Here is a question about outbuilding grounding.
Two outbuildings will eventually get their power from the service panel in the main house. Right now, only one does. It gets a 240 feed on the old 3-wire plan. A second building is to be added. This is a horse barn (no concrete stall floors), which will get a 30 amp 240 feed from the sub panel in he second building.
Both buildings are at some distance from the house and have no metallic connections to the house other than the power feeder.
In order to safely ground this, I think I understand that today’s requirement is for a 4-wire system. The question is, where other than the main service panel in the house do the third wire and he equipment ground connect to one another?
Also, I am informed there can be no ground rods at the barn. Should there be ground rods at the first outbuilding (there aren’t today)
Joe
Replies
Hey Joe,
Right you are, the 2008 NEC says any feeder to a panel in a separate structure must be 4-wire (2 hots, neutral, equipment ground).
If your jurisdiction has adopted the '08 Code, the building that has power now is grandfathered...a three wire feeder is OK, no equipment grounding conductor, as long as, as you're aware, there is no metallic path between the structures (other than the feeder conductors).
But the Code requires (and has for many many years) that there be a grounding electrode at the second structure. This is basically a lightning drain. And the neutrals are bonded (electrically conected) to ground. You do that with a bonding jumper--a screw or a bit of heavy wire that connnects the neutral terminal bus to the grounding bus.
Now, about the new subpanel, fed from the existing subpanel. If you're under the '08 NEC, you'll have to run a 4-wire from the existing subpanel to the new sub. If under an earlier edition of the Code, a 3-wire ought to do it. That's assuming that your AHJ has no additional requirements.
I'd like to know who says you can't put a ground rod in at a horse barn. You have to for lightning safety. A lightning strike can impress a large energy pulse in underground conductors, and when that gets ot the subpanel, you want the can (housing) well-earthed, so that the pulse can drain off to ground (it'll arc to the can from the hots or neutral--makes a real mess of things, but preferable to having all that energy go right into the branch circuit wiring).
Be careful around buildings with livestock. It's much better to run a 4-wire feeder to any sub in a barn or stable--with an equipment grounding conductor (EGC) in the feeder, any fault current at the barn will return to the feeder panel on the EGC. Without the EGC, the fault current goes to ground at the grounding electrode, and the feeder breaker won't trip. With an EGC, if the fault current is sufficient, the breaker will trip.
With livestock, the fault current going to ground will create a voltage gradient radiating out from the ground rod. In the wrong conditions, a horse or cow will get a shock because it's forefeet and hind feet are far enough apart to produce a voltage gradient. The animals will act skittish, and often for horse, won't drink.
Ranch or farm wiring is full of little oddities like this. The wiring will work, but stuff is going on that isn't good, or one fault will endanger the health of the stock.
If I was you, I'd pull an EGC from the service to the first structure, and use a 4-wire to the second.
If this is impossible, I'd set up a fault monitoring program for the first subpanel--at least monthly, turn on all the lights and appliances, and heaters, in the barn, and measure the current in the grounding electrode conductor (wire from the ground or ground/neutral bar to the grounding electrode), using a clamp-on microammeter. If there's any current (more than a few mA), look for a fault.
Good luck,
Cliff
"at least monthly, turn on all the lights and appliances, and heaters, in the barn, and measure the current in the grounding electrode conductor (wire from the ground or ground/neutral bar to the grounding electrode),"Instead of all, don't you want to get the maximum unbalanced load?.
William the Geezer, the sequel to Billy the Kid - Shoe
Bill, you're looking for a fault--ground fault, to be exact. You want everything on, so that a little leakage here and a little leakage there (high-Z faults) will add up and be readable by an amp-clamp.
An amp-clamp that'll read 0.1 amp or less is the tool you need. The Fluke 322 is a reasonably-priced amp clamp (for a Fluke), and has both a 0-400 amp range, and a 0-40 amp range with 0.01 amp resolution.
I've caught several ground faults using an amp-clamp....I learned first hand that you have to be extremely careful when making test measurements, not make any assumptions. Opened up a baseboard heater once to troubleshoot, ultimatley found about an amp of ground fault current in the EGC.
Cliff
Cap:Out here in the county, we don't have inspectors or a code, but I like to be safe anyway. My reason for worry about the ground at the barn was the whole animal shock/equipotential plain issue. I really don't have a good technical grasp of that. However, I was warned that animals were affected or even electrocuted in cases where the neutral was re-grounded at the barn and something went wrong. I think this is worse in barns with concrete floors (my stalls have non-conducting polyvinyl acetate mats), but even so, why take the chance? Who knows what we might change in the future?I am working this in two stages. Stage one is to get the power to the barn, and stage two (a much bigger pain) will be to rewire back to the main service panel in the house.So, as I understand things in light of your comments, I start with a grounding electrode at the existing outbuilding with power, to which the existing neutral bus is bonded. SO far so good. I have the electrodes and some #4 bare copper, and will use Cadwelds.I then run four wires to the barn, two hot, a "neutral" and the ECG. The neutral and ECG both come off the neutral bus in the existing powered outbuilding. Both are bonded to the neutral bus in the barn. The neutral bus in the barn is bonded to a grounding electrode. Is this right?So, in effect, the ECG is just a redundant neutral?Then, when I get to phase two, I run a new ECG from the neutral bus in building two, straight back to the main service panel in the house?
That main bonding jumper is at the first means of disconnect. Any sub-panels off of the main DO NOT get one. Also, any current on equipment ground is objectionable current, not a ground fault. A ground fault will trip the breaker.
Edited 1/20/2009 12:25 pm ET by arcflash
"That main bonding jumper is at the first means of disconnect. Any sub-panels off of the main DO NOT get one."That is not what the code says through the the 2005 NEC..
William the Geezer, the sequel to Billy the Kid - Shoe
We are in 2008 NEC. Neutrals are bonded twice: at the transformer just prior to the point of service, and at the first means of disconnect. Bonding the neutrals to the grounds more than that creates an unstable system, basically doubles the chance for an unbalanced load to ground. The NEC is very clear about this. If you have a seperately derived system servicing an outbuilding, than yes, it will need the main bonding jumper.
"Bonding the neutrals to the grounds more than that creates an unstable system,"It has nothing to do with stability."basically doubles the chance for an unbalanced load to ground."What?The reason for only bonding at the one point in a building is that you want to form a reference point so that all conductive surfaces that you might come into contact with are at the same potential.And any conductor that you normally have current flowing through will have a voltage drop.So the only way guarantee that it all points are the same is to have a set of conductors that normally don't carry current. Thus the EGC's.If the EGC is bonded to the neutral, which normally carries current, at other places you will have voltage differences between different EGC's.However, there is no need to have the same potential on the EGC's in your house and your neighbors house because you would not be touching the faucet in one and the refrigerator in the other.If there is no common metallic paths between your house and your outbuilding then exactly the situation as between your house and the neighbors. And through the 2005 cycle the NEC allowed this to be feed with a 3 wire service and bonded in the outbuilding. In fact it still does. If the outbuilding is feed through a separate meter then is still bonded at the outbuilding..
William the Geezer, the sequel to Billy the Kid - Shoe
Your right about the potential differences, I digress. In my defense, however, I would like to say that not having a reference point could be considered instability. But you also answered the question about bonding jumpers in your last post. "If the outbuilding is fed through a different meter"........it becomes a seperate service requiring it's own disconnect, grounding electrode, and jumper. And for the record, you will have voltage differences on the EGC only during a fault on a system with two main jumpers, a potentially hazardous situation where not enough fault current is created on the ground to trip the OCPD, increasing the chance for an electrocution.I just read Scott's post and realized that we might be talking about a building with livestock. There is an entire section in the Code concerning this. And though I have never wired one, I do know that there are special circumstances regarding the grounding system. A barn with cattle might not be the same as an industrial dairy farm in the eyes of the Code.
Edited 1/20/2009 9:27 pm ET by arcflash
But none of that explains why a isolated neutral in needed in an outbuilding without anyother metallic paths, but only starting in 2008..
William the Geezer, the sequel to Billy the Kid - Shoe
"Right you are, the 2008 NEC says any feeder to a panel in a separate structure must be 4-wire (2 hots, neutral, equipment ground). "Cliff did you read any of the comments in the committees about this change?Other than the possibility that in their might be a metallic path sometime in the future I wonder what the logic was to require this change..
William the Geezer, the sequel to Billy the Kid - Shoe
"If this is impossible, I'd set up a fault monitoring program for the first subpanel--at least monthly, turn on all the lights and appliances, and heaters, in the barn, and measure the current in the grounding electrode conductor (wire from the ground or ground/neutral bar to the grounding electrode), using a clamp-on microammeter. If there's any current (more than a few mA), look for a fault."I am still confused about this.Is this only because of the livestock? Or is it because of the 3 wire feed to the first sub-panel.And if it is the 3 wire feed why wouldn't this be as critical for any place that you have a 3 wire feed. IE, any service entrance.And which ground electrode conductor are you measuring, the one in the barn or the one at the first sub-panel?I can see monitoring the ground equipment conductor between the sub-panels. But you can have a fair amount of current and if the EGC is working almost zero in the ground electrode conductor..
William the Geezer, the sequel to Billy the Kid - Shoe
I was once told by a seasoned old elec inspector that grounding rods were needed in cattle barns because milking cows were somehow extremely sensitive to ungrounded charges and would refuse to milk, hence the exception for livestock outbuildings.Otherwise, all outbuildings here must get their EGC from the main service panel.Scott.
Perhaps some of the confusion will go away if we return to basics.
The ground wire ... which goes back to the main panel, and ultimately, through the PoCo neutral back to the transformer .... THIS is what lets breakers trip, and fuses blow, if something goes wrong.
The rod you bang in the ground, and the wire to it, are there for lightning. That's why every structure gets a ground rod.
Now ... whatever we do, we make sure that the ground connects to that PoCo neutral at only one point, and that is as close to the meter as we can get it. If we did otherwise, any neutral current would be carried ... in part ... by every grounded part of the system. These things - like equipment cases and conduit - are NOT intended to carry current all the time.
Well, guys, as the poor forgotten OP, may I ask one more point of clarification? I get that the EGC is to be isolated from the neutral until it is as close to the meter as possible. But remember that my problem is that I am wiring a NEW 4-wire 240 circuit to the barn out of an existing box in outbuilding one. That existing box is fed by a legacy 3-wire 240 circuit from the main service panel.SO, to get down to brass tacks, or to copper-clad electrodes as the case may be -- do I bond the neutral and the ECG wire at the panel on outbuilding one, or do I just leave the ECG isolated and in contact only with grounding electrodes at the two buildings?Eventually, when we pull the new ECG from the main service panel in the house, I get that the I would have to un-bond the neutral and the ECG in outbuilding one, and run in isolation all the way back to the main panel. But for now to bond or to leave un-bonded -- that is the question.Joe
"do I just leave the ECG isolated and in contact only with grounding electrodes at the two buildings?"That is the most dangerous option.The ground electrodes often have very high resistance. They are their to supply a path for lightning and other surges."do I bond the neutral and the ECG wire at the panel on outbuilding one, or do I just leave the ECG isolated and in contact only with grounding electrodes at the two buildings?"Neither, not exactlyThe purpose of the EGC is to to provide a solid path for any fault current to flow and thus it need to return back to the neutral.At the out building the ground electrode is connected to the ground bus which is also bonded to the metal panel case. And the EGC connects to the ground bus.The neutral to the barn is connected to the neutral bus. Also the neutral feed from the house connects to the neutral bus.Then the neutral bus is bonded to the ground bus. That bonding might be done by a jumper from the neutral bus to the ground bus. Or a screw through the neutral bus into the case.So when you get the EGC run back to the house that will connect to the ground bus and the bonding screw/strap on the neutral bus is removed.That is the concept of how it is done.However, all panels don't have 2 separate buses. Some only have one and when you remove the bonding screw you will have to install separate ground bus and move things around. .
William the Geezer, the sequel to Billy the Kid - Shoe
The only advice that I can give you is to upgrade the outbuilding wire to a 4-wire system, that way your system is properly grounded and you wont have a "bogus" neutral out to the barn.
OK, well maybe what I should be getting is that I should just pull the 4th wire and leave it until the whole 4-wire system can be completed.I think I know how it should be when there are 4 wires from the main service panel right through to the sub panels and the sub-sub panel. The ECG will be isolated from the neutral all the way through and be bonded at the main service entrance. By means of the ground buses, it will also be in contact with the grounding electrodes in each building.SO, the ECG will connect to the ground bus in the barn and the ground bus in the outbuilding, and ultimately to the ground bus in the service panel which is bonded to the neutral bus only at that point. At the same time, the grounding electrodes (three rod arrays with cadweld connections) in the barn and the outbuilding will also connect to the ground buses in each building.Right now, there is no ECG from the outbuilding back to the main service panel, and there won't be until much later this year when I upgrade the panel and pull the 4th wire. There are only 3 wires -- the old-style 240 set up. That being so, I can't run the isolated ECG back to the main service panel.In effect, if the ECG is connected only to the ground buses in the barn and outbuilding, all it would really be doing is linking the grounding systems in each building and the grounding electrodes in each building. But there would be no return path from the ground system to the main panel.The neutral, on the other hand, would have the same clear path back that it does now in only one outbuilding without the barn being hooked up.Today, the way the system was set up (not by me, by the original electrician), the neutral and ground in the outbuilding are run to the same bus, hence bonded.So, am I better off:1) In effect to use the 4th wire to tie the ground system of the barn to the neutral bus in the outbuilding as a temporary measure, while leaving the grounding system in the outbuilding ALSO connected to the neutral bus; 2) To just leave the 4th wire unconnected and unused until the whole system is complete and for now have a three-wire system throughout with the neutral and ground bonded in each building;3) Leave the 4th wire unconnected and unused for now, but connect the grounding system in each building to the grounding electrodes and NOT to the neutral, leaving the neutral isolated all the way back to the main?Joe
"I think I know how it should be when there are 4 wires from the main service panel right through to the sub panels and the sub-sub panel. The ECG will be isolated from the neutral all the way through and be bonded at the main service entrance. By means of the ground buses, it will also be in contact with the grounding electrodes in each building.SO, the ECG will connect to the ground bus in the barn and the ground bus in the outbuilding, and ultimately to the ground bus in the service panel which is bonded to the neutral bus only at that point. At the same time, the grounding electrodes (three rod arrays with cadweld connections) in the barn and the outbuilding will also connect to the ground buses in each building."Yes."In effect, if the ECG is connected only to the ground buses in the barn and outbuilding, all it would really be doing is linking the grounding systems in each building and the grounding electrodes in each building. But there would be no return path from the ground system to the main panel."NO!"The neutral, on the other hand, would have the same clear path back that it does now in only one outbuilding without the barn being hooked up."NO!"Today, the way the system was set up (not by me, by the original electrician), the neutral and ground in the outbuilding are run to the same bus, hence bonded."And that was correct when done and is still correct because it is grandfathered in."1) In effect to use the 4th wire to tie the ground system of the barn to the neutral bus in the outbuilding as a temporary measure, while leaving the grounding system in the outbuilding ALSO connected to the neutral bus;"The problem with that statement is that there are two different "grounding systems". Then ground electrode conductors and equipment grounding conductor.Usually it is clear, by the context, which is meant by "the ground". But not in this case.Please go back to my past post where said exactly how the outbuilding panel should be wired.Then referencing what I said ask questions about anything that you don't understand.Edithttp://www.egr.msu.edu/age/aenewsletter/1_jan_feb_03/tinsey_1_30.htm#8Look at fig 4. The outbuilding would be wired like the panel on the left and the barn the panel on the right..
William the Geezer, the sequel to Billy the Kid - Shoe
Edited 1/22/2009 12:06 am by BillHartmann
You know, Bill, I genuinely appreciate the advice, but if I did understand it, why would I ask the question?Joe
Look at the edit I just added.But you are asking the same question.Instead work with what has been posted and say For example "You said '.....', but I am not sure if you are talking about the barn or the out building or what.".
William the Geezer, the sequel to Billy the Kid - Shoe
>>>The rod you bang in the ground, and the wire to it, are there for lightning.Not so. I'm talking about a grounding rod or plate that is for the equipment ground for a sub panel in an outbuilding. In the case of a cattle barn, you are allowed to bond the neutral to the ground bus and connect the ground bus to a rod. This would normally be a code violation, but livestock barns are given an exception.In all other cases sub panels must not have the neutral bonded and must only get their ground from the main service panel.Here's a reference:http://www.egr.msu.edu/age/aenewsletter/1_jan_feb_03/tinsey_1_30.htm#6Scott.
Edited 1/21/2009 11:43 pm by Scott
I don't know if that is still legal or not, but it is a dumb idea. A friend of mine killed almost all of his dairy herd when some truck with a whip antenna hit the overhead power lines going to the barn and directly shorted the hots & neutral.
The cattle were killed because they were chained to stanchions which were bonded to the neutral in the barn subpanel.
If the neutral had been floating at the subpanel, this wouldn't have happened.
>>>I don't know if that is still legal or not, but it is a dumb idea.According to many agricultural journals (do the search) it's not a dumb idea because cattle will not produce milk if they are subject to "stray voltage". Of course it's very sad about your friends herd, but I don't see how bonding the ground to neutral would kill cattle; in fact as long as there was a proper ground rod at the barn it should help. I suspect that someone might have been trying other stuff in an effort to minimize stray voltage.Scott.
Scott, I agree that stray voltage is a cause of problems with dairy herds and I don't think it is completely understood.
In this case, the neutral was connected directly to the cattle because the neutral was bonded to the metal works in the barn. When the antenna (or any other short) causes the neutral & hots to connect, this makes the neutral a hot wire and the cattle are well grounded standing on a concrete slab. This is what killed his herd.
If the neutral had not been bonded to the metal in the barn ( as in the 4- wire system) this probably would not have happened.
In the 4 wire system, you still would have the metal work grounded, but it would not be connected directly to the neutral at that location.
I don't know why you referenece the section that you did, but ignored this.http://www.egr.msu.edu/age/aenewsletter/1_jan_feb_03/tinsey_1_30.htm#8"Metal equipment likely to become energized that livestock touch is required to be connected to the grounding point of the service panel to a building. When a 4-wire system supplies a building, neutral current cannot flow to the grounding terminal in the service panel, and therefore, cannot get to the equipment livestock can touch. Even if there is too much current and resistance on the neutral supplying the building, livestock are not exposed to this potential source of NEV. Other sources, however, may still cause neutral-to-earth voltage that can reach livestock. The 4-wire electrical supply system does not prevent all sources of neutral-to-earth voltage.When a farm building is supplied power with a 3-wire system, neutral-to-earth voltage will not cause a problem for livestock in most cases where the conductors supplying buildings are properly sized, installed, and maintained, and the 120 volt loads are balanced. In some cases, 120 volt loads may operate randomly making it impractical to balance the loads. In cases where the distance from the distribution point to a building is long, and it is impractical to keep the loads balanced, it is recommended that a 4-wire supply be provided to those buildings where livestock may be exposed to grounded equipment such as heated waterers.".
William the Geezer, the sequel to Billy the Kid - Shoe
Ignored? I don't know what I ignored.
It give the reason that 4-wire is better.And while it does accept 3 wire it is an older document and the NEC does not allow 3 wire sub-panels any more..
William the Geezer, the sequel to Billy the Kid - Shoe
I agree that a 4 wire system is better, and I didn't ignore it. It's important to note that they still recommend a grounding electrode at the barn though, which is different from a regular outbuilding.Scott.
"recommend a grounding electrode at the barn though, which is different from a regular outbuilding."That is where you are wrong.EVERY structure is suppose to have it's own grounding electrode system..
William the Geezer, the sequel to Billy the Kid - Shoe
I don't get. For example, my house is technically an outbuilding because the main service for the property terminates in another building. So the panel in the house is actually a sub panel of the main one in the other building.So I unsnapped the bonding lug so the house has an isolated ground conductor coming from the other building.Are you saying that it's normal for a building like this to also have a separate ground electrode (as in the fig. 4 diagram) attached at this end of the ground conductor?Scott.
"Are you saying that it's normal for a building like this to also have a separate ground electrode (as in the fig. 4 diagram) attached at this end of the ground conductor?"Not only normal, but required.From the 2005 NEC."250.32 Buildings or Structures Supplied by Feeder(s) or Branch Circuit(s)(A) Grounding Electrode Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with 250.50. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed."This is from the Handbook Portion. It is not code but extra clarification and explanation."Where a building or structure is supplied by a feeder, 250.32(A) requires that a
grounding electrode system be established at each building or structure supplied,
unless one already exists. The equipment grounding bus must be bonded to the
grounding electrode system, and the disconnecting means enclosure, building steel, and
interior metal water piping are also required to be bonded to the grounding electrode
system. All exposed non–current-carrying metal parts of electrical equipment are
required to be grounded through equipment grounding conductor connections to the
equipment grounding bus at the building disconnecting means. The connection of the
grounded (neutral) conductor to the grounding electrode system, as shown in Exhibit
250.16, is permitted only where it can be ensured that such a connection does not
establish a parallel circuit path for normal neutral current on equipment grounding
conductors, metal shields of cables not intended to be used as a current-carrying
conductor, metal piping systems, or other metal structures that are continuous between
buildings."Code;"Exception: A grounding electrode shall not be required where only a single branch circuit supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the conductive non–current-carrying parts of equipment. For the purpose of this section, a multiwire branch circuit shall be considered as a single branch circuit.""(B) Grounded Systems
For a grounded system at the separate building or structure, the connection to the grounding electrode and grounding or bonding of equipment, structures, or frames required to be grounded or bonded shall comply with either 250.32(B)(1) or (B)(2).(1) Equipment Grounding Conductor
An equipment grounding conductor as described in 250.118 shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s)."This is the 3 wire option which is no longer allowed by the 2008 NEC"(2) Grounded Conductor
Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in each building or structure involved, and (3) ground-fault protection of equipment has not been installed on the supply side of the feeder(s), the grounded conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of either of the following:
(1) That required by 220.61
(2) That required by 250.122"Handbook"Similar to the provisions of 250.30(A)(3), the requirement in 250.32(B)(2) eliminates
the creation of parallel paths for normal neutral current on grounding conductors, metal
raceways, metal piping, and other metal structures. In the 1999 and previous editions
of the Code, the grounding electrode conductor and equipment grounding conductors
were permitted to be connected to the grounded conductor at a separate building or
structure. This multiple-location grounding arrangement could provide parallel paths
for neutral current along the electrical system and along other continuous metallic
piping and mechanical systems as well. Connection of the grounded conductor to a
grounding electrode system at a separate building or structure is permitted only if these
parallel paths are not created and if there is no common ground-fault protection of
equipment provided at the service where the feeder or branch circuit originates.
Where the grounded conductor is used as part of the ground-fault current return circuit,
it is required to be sized no less than that required by 250.122 for equipment grounding
conductors, but it also has to be sized to carry the maximum unbalanced load, as
specified in 220.61.
Like the grounded service conductor, a branch-circuit or feeder grounded conductor
used in the application permitted by 250.32(B)(2) is a circuit conductor for normal
neutral current and is also the circuit conductor used to create an effective ground-fault
current return path. Therefore, it is necessary to size the grounded conductor in this
application based on which of those two functions requires the larger conductor. Of
course there is no prohibition on installing a full-size grounded (neutral) conductor,
thus ensuring compliance with both 250.122 and 220.61."(C) is for ungrounded system which is completely different than what we are talking about and is not commonly used..
William the Geezer, the sequel to Billy the Kid - Shoe
Must be different here (Canada), which surprises me because the Canadian code is usually right in step with the NEC.My house is only four years old, and though I had everything inspected (and believe me, our inspector does EVERYTHING he can to make things difficult for homeowners, especially homeowners that choose to wire their whole house), there was no mention of an independent ground rod at the sub panel end. Is this a fairly new requirement?Scott.
I don't believe that it is new. It was that way back in the 99 NEC, but I don't have any idea of how old it might be.But there are lots of small differences in the Canadian and US codes..
William the Geezer, the sequel to Billy the Kid - Shoe
The additional ground rod is called for at a 'detached structure' that has more than one circuit to it. An additional panel within the same structure does not require an additional ground rod.
Right, that's a big difference from here. In fact, I remember back in the 80s when I added a small subpanel to my garage, I naturally thought a grounding plate would be a good idea but the inspector forbade it. I vaguely remember him muttering something about "ground looping".As for this house that we built lately, there was nothing mentioned by the inspector, nor when I carefully read the residential portion of the code book (snooze....) did I see anything about additional ground rods. Strange huh?Scott.
Edited 1/22/2009 1:27 pm by Scott
"I vaguely remember him muttering something about "ground looping"."A lot more people use that term than have the slightest idea of what it is or when it might cause problems..
William the Geezer, the sequel to Billy the Kid - Shoe
"Ground loop" is largely snake oil when you are talking about power distribution.
The real issue is "objectionable currents on grounding conductors". That is the whole point in the 4 wire feeder. You will not see voltage drop imposed on the neutral showing up on your EGC when you run 4 wires. When you have a 4 wire feeder the ground rod at the second building only tends to be sure you are mitigating ground shift and being a little more sure that the case of your power tool is at the same potential as the concrete floor of the shed/garage.
Personally I prefer a Ufer for that exact reason.
Bill:The diagrams are helpful. My continuing worry, though, is that the outbuilding panel is not the first disconnect after the meter, it is the second one. Is that cause for concern?Joe
"The diagrams are helpful. My continuing worry, though, is that the outbuilding panel is not the first disconnect after the meter, it is the second one. Is that cause for concern?"No.It was correct when wired. And it does not affect the wiring to the barn or the operation of the barn in anyway..
William the Geezer, the sequel to Billy the Kid - Shoe
Right, but it was originally wired with no grounding electrode. I plan to add one.This is not a code issue, simply a safety one. There is no code out here.Joe
To be honest I don't see why they even drop the 3 wire option.How 4 wire it is somewhat better in the barn.And it required and makes sense where you have other metallic paths.But I don't see any logical reason that they even got rid of it..
William the Geezer, the sequel to Billy the Kid - Shoe
Best I can tell, Bill, is that the 4th provides an additional path back -- belt and suspenders.However, I am aware of but do not technically understand lots of barn problems involving neutrals that were re-grounded at the barn, and wanted to avoid those. Seems I will on the present plan.J
BTW, if the footings are not already in you should use a UFER ground electrode.That is 20 ft of bare copper wire or rebar in the footing.The rebar can't be coated and you can splice multiple pieces with tie wire to get the lenght.Easiest method is to bend of the end of a piece of rebar so that it will be sticking out of the slab when finished. And then make the connection there.Otherwise you need an approved clamp and clamp the ground electrode wire to the rebar before the pour and protect the wire during construction..
William the Geezer, the sequel to Billy the Kid - Shoe
Thanks, BIll. I am aware of Ufer, but this barn has been around a long time. We are just tired of having to run a long #12 cord when we need juice for something, so I'm going to run underground service. if I go to that large PIA, I want to do it once and do it right.J
I asked my foreman the other day why some hight voltage appliances required a neutral, and some did not. I wanted to know when I need to pull a 4-wire vs. a 3-wire (a rule of thumb approach, without checking submittals). His answer made alot of sense. If the appliance has alot of electronic components, chances are that you will need that neutral. More and more products--appliances, tools, whatever, have more and more advanced electronic components. You cannot add a jumper to the sub-panel. A four wire system behind a three wire system is really a three wire system. Upgrade.
Well, right. I do plan to upgrade, but can't do it now. So, I guess I'll pull the 4th wire and just leave it unconnected.What jumper were you referring to?Joe
"I asked my foreman the other day why some hight voltage appliances required a neutral, and some did not. I wanted to know when I need to pull a 4-wire vs. a 3-wire (a rule of thumb approach, without checking submittals)."You are confusing things.First I think that you are talking about residential appliances.240 volts is still "low voltage". There are some code changes at 300 and lots of them at 600. That would be high voltage.Even 240, as used in residences is still only 120 to ground.As to appliances. Dryers and ranges require both 120 and 240. Thus they require a NEUTRAL. This is nothing new and has nothing to do with "electronics".For dryers it was for the motor and timer.And on older ranges they burners had 2 elements and multiple position switches and connected one or both elements and in series or parallel across 120 or 240.Also for the oven light. And old stove often had a 120 convenience receptacles on them.Under the code before 96 you where allowed to run those WITHOUT AN EGC.They would have 2 hots, and NEUTRAL. And you bonded the case of the appliance to the neutral.And those are still specifically called out in the code as allowed existing unless it is off a sub-panel (often apartments and mobile homes). But I understand that some local codes prohibited this long before.New installation require a separate 4 wire installations. 2 hots, neutral, and EGC.Now some specialty versions and particularly cooktops might not require 120. But I would always run 4 wire for those because you never know what they might be replaced with in the future.In general no other common 240v residential equipment requires a 120 thus no neutral. 2 Hots and an EGC.Thus includes AC, electric furnaces, saunas, well pumps.I think that some hot tubs can run on either 20 amp 120V with limited capacity or 50 amp 240. I am not sure, but I believe that some of them require 120 with the 240 when working in that mode. So there 2 different types of 3 wire 240V circuits. .
William the Geezer, the sequel to Billy the Kid - Shoe
If you want to be pedantic 600v up to around 13,000 is medium voltage and high voltage is over that but "1&2 family" guys who think anything on the line side of the meter is spooky stuff they don't care about, say low voltage is anything under 30 (the 725 definition).
Barns, and other agricultural clusters of buildings, are allowed some variations in how the power is distributed throughout the site .... but grounding doesn't change. What variations there may have been in interpreting the NEC were cleared up in the 2008 edition.
That is ... your "main" is at the first disconnecting means after the meter. This is the only place where you bond the neutral to the ground. Everywhere else ... whether another panel in the same building, or a separate building fed from that source .... has the ground and neutral busses kept separate. You have a properly sized ground wire connecting all these busses, all the way back to that main disconnect.
Even in a dairy shed, with all the concern over 'equipotential planes,' the grid is part of the groundin network - the same network to which the ground rod is connected.
Saying that the ground rod is 'just for lightning' is, I admit, an oversimplification .... but what has to be made clear is that the dirt under our feet is NOT a conductor, does nothing to help current flow back to the PoCo transformer, and will do nothing to keep you from getting shocked. It will not let breakers trip or fuses blow. Ultimately, the only way those safety devices can work is for there to be a clear, low resistance path back to that transformer. This can only be accomplished by there being, at some point, a connection to the PoCo neutral.
Let's say you DO connect the ground to that neutral at your barn. Well, you have just created a possible path - through the dirt - for some current to flow from building to building. Since dirt is a poor conductor, you have just created the 'voltage gradient' that the 'equipotential plane' attempts to eliminate.
Keep neutral and ground apart. period. Fail to understand this, and you WILL kill someone, someday. This very issue is at the center of plenty of 'stray voltage' furballs as we speak.
>>>Keep neutral and ground apart.I completely agree. The agricultural exception is more of a curiosity to me, and I was surprised to here about it from an inspector. He was an old guy, and the year was 1999, so he may not have been aware of some new developments.Scott.
You're half right.
Outbuildings with more than one circuit get ground rods. Period. These ground rods have a wire that is connected to the grounding buss in that outbuilding's panel.
In the outbuildings' panel, there are separate ground and neutral busses. You do NOT use that green screw.
Rather, you run four wires to the main panel in the first building, and terminate them in the appropriate places. This main panel - or disconnect, if you're using a disconnect separate from the first panel - is the only place where the neutral buss is bonded to the case, and where ground wires share a buss with neutral wires.
OK, I think I follow (oh for a white board). Neutral in barn is not bonded to the case. Neutral and ground are kept separate back to the panel in outbuilding one, where they ARE bonded. Both outbuildings have grounding electrodes.When the 4th wire is run back to the main service panel in the house, do I at that time UNBOND the neutral and ground at outbuilding one, so that each runs back separately to that main service entrance? JoePS, as a matter of curiosity, what work does the neutral really do in a 220 installation if the opposing phases of the 2 hot legs cancel each other? Does it come into play when there is an imbalance in the legs?
Edited 1/20/2009 8:29 pm ET by Joe Sullivan