I have electric service installed on a pedestal next to my cabin. On this outside pedestal is the meter with a ground rod and and next to that an outside 200 amp breaker panel. The panel was installed to run tools while building and for power when camping. The panel has feed through lugs, meaning it has top lugs where the power comes in from the meter, then the main breaker, and at the bottom of the bus bar is a 2nd set of lugs. This is where I plan to hook up my lines running into the cabin. There will be 3, 4/0 aluminum wires plus a ground. 2 hot, 1 neutral and the ground. These will run underground in conduit and attach to my inside 200 amp panel. The ground bus and the neutral bus in the sub panel will not be connected and the neutral bus is insulated from the box.
I hope I have described this correctly and I think this plan is all up to code. My question is do I need to put in another ground rod at the cabin and connect it to the ground bus in the sub panel? The main panel and meter is about 30 feet from the cabin.
With a proper size ground wire between the main and the sub you don't need a separate ground rod at the cabin. But it is a good idea to have two ground rods at the main that are connected from one to the other at least 6 feet apart, but farther is better. 2X the length of the rods is considered better. The ground wire should be continuous from the panel through the first rod clamp and on to the second. There should be less than 25 ohms resistance; more than that makes the second rod mandatory under NEC. Wet ground is better than dry which is why we direct our gutter water to where the rods are. And if you only have one rod there is no effective way to check. Most contractors and inspectors do not test from what I am told.
I have your identical setup at the Cuyamaca Cottage. Don's right, the requirement was two 8' copper rods at least 6'apart. Two things you didn't mention, but I suspect you have done anyway since you're dead on with what you wrote--
1) The neutral and ground are bridged at the main panel
2) Your ground at the house is bonded to cold water line, gas pipe, and foundation
Oh---before you run your wires to the house, consider putting a power transfer switch just below the main. It's really hard to add later but easy to do now, then if you ever want to install a generator out at the pole it'll be easy. A 200 amp power transfer switch will cost about $324 new
This is what my power compant wante done I know your setup is a bit different but this explains the ground rod placement pretty good.http://dahlberglightandpower.com/wp-content/uploads/2013/06/Underground-to-Building.pdf (http://dahlberglightandpower.com/wp-content/uploads/2013/06/Underground-to-Building.pdf). And dont forget to wad the paste on those aluminum wires.
Ground rods can be angled if you can not run them straight down by the way. For example rocks and maybe that stupid piece of concrete no body know why it is there but it is. You can use a steel post driver - usually a heavy often weighted pipe about three foot long with handles on both sides. Like a small pile driver you can pound them in until you can get on them good with a double jack. (Long handled sledge hammer) ;) Because of rock we had to bed the ground rods for the service for the house and shop in the trenches. Grounded well because it was where we went through an intermittent creek and it was very wet down there. One ran toward the Idaho service drop and the other ran toward the shop both at angles. We got them in per code but every one I tried to drive went down about two feet and that was it so we angled them off into the conduit trenches.
Thanks for the responses, it sounds like I am on the right track.
flyingvan, I don't have any metal water lines or gas lines. Does that create a problem?
I have a cistern with a submersible pump and sched 80 pvc to the house. That is not plumbed yet and the plan is pex for in the cabin. There may be some points where copper will need to be used, not sure about that yet.
No problem at all----there's nothing for residents to ground themselves to.
The 4/0, 4/0, 4/0, 2/0 wire is called "mobile home feeder wire and is rated for direct burial but I would rather put it in conduit just for the extra insurance. Will this work in 2" pvc conduit or do I need larger?
Link http://www.menards.com/main/electrical/rough-electrical/electrical-wire/4-0-4-0-4-0-2-0-aluminum-mobile-home-feeder-per-foot/p-1469809.htm
I like your idea of conduit - we pulled similar but not direct burial. I think it was three inch we used
Re: Rick and Ellen's Homestead
« Reply #133 on: November 26, 2013, 04:43:01 PM »
There is a limit to how many wires of what size that can fit into any particular size of conduit. Set by NEC. This also varies with conduit type. It has to do with heat. There are temperature limits for the wires themselves. In conduit they run hotter.
I'm just finishing lunch and am in the middle of a project that keeps taking more time and can not find my bookmark, if I saved one. There is also an old topic here someplace on conduit and the number of wires that can be run. maybe try a search. There are links in it.
Myself I'd run the already approved for direct burial feeder wire in the ground. Buy a roll of "underground cable" marker tape. Partly fill the trench, lay the tape and finish burial.
If you do buy direct burial it is sort of redundant to buy conduit. But I like conduit for several reasons. With a good operator on a backhoe they can usually feel conduit if they are fishing..... Another reason I like conduit in my mind it will last longer. I have no bases for that opinion I suppose other than the old funeral thing of ash to ashes and dust to dust. And what ever you bury will some day return.
That said we have direct burial running all over here. Near each frost free I ran a direct burial 12 / 2 Romex. That has been so handy over the years..... Trench was open for the water pipes so we splurged and run the Romex..... ;)
My concern now is mostly the conduit size. The charts I have found say 4, 4/0 wires max out the 2 inch pvc but my fear is the mobile home feeder being direct burial has more insulation thus greater diameter.
I also had someone recommend another wire. It is a 4/0, 4/0, 2/0 and I guess I would have to get another strand of #4 copper or 2/0 aluminum for the ground. I thought I had read somewhere that in a sub panel the neutral needed to be the same size as the hots.
There is also another 4/0, 4/0, 4/0, 2/0 wire that has the 4 wires wrapped in a grey insulation but it is not rated for direct burial. Putting the direct burial cable in conduit seems like extra insurance against future problems.
I tend to be the same way, when I did my pool I put underground wire in the PVC piping just as an extra precaution. If you put a shovel into the ground you will have a hard time getting through the PVC, but the wire will immediately slice through... and then you are digging a new trench. Another possible positive, if the PVC is big enough, you could technically later run more wire without digging, just leave a string in there for "future use" and if one day you need a second line you do not have to dig, just pull and hope the line doesn't break. :)
How far are you looking at pulling your wire? It really does not sound all that far or ???
When we pulled ours with the larger conduit. It worked so easy. We used a lot of lube like a couple bottles -
Some say use dish soap or lard or my thinking why not use the real thing. Less chance of a reaction with the cable insulation..... In fact we shoved almost a third of it through before the guy on the excavator had to make his first pull.
Side note - my electrician - 'Electric Ray' an old guy but keeps on keeping on he does not like direct burial. But he is old school and kept telling me when we laid this all out out, "Now we can go direct burial but......" I never heard the reason after the but......
With conduit and that large wire you want the long arching sweeps not the shorter 90's.
I don't understand the ratinal behind putting DB wire inside conduit. If I wanted the insurance of using conduit (more resistant to a shovel poke than DB wire) then why not run THWN inside conduit? Which is what our 325 foot high voltage DC line at our cabin is.
Quote from: rick91351 on May 11, 2014, 01:25:39 AM
------snip----------
That said we have direct burial running all over here. Near each frost free I ran a direct burial 12 / 2 Romex. That has been so handy over the years..... Trench was open for the water pipes so we splurged and run the Romex..... ;)
The direct burial 12 /2 was buried like 4 feet so I am not going to stumble on it..... We were using the big excavator of my logging road making neighbor - my ol' buddy - ol' pal.......
Quote from: MountainDon on May 11, 2014, 09:32:03 AM
I don't understand the ratinal behind putting DB wire inside conduit. If I wanted the insurance of using conduit (more resistant to a shovel poke than DB wire) then why not run THWN inside conduit? Which is what our 325 foot high voltage DC line at our cabin is.
I see MD's point here and sort of my own as well ties in. If you are using conduit why use direct burial unless you can get a heck of a deal on it. With our distance necessitated larger wire. I had bought the conduit we used several years ago knowing what we were going to have to do. It sat stock piled here. But then as I say Electric Ray he does not like direct burial and he liked my pile of conduit - ;)
As far as the fear of a shovel into DB I really don't think that is going to happen. A non informed backhoe operator will pull everything loose as will track hoes and excavators. However a good operator on a backhoe that he knows and uses many times can fish and find without to much damage. :D One of the guys the works for our telephone company up here is a master of it. I am first to admit I am not one of those. ;)
The question is, is it legal to pass normal wire in PVC, or does code require it to still be underground rated if buried? If you are running any amount of length, then the cost factor is major. In my pool case it was only 50 feet. The PVC was to prevent a shovel accident, but the underground wire was to protect from water. Regular wire is not rated for water contact, and who knows how water tight my connections would be with the PVC, especially with frost heave, so why take the chance. That was my take anyways, kind of a double protection, especially that it was for a pool. I would not hesitate to do the same for my generator connections... just extra protection.
What is normal wire? Romex? That can not go in a conduit, underground mainly because conduit is considered to be a wet location and ordinary Romex is only for dry indoor areas. It's the insulation that needs the wet rating. You can run UF type in conduit underground.
Most THHN sold today is also THWN, where W = wet. Many places don't list the THWN on the tags on the sales shelves. Look at the wire and see if it imprinted THHN/THWN; then it can be placed in conduit. When I bought wire for the cabin PV to CC lines THHN/THWN was cheaper than any direct burial types even including the conduit. I have not looked recently.
An advantage of conduit over direct burial is depth of trench needed. Most places let conduit be shallower; at least here does. Individual single conductor wires are also going to be easier to pull, IMO.
I'm going to check with some of the electrical supply places today. The big box stores are limited as to what kind of wire they stock. The only large service entry wire that HD stocks is 3/0 copper. That's almost $3 per foot X 3 plus a ground. That gets expensive fast.
Quote from: grover on May 12, 2014, 06:50:07 AM
I'm going to check with some of the electrical supply places today. The big box stores are limited as to what kind of wire they stock. The only large service entry wire that HD stocks is 3/0 copper. That's almost $3 per foot X 3 plus a ground. That gets expensive fast.
That is why we went with the aluminum. I never have use it before but it was a lot less.
Electrical supply house recommended 4/0 4/0 2/0 alum and add a #4 or #6 copper for the ground. Is it ok to downsize the neutral to 2/0? I'm running this about 70 ft.
Around here HD sells 4/0 4/0 2/0 4 USE cable for mobile homes. It is on the website
Putting the underground wire in conduit will keep it from getting destroyed by rocks as the soil settles
Quote from: grover on May 12, 2014, 05:37:39 PM
Electrical supply house recommended 4/0 4/0 2/0 alum and add a #4 or #6 copper for the ground. Is it ok to downsize the neutral to 2/0? I'm running this about 70 ft.
I asked my master electrician friend about that when I was doing mine and I believe he called it an unbalanced neutral and that I would have to check with the locals if they approved it he said some do and some dont . I ended up using individual strands of 2/0 copper for all conductors and #4 copper for the ground as per his recommendation.
I've decided to go with the 4/0 4/0 4/0 2/0 mobile home feeder wire and put it in conduit at least 18 inches below grade. I have not decided yet whether to go with 2 1/2 or 3 inch conduit.
This is my question now...I am thinking about going through the concrete block down below grade and come into my crawl space into an LB then go up and along the bottom of my floor joists and up into my panel. The reason for this is for the future possibility of putting a deck on that portion of the cabin and an LB on the outside would be in the way. I haven't found anything that says I cannot do that. The only thing I have seen is I need to put the conduit inside another piece of conduit where it goes through the block.
Any problems with this?
Thats similar to how i powered my shop ran the conduit up from the house panel through 15' of floor joists outside and buried then back up and in to the shop inspectors seemed mostly concerned how deep the pipe was in the ground. it is common to uses pipe within pipe going through masonry.Use lots of that electrical lube when your pullin the wire helps alot best to use 2 or 3 people 1 to pull 1 to push and 1 to lube the wire Ive seen people pull it through using a pick up truck also.
Quote from: grover on May 06, 2014, 08:55:09 PM
My question is do I need to put in another ground rod at the cabin and connect it to the ground bus in the sub panel? The main panel and meter is about 30 feet from the cabin.
As has been said, the answer here is no, you don't need to. More importantly (the reason why I'm posting), doing so would be not only a code violation but potentially a major safety hazard. You want one AND ONLY one ground connection on each power system. If you drive a separate ground rod at a sub panel, you've created parallel ground paths, meaning it's possible for current to use the ground as a return, meaning anything grounded could become a current-carrying conductor (such as grounded metal equipment housings, like your microwave, toaster, washer, etc). Bad news!
Code specifies (in a residential application) one neutral to ground connection: at the main service entrance (which you have). Do not make a second one anywhere on the same system.
Quote from: _JT on May 25, 2014, 07:57:54 AM
As has been said, the answer here is no, you don't need to. More importantly (the reason why I'm posting), doing so would be not only a code violation but potentially a major safety hazard. You want one AND ONLY one ground connection on each power system. If you drive a separate ground rod at a sub panel, you've created parallel ground paths, meaning it's possible for current to use the ground as a return, meaning anything grounded could become a current-carrying conductor (such as grounded metal equipment housings, like your microwave, toaster, washer, etc). Bad news!
Code specifies (in a residential application) one neutral to ground connection: at the main service entrance (which you have). Do not make a second one anywhere on the same system.
w* Thanks well explained..........
Quote from: _JT on May 25, 2014, 07:57:54 AM
As has been said, the answer here is no, you don't need to. ....................
................Code specifies (in a residential application) one neutral to ground connection: at the main service entrance (which you have). Do not make a second one anywhere on the same system.
Just to be clear on this...... The presence of a ground rod does not necessarily mean there is also a bond between the neutral and the ground. It is absolutely true true that there should only be ONE BOND in a system, but I'm not certain if the presence of a ground rod (W/O a Bond connection). ??? If the subpanel is detached from the main panel is it not OK to ground the sub panel to Earth as long as there is No Bond at the subpanel?
I'm asking because the OP was questioning the sub ground rod and Did state that the sub panel would Not have any Bonding.
MD I did not catch that about the non bonding issue..... ??? Not following you on this one......
Keeping up with current events---
I was required to bond my subpanel at the house to the foundation, gas piping (which is buried in the yard) and cold water lines, so I suppose grounding each panel is a good thing. I'll echo what was said, too---the ground and neutral are only bonded at the main panel, nowhere else.
Objectionable Current--
http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/ObjectionableCurrent~20020610.htm
If I understand Grover's situation there is a pole with meter and a main panel in the ground outside. This was the construction meter/panel system. Now the cabin is built and the cabin will have a panel inside, connected to the outside panel. Outside = Main; inside = sub panel. Or am I misinterpreting something?
The Bond is the connection between the neutral bus in the main panel and the ground bus in the same main panel. There must be only one Bond in a system. That should be at the main. If the main was removed and there was only a panel inside then the Bond would be there. Anybody with information that indicates that is wrong can, should, please point out the error in my thinking so I can correct myself, my info. Thanks. References or explanation of where to look would be appreciated.
Quote from: MountainDon on May 25, 2014, 09:32:12 AM
Just to be clear on this...... The presence of a ground rod does not necessarily mean there is also a bond between the neutral and the ground. It is absolutely true true that there should only be ONE BOND in a system, but I'm not certain if the presence of a ground rod (W/O a Bond connection). ??? If the subpanel is detached from the main panel is it not OK to ground the sub panel to Earth as long as there is No Bond at the subpanel?
I'm asking because the OP was questioning the sub ground rod and Did state that the sub panel would Not have any Bonding.
Excellent question, Don. I wasn't addressing the OP because I wanted to interject and emphasize the neutral/ground bonds. The answer to your (and his) question is yes, it's fine to install a ground rod at a subpanel so long as you
make sure you remove the bonding strap between neutral and ground bus. In fact, in some localities I believe the ground rod is required (for a subpanel in a detached structure).
ETA:
250.32 Buildings or Structures Supplied by a Feeder(s)
or Branch Circuit(s).
(A) Grounding Electrode. Building(s) or structure(s) supplied
by feeder(s) or branch circuit(s) shall have a grounding
electrode or grounding electrode system installed in
accordance with Part III of Article 250. The grounding
electrode conductor(s) shall be connected in accordance
with 250.32(B) or (C). Where there is no existing grounding
electrode, the grounding electrode(s) required in 250.50
shall be installed.ETA2: Apparently, it gets even more interesting than I'd previously thought. In some cases (depending on what version of the code you go by and how old your structure is) it's ok to bond neutral and ground again in a subpanel for a detached structure, provided it's a 3 wire feeder (that is, 2 hots and a neutral; no ground connection to the main panel). I was not aware of this wrinkle, although I maintain that best practice is to isolate ground and neutral at the subpanel and drive a new ground rod (possibly 2), connected to the ground bus of your panel.
Quote from: MountainDon on May 25, 2014, 11:12:02 AM
The Bond is the connection between the neutral bus in the main panel and the ground bus in the same main panel. There must be only one Bond in a system. That should be at the main. If the main was removed and there was only a panel inside then the Bond would be there. Anybody with information that indicates that is wrong can, should, please point out the error in my thinking so I can correct myself, my info. Thanks. References or explanation of where to look would be appreciated.
Correct. With a caveat. The 'main panel' is the panel that has your main breaker for your entire supply (commonly 200A 2P for residential supplies). Whether that panel is located inside the house or outside the house doesn't change that, and you'll only have one main breaker, regardless of how many subpanels there are or where they're located.
Section 250 of the NEC has all the info you could ever want on grounding, although you must supply your own headache medicine. :)
I'm OK [cool] [cool] I remember my buddy the electrician - (now owns a coffee shop and no electrical licence.) (( Says less headaches and more $$)) When I ran my sub panel to the RV pads he had me do exactly what you posted. I removed the bonding strap and drove in a ground rod. At that time I think you could get by with just the one.
Thanks for the clarifications _JT. Much appreciated. Electrical can be confusing.
Indeed! I do it for a living and still get twisted up around the code requirements fairly regularly.
A marginally related question I've had (since Rob_O brought it up in the portable generator thread)--- My backup generator is isolated by a power transfer switch, but only the hots---not the neutral. I took a close look at the wiring schematic for the generator and I don't see anywhere where the neutral and ground are bonded, so it's still only at the main panel.
Without the neutral being switched, is there any situation where I'd be energizing the neutral beyond the cottage? It doesn't seem like it---I'd think the sum of the two legs would always equal the neutral at the generator, and NEC doesn't require the neutral to be isolated, but I want to be sure---don't want to harm any repairmen, and our power gets knocked out often
Just so I'm clear, the question is: is it possible for your generator, while running, to energize the neutral at your house, possibly backfeeding back through your transformer and energizing the overhead powerlines?
If your neutral and ground are properly bonded at the main service entrance as required by code, the answer under all circumstances I can think of is no. The reason that ground connection is required in residential applications is so that, if there is a ground fault (hot wire shorts directly to ground), the fault current is high enough (because the impedance between neutral and ground is very low [direct bond]) that a circuit breaker trips. The breaker protecting whichever hot contacted ground. So energized neutrals are not something we should ever see on a properly connected residential system.
If things have gotten horribly miswired, I suppose it would have to consider that a possibility. Though still an unlikely one.
Yes, you answered my question, thanks!
I'll throw myself under the bus here with the only wiring mistake I made (that I'm aware of----it's been completed for well over a year and all is well so far) and I corrected it before I actually ran the generator----
(http://4.bp.blogspot.com/-mCDzplwTDKE/Ujtfr6VZebI/AAAAAAAACAs/5gYlWU_ljIs/s400/sept+switch.JPG)
A panel in a detached structure is required to have a made electrode (rod, pipe, plate ufer etc) NEC 250.52. If the ground is not brought over do not separate the ground and neutral from each other since you are not allowed to use the earth as a ground conductor since it will not reliably trip a circuit breaker. If the ground is brought over use a separate ground bar for the ground and isolate the neutral.
NEC 250.52 requires another made electrode at the separate building. a ufer is the preferred method.
ground rods are not to be driven at an angle to exceed 45 degrees. If a rock bottom is encountered they can be laid in a trench at least 30 inches deep.
The downsized neutrals are permissible if the load on the neutral does not exceed the capacity of the wire, do a load calculation to determine the loads on the various conductors. typically a few of the loads will be fairly large 220v loads that do not use the neutral, also the neutral only carries the unbalanced load of the other two conductors. harmonic loads such as computers and fluorescent lighting can cause a large neutral load but these are generally only seen in commercial installations some can require oversize neutrals.
On the question of how many ground rods are required, the NEC requires a ground of 25 ohms or less, that could be one electrode. How ever The IRC may require two, this is a requirement put there in order to be different than the NEC it protects them from copy right infringement. IRC requirements will be more stringent than NEC or uniform building codes because they have to make changes to protect themselves from copying the other published codes. Writing code books is a multibillion dollar industry. hundreds of thousands of jurisdictions buying books at more than 100.00 each and thousands of contractors buying them as well. If you use the IRC your structure will cost thousands more than if you follow the NEC and the rest of the uniform building codes. the authority having jurisdiction chooses what codes to use it's usually a Hodge podge of codes based on the preferences of the head inspector.
Thanks for resurrecting this, my barn is wrong d*
I ran 4 wires; 2 hots, a neutral, and a ground from a breaker in the main panel. There is a bonding jumper in the panel in the barn from neutral to ground. So as I'm understanding this, the current would be just as happy to take either path back to the main panel. Or, if I grab Dad's old metal bodied non double insulated saw and walk outside barefoot, the return path is just as happy through me. I'm understanding that I need to disconnect the bond and isolate the neutral from the ground. Then, it is a good idea to drive another ground rod at the barn hooked only to the ground.
At last check I think 48 states were under the IRC, code adoption is at the state level rather than the jurisdiction level. An AHJ can try anything, you have to know when he is piling it on and call it sometimes. I can't speak to the NEC but I'll bet it is incorporated into code by direct reference as are other documents like the NDS, copyright isn't an issue... Somewhere in the depths of one of the later chapters of the IRC. But no doubt about it, the ICC is the international cash cow. Although, I haven't had to buy a codebook in well over a decade, it has been freely available online. IMO all laws should be chiseled in a stone set in the village square for all to see.