# Wiring new shed, ground rod?



## thinkxingu (Apr 5, 2010)

Hi All,
     Next Saturday, I'll be wiring up my new shed (built August of last year) and there are two electricians involved: a good friend and my brother-in-law!  One says I should use a ground rod out in the shed, the other says I shouldn't.

I'll be running 8AWG wire to a 6-breaker panel (100' run) just in case I want to ever add 220 out there.

What do you think?!

S


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## seige101 (Apr 6, 2010)

Yes, since it will be considered an outbuilding with a seperately derived system. (at least i think thats what i wanna call it, no coffee yet though) You will need to run 4 wires to the subpanel, 2 hots a neutral and a ground. What size 220 loads would you ever be using out there? I would upsize the wire to #6 to reduce any voltage drop.


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## PapaDave (Apr 6, 2010)

Might have been overkill, but I ran #2 out to my pole barn about a 70' run.
Oh, and a sparky my brother knows said to use 2 rods at least 6' apart, 8 ' deep. Did that too.


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## woodsmaster (Apr 6, 2010)

I'm not an electrician but I was told (not by an electrician) that if your running a wire with a ground  from a panel box it will be grounded at the panel box. If the wire you run don't have a ground you obviously have to use a 
seperate ground rod at the building.


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## vvvv (Apr 6, 2010)

Cant have enough grounds! The more the better.


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## oldspark (Apr 6, 2010)

Why would you not ground it, all saftey codes call for grounding and been this way a long time.


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## woodsmaster (Apr 6, 2010)

oldspark said:
			
		

> Why would you not ground it, all saftey codes call for grounding and been this way a long time.



Wouldn't it be grounded threw the ground wire that runs to the panelbox in the house and altimitly the house ground rod ? Don't know the codes not an electrician but my shed has elec. with no ground rod. Should it be changed.


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## lobsta1 (Apr 6, 2010)

> Oh, and a sparky my brother knows said to use 2 rods at least 6’ apart, 8 ’ deep.





> Yes, since it will be considered an outbuilding with a seperately derived system. (at least i think thats what i wanna call it, no coffee yet though) You will need to run 4 wires to the subpanel, 2 hots a neutral and a ground. What size 220 loads would you ever be using out there? I would upsize the wire to #6 to reduce any voltage drop.



I believe this is correct. Also, I believe that you have to remove the jumper strap in the subpanel that is between the grd bus & the neutral bus.
Al


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## billb3 (Apr 6, 2010)

You're gonna need a ground rod for the TV antenna anyway.


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## fbelec (Apr 6, 2010)

billb3 said:
			
		

> You're gonna need a ground rod for the TV antenna anyway.



LOL   got that right


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## fbelec (Apr 6, 2010)

here in mass ( might be a national code) since it is a separate building you need a ground rod 8 feet long. only one. and the wire you run from your house panel needs to be 2 hots a neutral and a ground and then at the sub panel in the shed separate the ground bar from the neutral bar via the ground strap or the green screw on the neutral bar that goes thru the neutral bar and is screwed into the back of the panel. (depends on the brand panel you have) if you are using a #8 copper you can only use a 50 amp breaker or aluminum use a 40 amp breaker. i just did a sub panel in a garage i used # 4 aluminum and a 60 amp breaker for a 110 foot run inside 1 inch pvc pipe. don't forget to install expansion fittings on the pipe above the ground. one ground rod. the inspector said it was a nice job.


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## benjamin (Apr 6, 2010)

Two schools of thought here, 

1.  the more ground rods the better

2.  the shed is a subpanel off of the house service, the house service has the neutral bonded to the ground, but any subpanel has to have the neutral isolated from the ground. One ground bar that is bonded to the box and one neutral bar that is insulated from the grounded box.

I think there are instances where it's not desireable to have multiple paths.  I don't recomend this, just trying to explain the logic.

Obviously if you're running three wires, two hot and one neutral, you ground your neutral.  If you run a seperate ground and neutral, I'd still add one or two ground rods, but keep the neutral ungrounded.  

Not an electrician, but my work has always passed.  I try to avoid quoting the code since the time I tried to explain something electrical to an uncle whose wiring I had just fixed and he pulled out his copy of the code (hard cover full edition) and showed me his name on the list of authors.


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## dancarbo (Apr 6, 2010)

The National Electrical Code Section 250-32 (B) Exception: permits the supply to an existing (not new) second building to consist of two ungrounded hot wires and one grounded neutral conductor, with the neutral conductor grounded and bonded to the service enclosure at the second building and tied to a grounding electrode. This does not apply if there is any other metal connection between the two buildings. (example; metal water pipe) 

Any other situation that does not fit the exception would require a forth grounding wire from building to building bonded to both service boxes.

Since your building existed prior to the wiring I feel that you should come under the exception. But if you have to have it inspected, You should run this past the inspector.

Hope this will help.

Dan


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## hkillam (Apr 6, 2010)

I agree with "permits the supply to an existing (not new) second building to consist of two ungrounded hot wires and one grounded neutral" and believe this is the proper and current NEC method. As for grounding rods, don't stop at the minimum requirement; drive at least two rods, and consider their location. Moist soil (under a downspout, or at low ground where water will puddle during hard rain) is best, gravel or other agregate is bad. Cant tell you how many houses I've seen with a single rod, driven in the most convenient place by the rushed electrician, that were in mostly backfill of gravel, right next to the foundation. And passed inspection. You only have to put in a grounding system once if you do it right.

I think that the best source of understandable material on this subject (and I've read many) is "Wiring a House (Best of Fine Homebuilding)" by Rex Caldwell. Very good information, understandable, and goes into detail about where "Code Minimum" isn't enough.


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## dancarbo (Apr 6, 2010)

I agree with Hugh K. that one grounding rod may not be enough as the NEC is a minimum standard. The NEC says that if the ground rod does not have a resistance of 25 ohms or less to earth then a second ground rod is required. The second rod should be driven a minimum of six feet away. Since we have no practical method of measuring the resistance to ground (an ohmmeter will not work) additional ground rod or rods would be a good practice.

Dan


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## oldspark (Apr 6, 2010)

If done correctly there is no reason in the world to have two ground rods on one building that I can think of.


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## oldspark (Apr 6, 2010)

The reason for the ground rod at the building is if there is a short to ground you do not tear up any more wire and equipment than necessary so each building shoud have it's own ground.


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## Deere10 (Apr 6, 2010)

GROUND it    Well worth the effort.  I put up a shed last year and only have a couple circuits in it but still drove the 8ft grd rod in.Especially if lookin at 220 in the future. Do it now and do it right..


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## Later (Apr 6, 2010)

We lost the neutral on our underground service a couple of years ago. The electrician who traced the break and repaired it also put in a "ground plane" consisting of multiple rods a spaced a couple of feet apart. He had said at the time that if we had the ground plane  when the neutral broke, our equipment damage would have been quite a bit less, as a matter of fact we might not have noticed the problem right away. Don't think that he was blowing smoke, he only charged $50.00 for the rods, wire, and installation.


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## oldspark (Apr 6, 2010)

Retired Guy said:
			
		

> We lost the neutral on our underground service a couple of years ago. The electrician who traced the break and repaired it also put in a "ground plane" consisting of multiple rods a spaced a couple of feet apart. He had said at the time that if we had the ground plane  when the neutral broke, our equipment damage would have been quite a bit less, as a matter of fact we might not have noticed the problem right away. Don't think that he was blowing smoke, he only charged $50.00 for the rods, wire, and installation.


 Why would losing a neutral cause damage to equipment, not sure I understand that.


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## Later (Apr 6, 2010)

The way that it was explained to me is that the lost neutral caused the ground to float. The symptoms that we experienced were that the 240V service wasn't split evenly into two 120V legs, but some circuits saw 180V when others were at  60 volts, even this wasn't constant just varied all over the place until I opened the main breaker.


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## oldspark (Apr 6, 2010)

Retired Guy said:
			
		

> The way that it was explained to me is that the lost neutral caused the ground to float. The symptoms that we experienced were that the 240V service wasn't split evenly into two 120V legs, but some circuits saw 180V when others were at  60 volts, even this wasn't constant just varied all over the place until I opened the main breaker.


 Interesting, not sure why a lost neutral would cause the ground to "float" as it still should have been connected and functioning. How much stuff did it ruin?


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## Later (Apr 6, 2010)

Microwave, small cheap TV, light bulbs and I think it shortened the life of the refrigerator - died a few months later. With our sandy soil the single rod that we has may not have worked well as a ground.


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## Highbeam (Apr 6, 2010)

Those are all 110 loads so what happened is that your AC circuit was broken intermittently since it had a good hot wire. The push pull of AC wasn't able to push and pull too well so the voltage potential varied up to 110. Shouldn't have seen any higher voltage than 110 on those circtuits. Now your 220 circuits don't even use the neutral so they should have been fine.

I have always been told that a subpanel at an outbuilding gets its own grounding system including ground rods. It will look just like a service entrance from the street where you only need three wires from the house. Hot, hot, and neutral. The ground will go to the rods.


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## fbelec (Apr 7, 2010)

if you lose your neutral your ground better be good, or you'll lose anything that is not 240 volt. i had a case in my town here last year. the guy lost his ground and his neutral he lost 3 tv's, 3 cable boxes, his computer in his furnace, multiple light bulbs, 2 fluorescent ballasts, a computer, and a freezer. you got to see a 2 bulb fluorescent 4 foot fixture with 185 volts going to it. as bright as a 8 bulb fixture. back to grounding. check with the inspector of your town. we got a guy up here that doesn't care if you have a water pipe ground, if you do a panel change or service change he wants to see two ground rods hooked up. even tho codes say when you have a water pipe ground the addition of a supplemental ground rod has to be installed (that's one. he wants two.) if you question him on the code he asks for a ohm reading on that one rod, knowing that the only meter that can test that is what we call in the trade as a mega meter. they cost at minimum $1000.00 i don't know anyone around here that has one. in my opinion put one in, the rod costs $15.00 and some #6 copper wire. most guys will want to see a rod because if your running all aluminum conductors because copper is ridiculous as far as price goes, they want a good path to ground, the aluminum will blow apart quickly, the copper won't. there have been times when a out building has a bad ground or no ground and starts getting fault currents that would normally blow the breaker but didn't and were felt a mile away at some other barn where the cows stopped making milk and refusing to either go inside or outside. i have a electrician friend that was doing a panel change and got wacked off the neutral when installing it into the grounded panel. he got hit off the utility neutral because his was the only good ground on the street. long short, install a ground rod.


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## fbelec (Apr 7, 2010)

Highbeam said:
			
		

> Those are all 110 loads so what happened is that your AC circuit was broken intermittently since it had a good hot wire. The push pull of AC wasn't able to push and pull too well so the voltage potential varied up to 110. Shouldn't have seen any higher voltage than 110 on those circtuits. Now your 220 circuits don't even use the neutral so they should have been fine.
> 
> I have always been told that a subpanel at an outbuilding gets its own grounding system including ground rods. It will look just like a service entrance from the street where you only need three wires from the house. Hot, hot, and neutral. The ground will go to the rods.



it will see higher and lower voltages. got to see it first hand. when i got to this guys house he had 60 volts on one phase and 180 on the other. it would change with the different loads put on each phase. when i shut off his main everything was normal as far as measuring the voltage from phase to phase and from phase to ground. turn on his breaker and the voltage varied. thought it was a bad main breaker so i changed it. still the same. power company came and fixed the center tap on their wire at the pole and everything was normal. he still needs a new ground but won't here of it. so we wait for the next time it happens to him so that he can buy all new electronic.


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## oldspark (Apr 7, 2010)

He needs the ground and I understand why he asked the question now, but getting off track I do not know why you need a megger for the ground rod reading, and they do not cost a 1,000, I have an old one but if I was to check the ohms on a ground rod I would just use my meter, the megger is a better tool for some things but not sure why you would use it in this case.


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## oldspark (Apr 7, 2010)

Actually I looked it up and you do not use a meter or a megger, they make a special tool for checking the ground rod, the code person should be the one checking it not you, I would call him out on that.


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## fbelec (Apr 7, 2010)

oldspark said:
			
		

> Actually I looked it up and you do not use a meter or a megger, they make a special tool for checking the ground rod, the code person should be the one checking it not you, I would call him out on that.



hi oldspark

can you point me in the direction of this ground rod checker. the inspectors around here want it done with a megger. i don't know why, but thats what they want. and if the fix to getting my job to pass inspection is cheap like a extra ground rod thats what i do. but now if there is ground rod checker i need to know for less work.

frank


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## oldspark (Apr 7, 2010)

fbelec said:
			
		

> oldspark said:
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 Oh boy, can of worms, the testers are pricey and I guess there is a way to do it with a megger, (3 point test) and the second ground rod is what some people recomend, just do a google search and the can of worms tips over. My thought was if the soil is not that good why would 2 be better than one. This subject is worse than some of those related to wood burning here on hearth.con! :lol:


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## fbelec (Apr 7, 2010)

oldspark said:
			
		

> fbelec said:
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nah. dealing with the inspectors that interpret the code wrong or different, or just want to have a big head. thats tuff.


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## Tony H (Apr 7, 2010)

Ground rod Yes YOU WANT ONE  when it's needed you want the shortest straightest path to ground to minimize damage to life and property. 
You will only need a single ground rod for a shed and most buildings . We would only install ground plains when the ground was poor and we has lots of telephone and data equipment to protect.


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## fbelec (Apr 7, 2010)

Tony H said:
			
		

> Ground rod Yes YOU WANT ONE  when it's needed you want the shortest straightest path to ground to minimize damage to life and property.
> You will only need a single ground rod for a shed and most buildings . We would only install ground plains when the ground was poor and we has lots of telephone and data equipment to protect.



hi tony 
i've never done a ground plane. what's involved with doing it?


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## feelingasi (Apr 7, 2010)

the best way to do this is to go buy some direct bury mobile home wire 2-2-2-4al, its about 1.80 a foot. put it in pipe. 1 1/4 is possible but 2" would be better.no more than 360 deg of bend in the pipe. bury a couple spare 3/4 for future. you may want to add a light that you can controll from the house,cable,internet, etc???. with the 4 wire system you should not install a ground rod. by doing so you establish a parallel path for fault current to travel in. this is an unlikely occurance but it can happen. at any one property, consisting of one service, the main panel should be the only point in the electrical that is bonded if you want to add a ground rod there go ahead. the #4 should be hooked to an auxillary ground bar inside your subpanel(you will have to purchase this separate), and do not bond the nuetral. all nuetrals from branch ckts go to nuetral bar, all bares or greens go to aux grnd bar. being in your shed does not make it any different that being a sub panel anywhere else in your home. it is not a separately derived system as it is not a standalone service nor is it derived from a XFMR. If you need code sections i will be more than happy to look them up. I'm just being lazy right now. 15 yr IBEW inside wireman.


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## Tony H (Apr 8, 2010)

fbelec said:
			
		

> Tony H said:
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The terminology may not be correct but what we called a ground plane was not the typical RF antenna version but simply a series of ground rods tied together to provide a better ground and larger capacity from the building / equipment to ground.
What we did was put in five ground rods laid out in a grid with one central rod and the four other laid out in a somewhat box shape 6' to 10' apart and tie them all together and back to a ground bar and then a couple of grd wires back to the building. 
There was a formula we used for sizing the wires.


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## fbelec (Apr 8, 2010)

ya i know what you mean. i can't remember the name either. we do a ground like that on inground pools.


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