# Ground rod or not?



## jimmy21 (Jul 2, 2008)

install ground rods and keep the nuetral and ground bonded together other on the subpanel




.......corrected


----------



## brotherman (Jul 8, 2008)

seperate neutral and ground from one another? Neutral wire to neutral bar, and ground wire coming from ground rod to equipment ground in subpanel?

talking about electrical work, I probably sound ignorant, so please excuse

Thanks,
chad


----------



## jimmy21 (Jul 2, 2008)

err wait, i screwed up on that, i was typing without even thinking. You want them together. There will be two seperate bars, and on the subpanel you buy there will probably be a green screw that you will need to screw in through the nuetral bar tying it to the panel can. Or sometimes there is a bar that you tie the two together. Either way, you need to make sure there is conductivity between the two


----------



## Pudge565 (Jan 27, 2008)

I thought that you do want them isolated in a sub panel? I may be wrong since it is a detached building but I don't know


----------



## BigJimmy (Jun 30, 2006)

Doesn't matter if it's 15ft or 115ft. Separate the ground and neutral busses in the detached power panel, drive a rod and bond to the ground bus, and run a ground wire to the source panel. The important thing here is that, unlike your service panel, the ground and neutral busses must be separated electrically.


----------



## jimmy21 (Jul 2, 2008)

Pudge565 said:


> I thought that you do want them isolated in a sub panel? I may be wrong since it is a detached building but I don't know


if its in the same building you would. in a separate building you want to drive ground rods and separate the ground and neutral


----------



## Pudge565 (Jan 27, 2008)

jimmy21 said:


> err wait, i screwed up on that, i was typing without even thinking. You want them together. There will be two seperate bars, and on the subpanel you buy there will probably be a green screw that you will need to screw in through the nuetral bar tying it to the panel can. Or sometimes there is a bar that you tie the two together. Either way, you need to make sure there is conductivity between the two


Ok this is why I asked cuz in this post your telling them to keep them bonded.


----------



## Stubbie (Jan 7, 2007)

Depends on what code cycle your inspector is using. Prior to the 2008... 120/240 volt feeders to *detached* buildings could be 3 wire H-H-N.....unless another metallic or conductive path existed (metal water pipe, data com cables etc..) then you are required to run a 4 wire feeder H-H-N-Grd. If your inspector is using 2008 then 4 wires are required as the 3 wire feeder is no longer allowed.

Prior to 2008 NEC Cycle (no metallic path other than feeder) 1st image....2nd image is 2008 ( I made the drawing in 2004 as a 4 wire feeder BUT is now required in 2008)


----------



## BillyD (Mar 15, 2008)

In your 3 wire feeder you show the Neutral and ground bonded. Everything we read says the neutral has to be isolated in a sub panel.


----------



## HouseHelper (Mar 20, 2007)

BillyD said:


> In your 3 wire feeder you show the Neutral and ground bonded. Everything we read says the neutral has to be isolated in a sub panel.


The three wire feeder functions just like the three wire feeder to your main service. The neutral and ground are bonded, to each other and the enclosure. You need ground rods whether you use three or four wire feeders. As Stubbie pointed out, if 2008 codes are in effect in your area, only four wire feeders are now allowed to detached buildings, with neutral and ground separated.


----------



## Pudge565 (Jan 27, 2008)

Ok thank you to all of those especially stubbie who clarified this subject for those of us that were a little confused.


----------



## BillyD (Mar 15, 2008)

Here is what was posted by the "kctermite" a couple of months back.


thekctermite said:


> A sub panel is fed off of the main panel using a double breaker that catches both the A and B phases. The feeder wires are sized based on the size of the breaker in the main panel that serves the sub panel.
> 
> In a sub panel, the circuits' neutrals must float...Or be isolated from the grounds. The neutral bar must not be bonded to the panel jacket. This is incredibly important.


----------



## J. V. (Jun 1, 2007)

BigJimmy said:


> Doesn't matter if it's 15ft or 115ft. Separate the ground and neutral busses in the detached power panel, drive a rod and bond to the ground bus, and run a ground wire to the source panel. The important thing here is that, unlike your service panel, the ground and neutral busses must be separated electrically.


This is absolutely correct. 
And you must not use the neutral bonding screw either. If it is installed you must remove it. 
Neutrals and grounds need to be seperated as BigJimmy said.
Since you are installing this new and have not pulled any conductors, just go with the four wire system. Your local jurisdiction may require this anyway depending on the code cycle they are following. Re: Stubbie.
You also will need a main breaker for the 100 amp sub panel. You need # 3 conductors (3) and a # 8 (1) ground. PVC conduit would be my choice on this project. You have to dig a trench anyway.
You may also be required to drive 2 ground rods. 
Finally, are you getting a permit for this installation? If not, you are making a huge mistake. While permits add to the job cost and inspectors can be *******s, at least you will know that you have a compliant and safe installation.


----------



## HouseHelper (Mar 20, 2007)

A true statement by the distinguished mr kctermite. For a subpanel in the same structure as the main panel, it is a requirement that the panel be fed with four wires and that the neutral and ground be isolated. No exceptions.

The difference is for a *detached structure.* Prior to the 2008 code cycle, you could feed a detached structure with three wires and bond the neutral and ground, *as long as* there were no other metallic paths between the buildings. That option has now gone away, and not soon enough in my opinion.


----------



## jimmy21 (Jul 2, 2008)

yes, i stand corrected. i wasn't aware it had changed. but it is true. Now you must take a ground and nuetral, seperate them, and still drive ground rods if its detatched


----------



## Stubbie (Jan 7, 2007)

Hello Billy

If you are still confused as to *why* we bond 3 wire neutral and ground and we don't bond neutral and ground on 4 wire feeders let us know and we will explain.


----------



## BillyD (Mar 15, 2008)

It is still very confusing because we read so many different interpretations of how to do sub panels. You posted the following on 5/8/08 and it does not mention 3 or 4 wire feeds or detached building. so it is confusing. If a 3 wire needs to be bonded and 4 wire isolated I get it. If not I am still lost. 
_*As previously mentioned the neutral and ground are bonded at the main panel only. You seem to not quite understand why this is required and it is probably because you are confused between ground and neutral. the white taped neutral in your panel is the service neutral or commonly called the service grounded conductor. Grounded means intentionally connected to earth which is given a Zero (potential). So any voltage measurements from an ungrounded (hot) wire to the service neutral will be some voltage above zero. Typically 120 volts in US residential dwellings.
*_


----------



## BillyD (Mar 15, 2008)

By the way Stubbie I read all your postings if I have time and I know you are a master. Thanks for all the time you spend helping us try to understand.


----------



## Stubbie (Jan 7, 2007)

Very good

Ok lets put it in a different perspective 3 wire feeders need bonding of neutral and ground at a sub-panel and 4 wire feeders do not. Forget about detached or attached.
Now consider a sub-panel and the path that current takes to get back to the transformer. Neutral current, another way of saying current on the grounded legs of a branch circuit (usually the white wires) flows to the neutral bar after it flows through the connected load on a branch circuit. From there it flows on the feeder neutral wire to the main panel neutral bar and then flows out on the service or utility neutral to the center tap of the transformer serving your home. Notice that I did not mention it flows to ground, because it does not, it flows to the source (transformer). These wires are current carriers (conductors).
Now consider the equipment ground in a 3 wire connected sub panel. It is not considered a current carrying wire unless a fault to ground occurs. If this type of event happens fault current travels on the equipment ground (bare wire in NM-b or romex) of the branch circuit to the neutral bar of the sub-panel. It then has to get back to the source (transformer) or the sub-panel breaker on the branch circuit where the fault exists will not trip out and clear the fault. Fault current on the equipment ground must use the *feeder neutral *wire to get back to the main panel and then to the transformer as no other path is available to it. If it can't get back to the center tap of the transformer then your branch breaker will not trip out and all metal likely to be energized from the fault will become energized to line voltage. 
It is because the *feeder neutral* is the only path available for *both* fault current and neutral or grounded leg current that we must bond the two in the sub-panel because only *one path* exists back to the main disconnect panel where we *always* bond neutral and ground because the only path back to the transformer is the service or utility neutral. The service to your house provided by the utility is always *3 wire* and we can never change this... so bonding of neutral and ground always occurs at the main disconnect panel.
So 3 wire feeders only have one path that current can utilize to return to the transformer and that is the grounded conductor or neutral wire in the feeders. So we have to connect neutral and ground at the main panel and sub-panels in order for both to utilize this path back to the transformer.

The draw back to this is the possibility of an open neutral event on the feeder to the sub-panel that will break this one and only path back to the transformer. If this occurs then fault currents if a fault should occur will not be able to get to the transformer and the fault cannot clear creating an electrocution hazard. I attached a diagram to show this below. 

On *4 wire* feeders we must* not *bond neutral and ground at the sub-panel because if we do then neutral current from our branch circuits will utilize *both *the feeder neutral and the feeder equipment ground to get back to the main panel and then to the source. Neutral current will take any path *available* to it to get to the transformer. We do not want any current on the equipment ground wire of branch circuits or feeders other than momentary fault currents to trip a breaker.

So now consider this *4 wire* feeder.... We do not connect or bond neutral and ground at the sub-panel. We provide a termination bar for the neutral wires or grounded legs which carry current in normal operation of the electrical system. We then provide a termination bar for the equipment grounds but we do not connect or bond it to the termination bar for the neutrals. Notice that a neutral bar is always on insulated standoffs from the metal of the sub-panel but the ground bar is bonded to the metal. In order to bond the neutral bar it to the equipment ground we must either install the main bonding jumper (usually a green screw) or a jumper to the metal can bonding it to the equipment ground bar via the metal of the sub-panel enclosure or some other listed connection.

Now consider the ground fault path. When a fault occurs the fault current flows to the *ground bar. *The equipment ground wire of the feeder from the main panel to the sub-panel is also connected to the ground bar in the sub-panel. The fault current flows on the *feeder* *equipment ground *back to the main panel where neutral and ground are bonded and then uses the service neutral (because of the bonding) to get back to the source. Remember no other path for neutral current is available line side of the main panel disconnect.

So on 4 wire feeders there is the possibility of *2 paths that neutral current may use to get back to the source*. We do not want it on but one path. So we remove any possibility for it to use the equipment ground of the feeder to get back to the source by not bonding the neutral bar to the equipment ground.

However with 4 wire feeders if we have an open neural event we have provided a path for *fault current* to use *other than *the neutral of the sub-panel feeder and we can still get a fault to clear.


----------



## Stubbie (Jan 7, 2007)

Hi again Billy

I located this graphic from Mike Holt to show the objectionable current if we were to bond at the subpanel or any panel served with 4 wires. Also be aware that metal conduit between panels may serve as the equipment ground instead of an individual wire as shown in Mikes graphic.

Another very important aspect is that with 4 wire feeders if we have an open neutral and because of the incorrect bonding as shown below the equipment ground of the feeder will begin carrying *all* the neutral current returning to the source from the sub-panel. This will mask the typical symptoms of an open neutral and we will never know that we have a potentially dangerous problem.


----------



## BillyD (Mar 15, 2008)

Hi Stubbie,
I believe it finally makes sense. I will continue studying the drawings. I want to thank (for all of us that uses the forum) you and all the pros and knowledgeable people on here that help. We know it takes valuable time away from your day to educate us. Again Thanks a lot.
BillyD


----------



## jrclen (Feb 20, 2008)

We should stop to think that not every location has adapted the 2008 NEC.


----------



## chris75 (Aug 25, 2007)

jrclen said:


> We should stop to think that not every location has adapted the 2008 NEC.



Yes, but I would rather just stop 3 wire feeders to outbuildings...


----------



## jrclen (Feb 20, 2008)

chris75 said:


> Yes, but I would rather just stop 3 wire feeders to outbuildings...


The code making panel is with you. I never saw any problem with it myself. I wonder when we will see 4 wire services on 240/120 resi.


----------



## chris75 (Aug 25, 2007)

jrclen said:


> I wonder when we will see 4 wire services on 240/120 resi.


Never will.


----------



## jrclen (Feb 20, 2008)

chris75 said:


> Never will.


That's what I said about garage and barn feeders. :laughing:


----------



## Stubbie (Jan 7, 2007)

Well if they ever do run 4 I bet they will be aluminum and not copper.....nooo.....they NEVER will be copper...anybody want to take that bet.....


----------



## HouseHelper (Mar 20, 2007)

Stubbie said:


> Well if they ever do run 4 I bet they will be aluminum and not copper.....nooo.....they NEVER will be copper...anybody want to take that bet.....


In our area we are seeing copper neutrals on the overhead drops, due to squirrels. They will chew the Al in half, but won't touch the copper.


----------



## Stubbie (Jan 7, 2007)

What is it they say....never say never.....:thumbsup:


----------



## chris75 (Aug 25, 2007)

jrclen said:


> That's what I said about garage and barn feeders. :laughing:


I use to pull 3 wires all the time, but that was really before I knew the code, used to pull phone and catv wires as well, then they would want a generator at the remote building, it just makes a real mess of things....


----------

