I goofed...through a development of plans and intentions, I ran 3 wire service from the disconnect (on a pole) outside into a house (which started as a workshop...)


Because the meter and disconnect are on the pole, I need to wire the panel as a subpanel. But I ran only 2 hots and 1 neutral, no ground.


I have read in the 2000 NEC that it is allowable to have a 3 wire subpanel. I believe I need to drive ground rods at the subpanel and connect the neutral from the main to these rods.


Furthermore, it would be good to drive additional ground rods which I tie to my GROUNDS in the subpanel, which ARE isolated from the neutrals in the panel.


Therefore, there is no "loop" back to the main panel should my neutral ever be broken.


Is this correct?


It's about 170' from the disconnect and service entrance pole to the house. Everything is buried...in conduit, but I know I'll never get another line through the conduit. I could dig again and add the fourth wire, probably the BEST thing. Is it necessary?


Safety is the key, I agree.


Open to all comments and attacks...at least I am saying I goofed! LOL Thanks.

NO , Thats the way we are required to do it now here in fayetteville nc .
wayne

With only a 3 wire feeder the equipment grounding conductors must be bonded to the grounded conductor at the subpanel. If there is not a bond there is no fault clearing path.
Don

Bruce.

You are correct that if you follow a few rules you may run a 3 wire feeder in from the disconnect to the panel.

Here is the code article that allows this.


Section 2 of this is very important.


One thing is still wrong according to your post


This is wrong and dangerous, as you are feeding this panel without a grounding conductor you must bond the neutral bar to the enclosure just like it was a main panel.

You are correct that you need a grounding electrode.

When you are allowed to run a 3 wire feeder to a panel you must treat this panel as a service panel, the bonding the electrodes etc.

The way you have it set up a fault from hot to ground will not trip a breaker it will only feed current into one of your ground rods.

Feel free to ask more questions the members here will be glad to help.

Please read the code article I posted carefully and fully.

I have got to type faster, thank you Don.

Bob

Thanks for the reply.

So what you are saying iwire is that I treat the panel just like a normal "main" service panel. That's what I always intended...

Install my ground rods and tie them to the ground/neutral bus and also install the bonding screw into the panel.

Therefore, my neutrals and grounds ARE bonded in the panel, and I also have ground rods at the panel.

So, exactly as if the service is coming from the pole straight into the house, right?

And this is "OK" for me becuase I do not have any other metallic connection between the building with the disconnect (i.e. pole in my case) and the other building. Therefore, I do not have the possibility for the neutral current to be flowing through the ground wire...becuase there IS no ground wire OR other conducting pathway.

Correct?


Question related to your comment about current being dumped into the ground rods without blowing a breaker...Is this just becuase the resistence is high enough in the ground rods to not blow the breaker typically?

So does that mean that the ground wire would become energized? And then all the 4 wire applicance cases (fridge, stove, dryer, etc. would become HOT to the touch?)

So the neutral, which orignates from the center tap of the transformer, is clearly the "low impedance" return for the current to flow...and with the bonding screw, a fault would cause the breaker to pop becuase the low resistance would create a large current.

Correct?

So what happens if a neutral fails in a standard panel? Seems like the 240 stuff would work fine since they are balanced and the current would flow through the HOTs, but all the single line stuff would not work, as the neutral is not closing the circuit? But the ground rods to the panel, say, are still good...but the resistance is high...so the current is low...and with any load, the voltage will drop.

And that's what causes all the nightmares with neutral faults...some things work fine, some work to some degree, and some not at all.

EDITED: And now with the 4 wire installation of the 240 appliances, the shells of the appliances are tied to the ground, specifically NOT the neutral.

And the purpose of the ground rods is to ensure there is a lower resistance pathway from the ground (and also the bonded neutral) than through, say, me.

So the ground rods are purely a "safety" issue, always hopefully assuring a lower resistance pathway to ground than through a person.

BOTTOM LINE: I will check with my inspector and do what he says. It appears that I fit under this guideline. Wayne, I see you say it is NOT ALLOWED in NC, regardless. I'm in NY, FingerLakes area, so we shall see. Since I don't have any other metallic pathways, and hence (I think) the reasoning for 4 wires and no bonding in the panel (no potential for current flowing through ground), I guess I am no different than if the service came straight to me from the street.
Thanks again folks!


[This message has been edited by brucepirger (edited 11-17-2003).]

[This message has been edited by brucepirger (edited 11-17-2003).]

What am I missing here?

I can only think of this being allowed for a detatched accessory structure.

I think you'll have to dig and add an equipment grounding conductor, but I'm usually wrong when I argue Bob and Don.

Bruce you got it.

What was worrying me and I think Don too, was your statement that the neutrals and grounds where isolated from each other.

As to the tripping breaker and ground rods.

Say you have 25 ohms of resistance in your ground rod and you have a 120 volt fault to ground.

120 volts / 25 ohms = 4.8 amps

So you will not even be close to tripping even a 15 amp breaker.

Losing a neutral is a bad situation ground rod or not, a grounding connection to a water pipe in a neighborhood with all metal piping may help in that case.

Others can jump in here but from what I have learned the ground rod provides some measure of lighting protection.

But more importantly can help operate the utilities over current protection on the primary side of the transformer and help your electric equipment survive if a high voltage line was to break and land on the bare neutral / ground wire heading to your house.

At that voltage level 25 ohms is much more effective.

13,800 volts / 25 ohms = 552 amps much more than enough to open a POCO cut out.

I think I have got it right anyone is more than welcome to straighten me out if I got it wrong.



[This message has been edited by iwire (edited 11-17-2003).]

Hi Ryan, I see no reason the pole that this service starts at would not be the first "structure"

The article 100 definition of structure is pretty open.


Bob

[This message has been edited by iwire (edited 11-17-2003).]

Well, I wired the box with the grounds and neutrals isolated...but the bonding screw is in...and the ground rods are too.

If I have to dig and put in the 4th wire...then I remove the bonding screw and I am done. Viola.

If I can wire as a normal panel, than I am OK.

Is there a difference in safety? It seems to me, since there is no other possible conduction pathway from the main disconnect

(on a pole, 170' away, where someday I thought I'd build the real house, but live in the workshop for a few years first...but the workshop has become a mighty fine house over the past couple years...LOL)

then it seems that wiring as the "primary" panel is just fine. If there was another pathway, such as within the same structure, or metal water pipes, etc. then THAT changes everything.

I could never understand why I needed te subpanel...but now I think I do...and since I have no other electrical connections....I think I'm OK.

But the inspector will make the final say. I don't want to try and show him the NEC book and "force" my way. Not at all.

I never realized ground rods were more of a safety cushion...but now I understand. If their resistance is that high...they won't do much against the 120 fault...but a boatload against 4800KV!

Thanks folks.

I only picked 25 ohms as it is kind of a standard the NEC uses for ground rods.

As in one ground if not 25 ohms or less needs another ground rod added to it.

The grounds I have installed and tested have been more around 5 ohms.

Wouldn't a phone line or CATV line from that same pole to the house be another continuous metallic path?

Donnie

if memory serves street light poles once were in dispute , being in the structure realm and having to have disco's apply....

this could have been 225.32 ex 3's orgin

sure Donnie,
parrallel noodles are never discriminate

Guys
What is the difference if the meter is on the house or on a pedestal in the yard? The SE conductors only have to be 3 wire, (2 hots, 1 neutral). The meter is not considered service equipment, even if there is a disconnect at the meter pedestal, just a utility required measuring device. If you had the meter on the house fed via 3 wire from the pole, it would be a code compliant installation even when the TV & Tele underground wires are run in from the pole. So what changes when there is a meter in the middle of the yard? Nothing.
You could run a 4 wire feeder from the meter pedestal to the house, but it is not required. I have done it both ways. I prefer the feeder if money is not an object. Either method is fine as long as the neutral/ground issue is code compliant.

I do not think this changes anything here, the exception does not say a pole is not a structure.

The metallic paths have to be bonded at both structures or buildings to make this not possible.

It sure is something to think about, I do not see the cable TV line carrying much current for long.

Might make for bad reception.



[This message has been edited by iwire (edited 11-17-2003).]

Heres an article from this months IAEI Magazine addressing 3 wire vs. 4 wire feeders.

I'm sorry guys, but I think a pole is not a structure. A pole is neither built nor constructed. It is a tree minus the bark, and it is inserted into the earth. A garage is a structure. A house or building is a structure, a pole is not. Sorry.

I would require four wires to the structure. (the ONLY structure in this case )

Ryan,
I've built quite a few Service Poles! LOL

BTW. I vote for 4 wires. Pull the feeder out and repull it with a 4th wire.

[This message has been edited by txsparky (edited 11-17-2003).]

We have a little investor-owned utility out here in California called Pacific Gas & Electric. In more rural service areas, like the Sierra Nevada foothills, they often drop power to a customer-owned pole on the residential property, with a meter base and cutoff box (often a metermain panel) installed on the pole by the property owner.

The metermain is the service point, where the utility drop (or service lateral) neutral and the grounding electrode conductor are bonded. The pole is indeed a built object, in other words, a structure.

We run a three conductor feeder (2 hots & a neutral) to the house and treat the house panel as another "service" as far as system grounding configuration goes. We install a grounding electrode system (a Ufer in the foundation) at the house and bond the neutral and the grounding busses with an MBJ.

This is a major utility, and as far as I can see, it's a Code-compliant installation. I agree that if the phone co were to install their network interface device on the pole that's the point of service, you could have a metallic path between structures, and potential for a fault current on the phone line if a ground fault occurrs and the neutral of the feeder is compromised. This isn't an issue because the phone co runs their drop to the house itself.

Cliff

Ryan I am very interested in your logic here.

1)The code article in question says

"building or structure"

Why would they use the word structure if this was limited to buildings?

2)Electrical safety wise what is the difference?

How is this dangerous from a pole to a building but not from a building to building?

3)The pole did not grow there and have its bark stripped, workers brought it to the site and installed it.

The wires were attached to it, the meter base and disconnect where mounted to it.

It was constructed.

If you failed me on this I would have to go over your head. (Possible in this state, I do not know about yours)

You can only enforce the code, not what you prefer.

PS, I would prefer 4 wires too.

Bob


[This message has been edited by iwire (edited 11-18-2003).]

the pole/structure agruement did not originate with me guys, just thought i'd throw it in to spice it up here

most of you know that this thread can also venture down the 'why don't the poco just give us N-G isolation?' with interjections of seasonally acidic soil, aluminum siding, and NEC ref's re: the earth being unconductable


Steve, (aka Noodles~R~Us) sparky

[This message has been edited by sparky (edited 11-18-2003).]

Thanks for all the conversation fellas!

Let me throw in a few more details...I don't think they change anything.

The house sits 1000' off the roadway out in the boonies. Always wanted to build a log home out in the woods...I have the woods, the house is stick framed with log siding, hence the workshop idea initially (my kids will be too old I figure when I can afford to build what I want, so I best do something now!)

Anyways, I have a transformer sitting in the woods on a vault...from there the secondary service runs about 100' to a 6x6 (treated, so it's built! LOL) and plywood "panel". There's the meter, then a outdoor passthru panel. A 200A main breaker in that panel serves as the disconnect. From there, I ran the 3 wire feeder into the house (workshop). The idea was someday when I built the house, the "temporary" pole would be moved presumably into the real log house.

It was my understanding that I need only run the 3 wires into the workshop and treat it as the main panel, hence the 3 wire.

OK, there's no cable service out in the boonies...but Direct TV works just great (satellite).

There is a phone line that is in separate conduit down to the roadway...and the plan is indeed to mount the NIC (i think that's what it is called) on that same 6x6 pole.

That may change things...as it is a conductor...

If I ran the service straight from the transformer to the house (workshop), then I'd not have the disconnect on the pole, and I'd be just fine.

Everything is on and energized...I past my rough wire inspection with no questions.

BUT, I am uncertain as to whether the inspector really understands how things are. I told him I only ran 3 wires in and had ground rods at the panel in the house.

I don't care much about inspectors per se, I care about saftey. If there's a compelling safety reason to dig and run the fourth ground wire, I'm willing to pony up the cash and just do it. Yuck. If it is OK as is, then I'd obviously prefer to not sink in the cash.

Guess I should just get on the horn with the inspector and ask him specifically. But I do want to understand all that I can...and I'm not the type to listen to just one source. You folks are wonderful in all our your discussion, help, and information.

Thank you!

Bob, I notice that when I count the posts I've made on this site plus the other sites you and I frequent, there are well over 1,000 of them. The only reason I bring that up is that I hope by now you know that I NEVER make up the code as I go, and in fact people that do really anger me.

I would require the 4-wire service because in my opinion a pole is not a structure. I'm not saying that to be a PITA, I'm saying that because I am in the business of enforcing the law. 90.4 says that I can waive a specific requirement unless there is an alternative that provides an equal amount of safety. Is there? I don't know...I'm not as well versed in theory as I wish I were.

As far as going over my head, you certainly could, but my boss has never allowed it. In my city I am the highest authority in electrical. I would much rather discuss it with the installer and perhaps one of us could walk away a wiser man (probably me). There is seldom need to go over my head. I think I'm a reasonable enough guy.

[This message has been edited by Ryan_J (edited 11-18-2003).]

i would'nt sweat it brucepirger, we just love to split hairs here.

Ryan


I have great respect for you and have admired your insistence on following the letter of the code(s).

That is why I was surprised on your take on this.

I can not agree with you that a pole is not a structure, the NEC had to put an exception in for disconnects on light poles because they are structures. 225.32 exp. 3

Your friend Bob

Ryan,
If you would look at the code panel comments on the ROP that resulted in the exception that Bob referenced, you will find out that the CMP considered the light pole a structure. In my opinion the code supports a 3 wire feeder in this case.
How would the safety of the installation be changed if the pole was a very small building?
Don

Thanks guys, I'll look into that.

I followed txsparky's link and it was interesting, especially when they make it sound easy to add a EGC when it is not existing.


Problem solved

Well, if only it were that easy to pull in the ground wire...LOL...I'd do it.

Truth is, I passed my rough wire inspection about a year ago...not sure what that says about the inspector...but I have the sticker. So, I "could" just do nothing and have the final done and I suspect never worry about it again.

But I'm not the type to do that...and will bring it up with him, and see what he thinks. I have grown convinced there is no safety difference...so no real "need" to do this.

On that note, is it perhaps more dangerous? What if the ground wire on the 4 feed service were to break...then all my equipment grounds would be tied only to the ground rods...and then a hot fault to gnd would leave me in a bad situation. Would I ever notice a broken ground wire back to the main panel, until the hot to gnd fault?? I'm not sure I would.

If on the other hand a 3 wire neutral broke, I'd notice that very quickly, as nothing would be "right".

Isn't that correct?

Although I'm not justifying the 3 wire, although it does seem to make sense.

What's wrong with that "argument"??

Also, since the phone line is not connected to the grounding electrode of the electrical system (is it??), then I assume that is not an issue anyways.

Again, thanks for all the help gentlemen! I really appreciate the sounding board and all your time!

I don't intend to sound snotty here, but I suspect that it will come off that way, so apologies in advance:

It sure sounds to me like you've already convinced yourself to rip up the old 3 wire system and install a 4 wire system, and just want to be talked into spending the money

The reason that single phase sub-panels are normally wired using 4 wires (2 hots, neutral (or ground_ed_) , ground (or ground_ing_) ) is that if you were to connect the neutral and the ground at more than one location, a certain fraction of the neutral current would flow through the grounding system, eg. through your raceways and conduit connectors, etc. Inside a structure, this can pose a significant hazard. Even outside a structure it can pose a hazard, but it is generally not considered as much of a problem. In power distribution systems, the neutral is _regularly_ bonded to ground in multiple locations, in other words following the exact opposite rule (in your house you bond neutral to ground _once_ and only _once_, but the POCO bonds neutral to ground many, many times).

In the situation that you face, you are halfway between service in your own house and power distribution. You have two separate 'structures', or perhaps a structure and a pole (I'll let the higher ups make that call). You _don't_ have any other metallic pathways between these two 'structures', so the three wire system is possibly allowed, and would be very much like the three wire service that the POCO normally provides.

Given the choice, I personally would prefer the three wire system. My reasoning is that I would prefer to have the electrical system tied to ground in my house, rather than tied to ground at a point more than a hundred feet from my house. The longer the run to the bond between the neutral and the ground, the greater the impedance, and the greater the possible voltage difference between the electrical system and the building ground. In terms of safety issues, I believe that you are at the point of '6 of one, half a dozen of the other'; by not having the alternate metallic pathway between the two 'structures', you have eliminated the major safety issue of tying ground to neutral and multiple points, so now you have to balance the remaining safety issues of having neutral and ground tied in two locations versus the safety issues of having a much longer run to your neutral to ground bond.

I suppose that you could eliminate the 'where to ground' issue entirely by using a transformer. You would re-derive the neutral in your house, and bond it to your grounding system there. Seems like a pointless exercise to me, but I believe that it would be legal....

-Jon
I personally would prefer the thr

Well, I'd just assume leave it 3 wire...a whole lot easier and cheaper! I can buy each argument, but lean towards the 3 wire myself.

I'll do whatever my local inspector requires. I like having the bond in my box inside the house too...not 170' away.