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Post by northernfarmer on Mar 13, 2022 11:51:22 GMT -6
I don't believe there is a thread on farm yard electrical questions and information so made sense to start one.
I have a question that relates to neutral to ground bonding within breaker panels on the farm down stream from the tranformer/meter/main breaker for the yard ( some may have more then one transformer or more then one meter and main breaker system in a yard ). I am honestly not sure if the first breaker panel being fed from the meter/main breaker is to be bonded or not to be bonded. I believe in situations in city wiring where the first breaker/shutoff is the actual main breaker panel in a house, its to be bonded from neutral to ground, then if a sub panel was placed in a built on garage for example and a breaker from the main house panel powered that sub panel, then that sub panel is NOT to be bonded internally and instead a fourth wire ( ground wire ) ran from the sub panel to the main panel.
I just don't know if in a farm yard situation with that main breaker within the meter housing at the transformer location, if that is the bonded location and therefore no other electrical panels in the yard should be bonded ?. Bonding where one should not can cause returning electricity to feed into the ground rod or any metal connecting structures trying to make its way back the the source of power as in theory no power should be on a ground wire. Yet if a breaker panel is supposed to be bonded and is not, can cause breakers not to trip when they should is my understanding.
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Post by kenmb on Mar 13, 2022 15:55:28 GMT -6
This is where the code book comes in as I have to go from memory. I think my memory is still good on this but as always, I will post to steer guys in the direction for them to pursue the subject further rather than take my words as fact and 100% correct.
I believe you have it correct NF. Only the main service has the neutral and ground tied together. It doesn't matter if it is a farm, house in city, apartment building with sub panels everywhere, or industrial site. Any time the voltage is changed you have a new main service on that feed and so the ground to neutral bond is done accordingly.
On industrial sites it is more important as we have ground fault protection to be detected as it travels in a neutral or bypasses and travels through ground. The neutral and ground being seperate is important for this protection to operate. In a city house or farm there is no ground fault protection so I beleive it comes down to a safety issue.
The safety issue is that a ground fault could be a few hundred amps. If that flows through a wire with 0. 5 ohm total resistance then 100 amps at 0.5 ohms is 50v (v = I x r). So if your ground and neutral is bonded at the sub panel then that ground current is flowing to the neutral but more importantly, if there is a 50v potential created in the ground fault then that is now being applied to the neutral circuits. So instead of a person in contact with something that should be at 0v it could be at 50v. And since all your metal stuff is supposed to be at 0 v but is now at 50v then metal conduit, metal light switch covers, metal enclosures all become a hazard.
In reality 0.5 ohm resistance is very unrealistic in a system with many ground paths but the code book is not about what is most likely, but rather based on a very specific (ie rare) combination of circumstances suddenly being deadly.
I expect you will find many, many sub panels with the neutral and ground tied together. And I doubt they will ever be a hazard to anyone. But then again, ground faults have killed people and that is not rare. I remember a news story from about maybe 10 years ago from nearby where a guy, I think grain bin crew, was killed connecting up to a farmer supplied temporary power panel and grounding wasn't right.
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Post by kenmb on Mar 13, 2022 16:16:49 GMT -6
To make it a bit more clear, if done properly, ground current flows back to source at main panel via a dedicated ground wire so if there is a 50v drop in the ground circuit then it is across the ground wire and not the neutral. However, if your sub panel has the ground and neutral connected together then the ground current now also flows back to the main panel through both the neutral and ground. If this circuit back to the main panel had 50v due to 0.5 ohm resistance at 100A then the neutral at the sub panel would be at 50v and all other neutrals connected to that sub panel.
Ground current/voltage discussion generally needs good drawings to really understand as I may not be saying it correctly here.
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Post by northernfarmer on Mar 13, 2022 18:26:55 GMT -6
I wonder if I would be able to visually find where on the transformer pole that the neutral tap on the transformer is indeed bonded to ground and as I think of this and could be wrong, possibly the steel rod or whatever they drive into the ground as the guy wire for the tension on the pole from the weight of the high voltage lines, if that steel cable and rod would be the neutral to ground bonding and not sure if there is a rod also driven in near the pole itself. I suspect inside the cover below the meter where the main breaker is I may not find any ground to neutral bond there but should investigate that as well.
For sure in this yard there is no separate grounding wire either overhead nor underground coming from the transformer pole to any building, its the traditional two hots and the neutral, and ground rods as per code at each building or splitter box location.
My former thinking in terms of each breaker box first in line from the transformer was the actual first disconnect and therefore to have neutral bonded to ground but I think that has been mistaken thinking all along and in part because of what I noted an electrician had done in one location and thought of course that it was correct, I have a feeling he goofed and was thinking in terms of the breaker box being the first disconnect. I have what amounts to three different power feeds that come off of the main transformer meter, one overhead and two underground. Two of those power feeds across the yard ( one power feed constituting of two 120 volt lines and a neutral in my non electrician language ) have power branched off of them in two or more locations by means of splitter boxes but no disconnect means within that length of main power feed, only at the end of each branched off line which terminates at a breaker box.
So in theory with this scenario Ken, I should only find a neutral to ground bonding situation at the main transformer pole that has the main breaker for the whole yard at that location and no bonding anywhere in any splitter box nor any breaker panel on the yard.
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Post by torriem on Mar 13, 2022 19:30:10 GMT -6
I'm not sure that's right. The breaker on my pole goes to the generator switching panel first, and surely the ground bond is in there, else when the generator is running there's no bond at all.
My yard wiring dates back many years and I have three subpanels (my house, a shop, and some grain bins) fed by only 2-conductor cables sheathed in a copper ground. not sure why the electricians did it that way. I guess the thought was if you bond a ground wire at the house with this copper sheath, and another ground rod at the main panel that would be enough unless you dug out the ground rod or plane and got shocked by it (as you surely would).
Also a lot of rural services in my area are fed by a single wire with ground return. I've often thought that is pretty dangerous if you hit a pole with a vehicle or machine and broke that ground wire somehow. I know they typically run a ground/return wire along the poles these days when new lines go in. But somewhere it has to do a ground return if you only use one of the three phases.
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Post by northernfarmer on Mar 13, 2022 20:34:42 GMT -6
I could be entirely off in my thinking, that is why my posing the question and then laying out how I "think" it is but I should clarify that I am just not sure and why I thought a thread like this might steer me and others in the right direction on a variety of electrical questions. Too bad the electrician who had come onto the other site for a bit isn't around and still wonder why a very few members took it upon themselves to treat him like total dog crap, I was floored by it and of course he had enough of that shit and left. Some questions were raised or perhaps more so stated about what they were planning to do on their yards and his answers were not what they wanted to hear and so the insults flew. Not planning on re creating that here LOL.
When I get a chance sometime I hope to have a chat with a certain electrician to see if he is familiar with farm systems, not all electricians are going to know a farm setup would be my guess.
Torriem, I could be thinking of another type of underground power cable then you are speaking of but what is very common to farm yards with single phase is this USEB-90 cable which consists of two aluminum conductors and often times what they call a "reduced neutral" which I believe is rated at 70 % capacity of the aluminum wires and is copper stranding that encapsulates the two insulated conductors. The reduced neutral is still to code and you guessed it, cheaper because it contains less copper then if it too had a 100% rating of the power cables. That copper portion of the cable is used as a neutral wire, it is not used as a grounding wire or at least not with any 240 volt breaker panel with two 120 volt lines with 120 volt breakers and 240 breakers as a mix as a house or shop would have as its carrying the uneven portion of the load back to the source. Of course say it was a 240 volt aeration motor being run, no current returning should be present on the neutral in that instance.
Overhead wire for most farms in the past is really no different, the two triplex overhead style power cables are insulated and the third bare cable that supports the weight of the triplex is the neutral wire.
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Post by torriem on Mar 13, 2022 20:59:03 GMT -6
Yes that sounds like the cable that's used here. My house doesn't even have ground wires in it!
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Post by northernfarmer on Mar 13, 2022 21:31:26 GMT -6
Yes that sounds like the cable that's used here. My house doesn't even have ground wires in it!
Depending on where the breaker panel is located and how accessible it is to routing a wire directly from the outside through the wall, no doubt a ground could be installed, would have to be careful depending on what is underground if one was driving a ground rod into the ground, any electrical, gas line, sewer line, weeping tile etc that was underground. Then again you seem like a well grounded person, that's probably good enough and to code right there
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Post by kenmb on Mar 14, 2022 8:47:18 GMT -6
I was pulling an old overhead feeder off my pole in fall and how that was done was there was a ground wire running down the pole from the transformer tank and into a ground wire and the ground/neutral of that overhead three conductor line was tied to that ground. I beleive code is that the ground (doubles as neutral) needs to be only sized for 60% of phase current. There is a fair amount written in code books about reduced neutral feeds. I beleive it hinges on the idea that one would exercise the idea of balanced phase loading so that reduces the current flowing in the neutral. Current in phase 1 at 120v to neutral at 100a is 180 deg out of phase with current in phase 2 so if phase 2 is at 120v and 50a then what you have is the neutral current being actually 100a - 50a = 50a. Now, if you ran a 200a feed with 150a neutral and put a full 200a load on at 120v and 0a on the other leg then your neutral current would be overloaded because it is at 200a. I guess the people who write the code expect no one to actually do this. As for the electrician on the other forum I believe he is the guy who said he worked at a potash mine. If so, yes, I liked reading his posts and would take what he wrote about things over what I am saying about these matters. I think he had a good understanding of how things were done. As for the overhead line. The way I understand it is based on node theory. If you ground the neutral at the main panel then that is no different than having it grounded at the sub panel. Meaning there is no advantage to running a seperate ground cable and neutral cable back to the main panel if node 1 = node 2. If you draw a schematic, making multiple connections to the same wire is considered all the same node. Regardless if there is 300 feet of distance between one connection and the other. In the picture node 1 and node 2 are basically the same points. You can consider them 6" apart or 500ft apart. You would not run a seperate wire for 6" so therefore don't need a seperate one for 500 ft. So no point running a seperate neutral from sub panel A back to node 1 given that the enclosure of sub A is effectivelythe the same as node 1.
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Post by northernfarmer on Mar 14, 2022 9:47:08 GMT -6
Speaking of creating a good ground as per often the use of a ground rod driven 8 feet into the ground in area's that are clay which I would guess a lot of places within western Canada on farms would fall into that category, in reading about ground effectiveness depending on soil moisture content or if frost is involved it states that frozen ground increases resistance sharply and why ground rods should be driven in well below frost line. Also soil type and moisture content as below 10% moisture the resistance increases sharply there as well. The articles examples of having solid rock or in the case of Hawaii with volcanic ash contain almost no moisture. I can see where in some locations that a ground wire would have to be ran back to the source just to create an effective ground. I've also seen drawings of laying a rod or steel plate horizontally in a trench but not all that deep into the ground and can see that would not work during the winter time in our Canadian climate, but would more then likely work fine in the southern states or Australia. That poses the question as to how that works out in places that are very rocky as to the effectiveness of the ground rod at a transformer pole or ground surface mounted transformer, how anything can be properly grounded to earth.
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Post by kenmb on Mar 14, 2022 13:13:27 GMT -6
I have done ground grid testing and ground rod testing as part of my old career. Even did the design work for a power system up north with only bedrock but the actual ground design I contracted an engineer who specialized in this stuff. Ground rounds in rock are done by boring a hole about 10" diameter, setting the ground rod in and cementing with a specific concrete that is conductive so instead of that 2"or so circumference ground rod contacting disturbed bed rock now becomes +30" so lower resistance. Rock isn't the best conductor but if you have one massive stone the size of a football field then it can radiate energy due to its large area. I was never aware of ground plates till about 15 years ago. I don't know how long they were accepted before then as I didn't do anything with residential kind of systems. The last panel I put in on the farmhas a ground plate as I found that much easier to install than a ground rod. I already had the trench for the cable so dropping a plate in was simple. The idea of frozen ground isn't something I thought of or crossed my mind. We told clients we couldn't test systems in the winter because our test rods would be ineffective in frozen ground but never thought about how that effects in service grounding. Perhaps during a ground fault you would have lots of current and heat thus thawing that ground instantly and creating the water needed to provide good contact. I don't have a copy of the CEC Rule Book anymore but suspect ground plates are only allowed for low energy systems. The residential and farm systems we are talking about are quite forgiving. A 100A 240 service is a very different thing when something goes wrong compared to a 600v 1200A or much larger. Yet the code book will often treat things similar or provide different rules for systems based on voltage level or short circuit current capability, and likely a few other parameters come into play. I really don't think a guy would run into an actual safety issue having a ground and neutral connected in a sub panel on a farm. Theoretically the hazard must exist and therefore the rules, but to actually present a hazard then likely not. Ungrounded systems or a damaged ground likely is where most safety issues lie vs having a very good ground and very good neutral but incorrectly tieing them together. When I do stuff around the farm I pay attention to grounds above all. If a good ground is in place then I would say 99% of hazards are eliminated. At work I can say everything that blows up brings the ground system and ground protection scheme into play above all else and if something isnt right in how this grounding all plays out it is the difference between cleaning up carbon and putting a system on line in a few hours vs replacing an entire piece of gear or building. My old computers have pictures in buildings totally burnt out because the ground fault system didn't work. And lots of switch gear on sites turned to molten metal. Yes, I fixed lots of stuff over the years. I looked for some articles about connecting ground to neutral but the ones I came across don't go into specifics. Probably the best resource for talking electrical code is the electrical Handbook (not code book). I used to have this one my desk also and it is very good. The size of a dictionary at around 700 pages at 8.5 x 11" with lots of drawings. Where the code book leaves you scratching your head why the code is there, the Handbook goes into depth why. If you find an electrician that knows of it, and more importantly - uses it, then he is a guy I would trust and take his word on something. webstore.ansi.org/Standards/CSA/CSAC221HB2021
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Post by northernfarmer on Mar 14, 2022 14:53:04 GMT -6
I believe I found a freebie for that electrical handbook, a pdf download.
I imagine that each wired scenario in a farm yard or similar with the relatively low voltage and amperage would dictate how counter productive bonding the ground to neutral at a sub panel would be ( sub panel being every panel in the yard after the meter breaker ) . I know quite a few years ago a little experimenting was being done using an aeration fan to test the amperage it would draw and possibly during that experiment the amperage was tested at the ground rod and there was some current travelling into the ground and never did discover what was the cause of it. Some years later damage was discovered and repaired on an overhead line that feeds that underground portion of that system, I have not tried testing the ground since then, I know one of the legs of power was compromised as well as the neutral and perhaps uneven voltage under load between the two 120 volt legs would cause a resistance imbalance and with a poor neutral to compound matters give the ground far away from the power source the reason to have some current flow into the earth rod, I did not think that panel was bonded and an item to inspect now that I think about it. Strange things happen when a leg of power or a neutral have a bad connection or damaged wire as per another situation I finally sorted out as per an overhead neutral having broken most of its wires within its wedge clamp that strung the triplex. What I am getting to is that if a sub panel is bonded that should not be, that would somewhat mask the actual problem and force current into the earth because of a damaged neutral system, not the ideal situation.
That is interesting about the solid rock earthing method, makes sense and to get a rod into the rock regardless. That becomes one expensive ground rod, drilling into bedrock !.
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Post by meskie on Mar 14, 2022 16:29:59 GMT -6
Around our barn yard we have trouble putting a ground rod in more then a couple of feet before we hit rocks. So I can’t imagine trying to put one in through bedrock.
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Post by kevlar on Mar 14, 2022 17:42:03 GMT -6
Actually that’s probably easier, you can drill into bedrock, stones you can’t.
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Post by kenmb on Mar 15, 2022 7:32:51 GMT -6
Tha link goes directly to the Code book, and the Handbook is there on the left side. I really hate pdf especially for something 700 pages long and technical research related. I don't know if it is just me and my age but I would rather pay for a paper copy. But for quick research that pdf Handbook is certainly something a guy can make use of.
Sections 8 or 10 cover grounding so a guy could look up what the restrictions are for where a ground plate can be used. As Meskie says, ground rods are not always a simple job to install but a plate definitely is.
I had a problem on an overhead line about 10 years ago with a bad neutral/ground connection at a tap to an old barn and the line went on to the house. Whenever the pressure system or other large single phase load cut in the house some lights got visibly brighter and other things dim. It was a connection on that overhead ground. So I suspect one reason the code allows this type of 3 conductor feed off the main panel is that if you ever develop problems with a bad connection and therefore compromising your ground return, then it will become evident as did I experience. Think of it as a self monitoring arrangement. Some of the code rules are written using that kind of logic. There are some really bizzare rules in the Code book but the Handbook does a really good job of explaining them.
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