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How could this be wrong?


Kyle Kubs
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Ever see a panel that is just wired wrong, you've flagged a thousand of them in the past for the same thing but everything else is just so perfect that you start to doubt yourself? I was literally standing there wondering if I have hallucinated my way into the twilight zone.

The service drop hits the mast on a detached garage and drops into the main panel there. (see first picture) Just a few circuits for the garage and then THREE 4/0 aluminum lines go into PVC conduit, snake around the garage to the opposite corner, out the wall, down into the ground, about 50' across the yard and into and across the basement to the house panel (see picture 2) which is wired as a main panel with neutrals & grounds bonded on the bus bar and no ground path back to the main panel (fourth wire). - Ok this is an easy one... Fundamental... It has to have a four wire feed, But look at this panel, (flawless, work of art, this guy must have used a micormeter to space the wires equally) How can someone who does work like this screw up something so fundamental? And then there is a code inspection sticker on it... Am I losing my mind here? Have I finally breathed in too much funky crawlspace dust?

Then the water pipes are bonded to the basement panel and a GEC goes out the side wall and into the ground as if there is a ground rod there, I triple checked, it does not go back to the garage.

So, am I missing something? Is there some exception to the rule about subpanels that I am not aware of?

Ok, for whatever reason the pictures will not upload, but I think I have described it pretty well.

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. . . So, am I missing something? Is there some exception to the rule about subpanels that I am not aware of?

Perhaps. If there's no metallic path between the buildings, the house panel can be fed with three wires. The electricican can re-establish his ground/neutral connection at the house panel.

The four-wire feed is only required when there's a metallic path (other than the feeders themselves, of course).

- Jim Katen, Oregon

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Originally posted by Jim Katen

. . . So, am I missing something? Is there some exception to the rule about subpanels that I am not aware of?

Perhaps. If there's no metallic path between the buildings, the house panel can be fed with three wires. The electricican can re-establish his ground/neutral connection at the house panel.

The four-wire feed is only required when there's a metallic path (other than the feeders themselves, of course).

- Jim Katen, Oregon

I'm not sure what you mean about a metalic path. I think you may be confusing the fact that if there is a metallic path (rigid conduit, BX sheathing) then three wires are fine as the metal conduit will serve as the ground path bonding the panels & the grounds all the way back to the service panel.

Since the Neutral is a current carrying line it should not be bonded to enclosures once it leaves the service panel and must be isolated from ground conductors that will be bonded to things like the metal cabinets of appliances.

Ugg. Every time I try and visualize this parallel path thing my head starts spinning.

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Kyle,

I don't see anything wrong with set-up the way you describe it. The house is a separate structure from the garage and should have it's own grounding electrodes. With a three wire feed and no other mettalic path it would be correct to bond the grounds and neutral at the house panel. There is no "parallel path" with this. Ground faults at the house would be cleared at the house panel by tripping the breakers there because you are using the grounded (neutral) conductor to carry the current and not the grounding conductor. That part is the same as if you only had a single panel except, in this case, it is kind of waving hello as it passes the first panel.

Since the Neutral is a current carrying line it should not be bonded to enclosures once it leaves the service panel and must be isolated from ground conductors that will be bonded to things like the metal cabinets of appliances.

Not quite true in this case. There is an option here...See NEC 250.32(B) and then 250.32(B)(2)

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Yes to metal conduit (or a fourth, grounding wire, or even that fence if you had it attached to both panels(???)). IF you had a metallic path between the two panels, THEN you would have the parallel path for neutral current between the two panels (along the grounded conductor and the metallic path). In that case you don't bond at the second panel, BUT the separate house still needs it's own grounding electrodes.

I guess I'll repeat myself. I think your set-up is OK the way it is.

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Kyle,

Save the pictures as JPEG documents and resize them to less than 100 Kbs. Then, rename them so there are no symbols or spaces in the name. Something like Picture_1 or Picture1, but not Picture 1 or Picture (1) because anything with spaces or special symbols like partenthesis won't load. Then upload them.

If you're using netscape, wait until the box says that it's uploaded and then highlight and copy the code out of the upload box and paste it into your post and then click the submit button and it'll be there.

OT - OF!!!

M.

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Originally posted by Kyle Kubs

I did find the exception that Jim was talking about. What exactly consitutes a metallic path & why would it matter? Would this just be something like coduit or are we talking things like a metal fence or something?

Water pipe, gas pipe, phone line, CATV cable, metal reinforced concrete slabs, etc. Anything metal that might end up bonded to the grounding system at each building. Personally, I think a metal fence has an excellent chance of becoming bonded. I'd include it on the list.

- Jim Katen, Oregon

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Perhaps. If there's no metallic path between the buildings, the house panel can be fed with three wires. The electricican can re-establish his ground/neutral connection at the house panel.

The four-wire feed is only required when there's a metallic path (other than the feeders themselves, of course).

It's only required if there's an additional metal path. I believe it's always preferred, but it hasn't been that way in the past.

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I'll quote Mr. Hansen here. The underlining is mine.

Taken from Electrical Inspection of Existing Dwellings - 2001 Edition by Douglas Hansen, Casey and Kardon:

Separate buildings on the same property are often supplied by one electrical service. A common example is a house and a detached garage, or a separate "granny unit." When a separate building has more than one branch circuit, it requires its own grounding electrode [250-32a]. For purposes of this rule, a multi-wire circuit (two 120-volt hot wires sharing a neutral) is considered one circuit [225-30]. The same rules apply for this grounding electrode as for the one at the building with the service. Underground metal piping and foundation steel are required to be used, and if neither is available (or if only water piping is available) then a ground rod is also needed.

The subpanel in that second building should then have its enclosure connected to that grounding electrode. Doing so helps to assure that nay metal enclosures for electrical equipment at the second building will be at the earth potential of the building they sit on. It is not sufficient to have these enclosures at the potential of the building with the service. There can be a voltage potential of hundreds of thousands of volts across different points in the earth, and it would be dangerous to have electrical equipment at a different potential than the surface a person is standing upon.

The code allows a 3-wire feed to the separate building, using the neutral as the grounding conductor, ONLY when there are no other continuous conductive paths between the buildings. A conductive path could be a metal water piping, a concrete sidewalk, a metal fence, or even a telephone line. In practical terms then, a 4-wire feed is needed almost every time a sub-panel is installed in a second building.

Using a 4-wire feed avoids the problem of "objectionable currents" returning on the other continuous metal paths, such as water piping. By isolating the current-carrying neutral, no currents travel outside the feeder supplying the building.

In actual practice, most detached buildings are improperly grounded. The NEC was not nearly so clear on this issue until the 1999 edition, and there are many common misconceptions about grounding of separate buildings. Some jurisdictions even prohibit grounding electrodes at detached garages due to their misunderstandings of prior code editions. One part of the problem is that the NEC is giving one blanket rule that applies to large commercial facilities with multiple buildings from a common service, and also to residences. The importance of proper earth grounding might be quite different between those situations. The importance of keeping objectionable current off the grounding conductors remains the same however. The safest course is always to treat the subpanel in a detached building just like any other subpanel, with an isolated or "floating" neutral, and a bonded ground. The difference is that the ground bar also gets connected to an electrode.

Kyle,

Hope you've bought Doug's book. It always helps me clear the cobwebs, so to speak.

ONE TEAM - ONE FIGHT!!!

Mike

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Basically you can have a 3-wire setup to a detached garage lets say...BUT there must not be any metallic connection between the two....and it can be something a small as a telephone line, metal water pipes and so on. Even a concrete walkway with rebar between the two buildings is considered a path...and would require a 4 wire setup.

The 3 wire allowance is very specific............however what I have not seen mentioned here is even if the detached garage is a 3 or 4 wire setup....it still would require it's own grounding electrode......ie: ground rod at the detached building.

I disagree with Mr.Hanson's "Potential" concept....but it is needed for lightning and surge potentials.

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I ran some white romex to the barn, the 14-2 stuff so it will blend in with the snow and be easy to see when cutting the grass. Might even put one of them adapters on the plug, so I can plug it into the lampcord running down from the ceiling of my garage. It is about 300 foot, and there ain't no dead bodies or fire yet! The limitations are I can't run my 2hp compressor and welder at the same time, but "smokin and blowin" isn't my thing.

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Thanks Mike, That description was quite helpful in putting it in a way that I would absorb. I've thought about buying Mr. Hansens book several times but then decided to put my few spare dollars to other things, mostly because I have a really strong electrical background. When I was just 10 I used to spend my summers rewinding electrical motors and have wired residential houses many times since I was a kid as well as lots of 3 phase work. I guess I started taking the position like I had very little left to learn in that realm. Goes to prove there is always something left.

Seems something of a stupid exception though. Like the guy puting in a metal fence or a cable TV line at somepoint in the future is going to know to check and see if the whole electrical system now has to be modified... I made sure to explain in the report that as it currently exists it is fine but the future addition of any metallic path would require modifications that, in this case, would be substantial.

Jim - I hope you didn't take my reply to your first post as argumentative or anything of the like... Wasn't intended that way. - Six hours, one basement, 5 crawlspaces, two boilers, two water heaters, four electrical panels, 3 central air units, two attics and a pissed off realtor that didn't want to be there that long = spinning head at 11:00pm - Thanks for the help.

Since Mike went to the trouble of explaining what I was doing wrong I will post the pics just for the hell of it.

Really like the new look of the site Mike...

Oh and Les... If you coil up that 14-2 up and down your driveway on the way to the garage it works great for snow melt. No more shoveling![:-party]

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