area has different interpretations of the same code. The one I just put in at the industrial site required it to be at least 6' from the foundation. It could be parallel or 90 degrees to it but must not be closer than 6'. The EE specked Copper not rebar and insisted it be maintained 2" off the ground in the bottom. Again he said deeper was better but the top of the concrete which was 8" thick must be below the frost line. Since I never had done this before I searched the Web for UFER grounds and found a lot of info. Seems the electric code people prefer these over ground rods. Also they will become standard replacing ground rods. Ware the rebar comes in is that the code will allow the rebar in a footing to be used as a ufer ground although Mr. Ufer likes Copper only. The correct way is to hold the rebar 2" off the ground in the bottom of the footing and be at least 20' long. The copper wire needs to be bonded to the rebar in the footing either by special clamps or cad welding. The connection will corrode if made outside the concrete.
http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=69078.15&search=y
.
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I had forgotten that discussion... I guess I didn't learn it the hard way... Now I have that experience. Great!
One thing I don't quite get about UFER grounds: So, I pour a footing with a piece of rebar sticking out to use later as a ground. Fine, but what is to keep that piece of rebar from becoming a rusty POS in 5 or 8 years that the ground clamp couldn't possibly have continuity to?
I am not sure about the detials of how it is/came be done.I know that there are clamps specified to be used in concrete. So one option is to connect the wire before pouring.But then you need to keep the wire protected and out of the way.I am not sure about this, but I think that you can bend the end of a rebar UP. And if you pour a slab over the footing (or if it is monolithic) so taht the rebar ends up in the wall. But clamp the wire to the rebar in the wll and put a cover plate over it for access.Now If you try something like that I would pass it by the inspectors first.There might be some other options..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Thanks again for your help on this issue. In the wall.... good idea. Hope the framers wouldn't cut it off to get it out of the way.... :-( Or, for a CS foundation, the bricklayers might decide it needs to be out of the way. Until this stuff becomes common practice I'm not sure this will really be a great solution. Next problem is that if it is covered with DW, then electrical inspector can't see ground at electrical final... so, access panel - more work & expense...
As far as the ground clamp in the concrete that is designed for that purpose with the appropriate copper conductor attached, now we are getting into the realm of an extra trip by the electrician.... They charge for that stuff...
That is a good pic. Is there another just showing a piece of rebar being bent up?
No and I don't know if that is appropriate or not. The NEC is not to be a design book, just a rule book. Although the handbook has some more material.I think that I have heard of bending the rebar up, but I am not sure that it is allowed or not.You might want to ask about this over at Mike Holt forums.You will get more experience people with more options..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
what is to keep that piece of rebar from becoming a rusty POS in 5 or 8 years
Been wondering that too. Doesn't a ground require a certain amount of ground moisture to work?
Those steel plates in the plate type system would eventually rust away to nothing. Maybe not tomorrow, but say 50 years.
Then what?
Seem like the 20; of 4 AWG in the foundation would be the most foolproof.
Joe H
What have others in the neighborhood done?
I thought about that, and kinda looked around today but didn't actually want to go walking through neighbor's yards, digging around in their landscaping, checking out their grounding. I'm thinking the other side of the street doesn't have an issue, based on the lay of the land. Even though the guys went through 14 rods today, I'm still not satisfied we can't drive some. One was driven out front for the T-pole which is only about 20' in front of one of the houses. The thing is that today, as they had trouble, they went closer and closer to the steep hill out back... Guess what's under the steep hill? I wasn't there when all this happened. Hindsight is always 20-20.
There must be a dozen acceptable alternatives to driving a ground rod, all helpfully detailed in the NEC. 14 tries? You need another electrician! At the very minimum, you need to chat with the local inspector, see what he'll accept.
There are only 7 methods of ground electrodes listed in the Code. If it doesn't meet code, then it won't pass inspection.
There are other methods to achieve grounding, but a method has to be presented with scientific evidence to the committee and the committee must vote to accept the new method and include it in the next code version.
Jim
"There are only 7 methods of ground electrodes listed in the Code. If it doesn't meet code, then it won't pass inspection."It is not that cut and dried.First the NEC is a worthless list of suggestions. What matters is what code and amendemnts that the local authority has adopted.Typically the NEC is adopted with only minor changes, but those changes are not always so minor and might be on point for this discussion.250.52"(7) Other Local Metal Underground Systems or Structures Other local metal
underground systems or structures such as piping systems, underground tanks, and
underground metal well casings that are not effectively bonded to a metal water pipe."While only 7 methods are listed #7 is fairly generic. And look at 90.4"90.4 EnforcementThis Code is intended to be suitable for mandatory application by governmental bodies
that exercise legal jurisdiction over electrical installations, including signaling and
communications systems, and for use by insurance inspectors. The authority having
jurisdiction for enforcement of the Code has the responsibility for making interpretations
of the rules, for deciding on the approval of equipment and materials, and for granting the
special permission contemplated in a number of the rules.By special permission, the authority having jurisdiction may waive specific requirements
in this Code or permit alternative methods where it is assured that equivalent objectives
can be achieved by establishing and maintaining effective safety.This Code may require new products, constructions, or materials that may not yet be
available at the time the Code is adopted. In such event, the authority having jurisdiction
may permit the use of the products, constructions, or materials that comply with the most
recent previous edition of this Code adopted by the jurisdiction."It looks like the AHJ has some leeway in acepting alternate methods."can't just dig another trench, the UFER has to be at the bottom of the foundation, as already pointed out after your post."The code says."(3) Concrete-Encased Electrode An electrode encased by at least 50 mm (2 in.) of
concrete, located within and near the bottom of a concrete foundation or footing that is in
direct contact with the earth, consisting of at least 6.0 m (20 ft) of one or more bare or
zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of
not less than 13 mm ( 1/ 2 in.) in diameter, or consisting of at least 6.0 m (20 ft) of bare
copper conductor not smaller than 4 AWG. Reinforcing bars shall be permitted to be
bonded together by the usual steel tie wires or other effective means."While the code clearly intends this to be for the footing/foundation for the building it does not say that. But as a funtional matter there is no operational difference if this concrete encased electrode is phyically on the bottom of a building. I don't see why an AHJ would not accept it at other places. The only arguement is that it might be distroyed by future construction.But a "foundation" for a driveway or a 4x5 storage shed might work."Clamps are not allowed as the conductor exits the concrete. Grounds have to be welded or crimped with an irreversible crimp if something happens to break continuity."That is not exactly what the code says."250.70 Methods of Grounding and Bonding Conductor Connection to Electrodes
The grounding or bonding conductor shall be connected to the grounding electrode by
exothermic welding, listed lugs, listed pressure connectors, listed clamps, or other listed
means. Connections depending on solder shall not be used. Ground clamps shall be listed
for the materials of the grounding electrode and the grounding electrode conductor and,
where used on pipe, rod, or other buried electrodes, shall also be listed for direct soil
burial or concrete encasement. Not more than one conductor shall be connected to the
grounding electrode by a single clamp or fitting unless the clamp or fitting is listed for
multiple conductors. One of the following methods shall be used:
(1) A pipe fitting, pipe plug, or other approved device screwed into a pipe or pipe
fitting
(2) A listed bolted clamp of cast bronze or brass, or plain or malleable iron
(3) For indoor telecommunications purposes only, a listed sheet metal strap-type
ground clamp having a rigid metal base that seats on the electrode and having a
strap of such material and dimensions that it is not likely to stretch during or after
installation
(4) An equally substantial approved means"Approved clamps can be used to connect ground electrode conductors to ground electrodes.The question is where does a the ground electrode end. Based on my reading of 250.52 (A)(3) rebar can be used for the electrode and I don't see anything that prevents it from exiting the top of the concrete.I don't know if there is an approved connector for copper to steel rebar that can be used when not encased in concrete..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
My home is built on rock. Rock out-croppings in the basement and garage, NO grounding rods here, I guess they figure the whole thing is grounded.
We just installed a ufer ground for a industrial building we just built. It was intentionally installed after the building was finished . The Electrical Engineer wanted it that way. We dug a 2' wide trench starting 6' from the building 20' long. We placed a #4 solid bare copper wire the length of the ditch and held it 2" off the bottom. We then poured a 8" thick piece of concrete. The EE said obviously the deeper the better but the only requirement was that the top of the concrete must be below the frost line. We then connected a piece of shielded wire that was run to the panel. The reason for the shielded wire was the EE said ware the copper wire comes out of the ground it will corrode if not shielded.
OK - great! - that gives me a 3rd alternative to pursue on Tuesday, although I'll have to call the electrical inspector to verify - especially the depth part.
In rocky soil, in fact in all soil I would just use an electric Kango or
T-83 or equivalent. I'm assuming you've tried that route. Can you use ground plates where you are? They are equivalent to two ground rods and can go in at 3ft or so. Otherwise, contact inspection. They can usually advise on alternatives.
>> In rocky soil, in fact in all soil I would just use an electric Kango or T-83 or equivalent <<
What's that? They used a medium sized demolition hammer (rotary hammer in hammer mode) with a special female ended bit on the first several tries. I personally have a medium small demo hammer but don't have the right bit. I looked around and couldn't find one although I didn't look very hard...
a T-83 is a grafics caculator...
maybe he was refering to a Hilti TE humongous....
but can't recall seeing an 83...
dunno the kangaroo....
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming<!----><!----><!---->
WOW!!! What a Ride!Forget the primal scream, just ROAR!!!
Sorry, that's a Hilti TE-83 which holds bits that are a little bigger in diameter than ground rods therefore ground rods just slip into the bit socket. But you've already gone that route. So I guess you are back to a ground plate, which is by far the easiest to install, if allowed or 20ft of #3AWG. bare copper(200A service) enclosed in concrete and set 2" from bottom (UFER). But before I went to that trouble, I'd contact inspection and see what they suggest.
Edited 6/3/2008 9:53 am ET by probey
Contact the inspection department in El Paso. This is not a unique situation and they will have the answer.