Conduit Fill

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John,

It would appear that you've bought a couple of the most insidious myths about electricity. These are things that sound reasonable, that we've been taught over the years as part of 'common sense' or 'conventional wisdom', and which are outright _wrong_. This is not to cast any sort of aspersions on you; we've all been there, and had to unlearn these things.

1) Electricity follows the path of least resistance. This statement is strictly true to the point of being misleading. The reality is that electricity follows _all_ paths available to it, in inverse proportion to the resistance. This includes the 'path of least resistance', but it also includes the high resistance parallel path.

2) Electricity tries to get to ground, or a ground rod is a safe place for electrons to go. The reality is that electric current always flows in a closed circuit path, and always 'trying' to find a path back to the source. The 'source' is usually a transformer. Soil is entirely irrelevant to this truth. For reasons of safety, we _bond_ all non-current-carrying conductive material back to the source, and electrically connect it to one of the source terminals. The Earth is simply another chunk of conductive material that we need to bond.

In the event of a short circuit at the range (I presume hot to frame, 4 wire circuit), current will flow from the transformer along one of the 'hot' conductors, through the main breaker, down the bus bars to the branch circuit breaker, through the branch circuit hot to the range frame to the branch circuit EGC, back to the panel, through the 'main bond', and then through the grounded conductor back to the transformer. Additionally, since there is a grounding electrode at the transformer, and grounding electrodes at the panel, some portion of the current will follow the parallel path through all of your grounding electrodes, into the Earth, and back to the transformer. But the bulk of the current will follow the copper wire path. The only breakers that could trip in this case are the ones in the path of the current, and the grounding electrodes at the outbuilding are irrelevant to this.

-Jon
 
Winnie, That was a very good class on electricity. And I appreciate the time you took to teach it.
In response to the ground rod situation discussed earlier, here is what the inspector emailed me today.
"Tell your friends the AHJ is never wrong. I have exhaustively investigated this since we have had deaths in the past. I don’t think we will ever be able to account for all stray voltage on Lake Keowee, however I won’t add to the problem. Nec 555.15 would apply".
 
Quote ""Tell your friends the AHJ is never wrong."

Apparently, he has never met an AHJ on a military base. Not to slam base inspectors, but have run into plenty who's entire electrical experience has been plugging their Nintendos into the receptacle outlet. And they would come up with some really fantastic "code" for me to follow.
 
Grounding

To ground wiring and equipment within the scope of Article 555, follow the specifications in Article 250 and 555.15(A) through 555.15(E).

You must connect the following items to an equipment grounding conductor run with the circuit conductors in the same raceway, cable, or trench:

(1) Metal boxes, metal cabinets, and all other metal enclosures

(2) Metal frames of utilization equipment

(3) Grounding terminals of grounding-type receptacles

The equipment grounding conductor (EGC) must be an insulated copper conductor with a continuous outer finish that is either green or green with one or more yellow stripes. For conductors larger than 6 AWG, or where you use multiconductor cables, you may re-identify conductors as allowed in 250.119(A)(2)(b) and (A)(2)(c) or 250.119(B)(2) and (B)(3). Size your EGC per 250.122—but not smaller than 12 AWG.

You must terminate the EGC for branch circuits at a grounding terminal in a remote panelboard or the grounding terminal in the main service equipment. Where a feeder supplies a remote panelboard, run an insulated EGC from a grounding terminal in the service equipment to a grounding terminal in the remote panelboard.

This is from Mike Holt's Newsletter
 
John,

You are welcome.

You should invite your inspector to join the forum, we all have stuff to learn, and I learn here every day.

It sounds to me like your inspector is bringing up a very real issue, one that is outside of the scope of the NEC, and one that _potentially_ (pun not intended) would be exacerbated by an NEC compliant installation. The ground rods at the outbuilding are _required_ by the NEC.

However if the local authority is dealing with stray voltage issues on the lake, then they may be loath to put more grounding electrodes near the lake. Since stray voltage is so hard to pin down, there may be no rational basis for such prohibition, but simply the hunch of the guy dealing with the mess.

Additionally, the ground rods themselves are probably of very little safety benefit. I personally wouldn't fight it if the inspector were to prohibit a couple of ground rods at an outbuilding. What is far more important is the proper bonding of any metal structural elements or pipes, so that a fault to one of these items will trip a breaker rather than leaving it energized.

If these structural elements are in contact with the earth, in particular if there is bonded rebar in a foundation, then you already have a grounding electrode weather you want one or not, and such bonding _is_ a real safety issue. If your inspector were to prohibit bonding of these structural elements, then I would fight it, because that is a real safety issue.

-Jon
 
John, Winnie has covered the myths you were believing in, which is why I asked you the questions in my earlier post, so I won't go there.

I will however make the statement that this Inspector you are dealing with is wrong period. It appears as though there might also be some confusion in the difference between a GEC and an EGC as well as the differences in the functions they perform.

Roger
 
Winnie, You are very knowledgeable. Thanks for your feedback. You should be teaching code/technical classes.
I am glad the inspector finally used article 555 to make his point. He also told me that there have been fatalities on this lake, due to the common grounding practice. Can you believe an inspector would even take the time to email back and forth to assist me with the particulars. I sure am glad I found this forum. It has been so helpful.
You see, I got my masters many years ago. I am retired/disabled from industrial electronics and electrical in manufacturing facilities for most of my career. When I took the masters test I was in construction. Since I have been out of work I also got my mechanical (EL) license too. Since the board that accredited me with my masters reciprocated with the Contractors board, it was just a matter of a check and business ethics test. So you can see why I am not up to speed like the rest of you guys and girls.
My real strengths are ac & dc drives, controls, and system design for industry. Never in this field, did I ever see an inspector. And as you can see I had a free hand in most everything I built or installed. But now I want to learn the in's and out's of the construction business. I want to to this type of work part time to supplement my meeger income.
 
roger said:
John, Winnie has covered the myths you were believing in, which is why I asked you the questions in my earlier post, so I won't go there.

I will however make the statement that this Inspector you are dealing with is wrong period. It appears as though there might also be some confusion in the difference between a GEC and an EGC as well as the differences in the functions they perform.

Roger
Click to expand...
Roger, right or wrong he (inspector) has reason's for his requirements. See Winnies post and article 555. I am not going to argue this point with you or the inspector. The AHJ has the final say when all is said and done. Would you do any work that has already been decided by the AHJ, just to undo it? I thinks it's time we put this matter to rest.
 
John, 555.15 is not debatable, it must be adhered to, the problem is, it has nothing to do with a Grounding Electrode.

Roger
 
John, if this inspector told you that you don't have to use GFCI's for places they are required would you follow his lead on that too?

The reality is that if anything does happen to some one or property, and a deficiency is found as far as a code requirement is concerned whether it contributed to the problem or not, you will be liable even if it is shared with the inspector.

Roger
 
John,

One more thing you may want to read is 555.1 , the last paragraph states

that this article is not for privite, noncommercial,owner or resident single

family dwellings. FWIW.
 
benaround, In certain circumstances the AHJ has the authority to make exceptions. This is an instance where this AHJ has studied this in detail due to a death on this lake in 2004. And several over the last 10 years. Now, I do not know exactly what their findings were, but I am not going to argue this with them or you. Understand, I planned to use two electrodes when I planned this project. They told me NO!!!!!!
 
It would be interesting to know what is causing the stray voltage, probably improperly wired ship to shore cords. I think we can safely rule out noncurrent carrying conductors connected to the earth.
 
Stray voltage is all about current flowing where it isn't expected.

I certainly do not know all of the possible sources, nor all of the ways that things can break to cause stray voltage.

If you have an installation that is compliant with the NEC, then you will have electrodes in the soil bonded to the service neutral. This is further connected to both the secondary neutral of the service transformer, and to the grounded leg of the _primary_ distribution circuit. The primary distribution circuit is almost certainly 'multi-grounded', meaning that the grounded current carrying conductor is connected to earth via a grounding electrode over and over again.

This means that distribution return current will find a parallel path through the earth.

Take a look at this thread for a related discussion: http://mikeholt.com/code_forum/showthread.php?t=78799

One of the solutions used for stray voltage (not one that I am advocating, simply reporting) is to break the direct connection between primary neutral leg and secondary neutral at the service transformer. The primary neutral is still grounded, and the secondary neutral is still grounded, but the metallic bond between the two is removed. Of course, the most common causes of stray voltage are probably real wiring faults, but even after you eliminate all of the wiring faults, you can still have real problems with the stray voltage.

-Jon
 
John,


I'm just giving you some info that I thought you would be interested in.

John, don't take offence from any of this, If we didn't care we would not

even respond.
 
benaround, I understand, and I appreciate feedback, negative or postive. Thats how we learn. I am not offended. I respect what all of you have to say. THANKS TO EVERYONE.
 
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