grounding and bonding

[papa smurf]

Before the 5 wire rule and when electricians ran 4 wire for a 3 phase system starting at the owner supplied stepdown transformer and if you had a mdp at the pad mount transformer grounded going to a grounded electrode, then 400 ft later another main breaker at a pedlestel 30ft. from bldg. then another main on the building that fed 2 sub-panels and all had 4wires 3hots and 1 neutral and they had the main at the bldg grounded to a grounded electrode. My question is at how many panels do you bond the neutral and ground together under the old code.

 

[wbalsam1]

Not on the load side of the service disconnecting means. Been that way for a lot of years. Connecting neutral and ground downstream from the service OCPD means that current divides along all the paths it's given and may not be enough during a fault to operate the OCPD's.

 

[papa smurf]

this system is a 4 wire system and can not run a 5th wire. the frame of the transformer is grounded but not bonded to the neutral. the frame ground is tied to the equip. ground at the mdp. the neutral and ground bar are not bonded at no point there creating a floating neutral in the system. So if you read the original question you will see that the neutral and ground are not bonded anywhere along its path. As you can see i have many mains and trying to find out if i should install a ground rod and bond the eqip. ground with the neutral at each point. Sorry if i wasn't clear and hope this helps.

 

[wbalsam1]

this system is a 4 wire system and can not run a 5th wire. the frame of the transformer is grounded but not bonded to the neutral. the frame ground is tied to the equip. ground at the mdp. the neutral and ground bar are not bonded at no point there creating a floating neutral in the system. So if you read the original question you will see that the neutral and ground are not bonded anywhere along its path. As you can see i have many mains and trying to find out if i should install a ground rod and bond the eqip. ground with the neutral at each point. Sorry if i wasn't clear and hope this helps.

I cannot see how a ground-fault could possibly clear. A phase-to-ground connection would not be able to get onto the neutral (grounded conductor - this conductor is not grounded in your scenario). A phase-to neutral could clear, but not a ground-fault.
Typically, the grounded conductor is bolted to the grounding electrode system at the service means. This way, a fault on the equipment grounding conductor of a feeder or branch circuit would have a connection to the grounded conductor at this location and be able to clear.
Typically, 3 phase systems require an equipment grounding conductor run with the circuit conductors downstream of the MDP and they also require the GES be connected to the grounded conductor at the service means.

 

[papa smurf]

I cannot see how a ground-fault could possibly clear. A phase-to-ground connection would not be able to get onto the neutral (grounded conductor - this conductor is not grounded in your scenario). A phase-to neutral could clear, but not a ground-fault.
Typically, the grounded conductor is bolted to the grounding electrode system at the service means. This way, a fault on the equipment grounding conductor of a feeder or branch circuit would have a connection to the grounded conductor at this location and be able to clear.
Typically, 3 phase systems require an equipment grounding conductor run with the circuit conductors downstream of the MDP and they also require the GES be connected to the grounded conductor at the service means.

I don't believe your reading this carefully and understanding what i'm saying. Nice try.

 

[don_resqcapt19]

Under the 2005 code you could probably bond at the transformer, pedestal, and the building main and be code compliant. You need an EGC from the building main to the subpanels. Under the 2008 code you could bond at the transformer or the first means of disconnect. You would need the 5th wire to all of the other locations.

 

[hornetd]

Why the question

Why the question

Before the 5 wire rule and when electricians ran 4 wire for a 3 phase system starting at the owner supplied stepdown transformer and if you had a mdp at the pad mount transformer grounded going to a grounded electrode, then 400 ft later another main breaker at a pedlestel 30ft. from bldg. then another main on the building that fed 2 sub-panels and all had 4wires 3hots and 1 neutral and they had the main at the bldg grounded to a grounded electrode. My question is at how many panels do you bond the neutral and ground together under the old code.

I need to know if the question is a historical inquiry or a question about an existing installation that you need to deal with now in order to answer intelligently. I have worked on installations like the one you describe, I think, and they were a tough nut to crack. In the ones I have encountered the neutral was bonded to the enclosure and to the grounding electrode until you were inside the building. The feeder supplied panel's cabinets and the metal raceways and cables they supplied were also bonded to the neutral at each panel. There was neutral current flowing everywhere. In the one case were it was all in metal raceway I simply checked the continuity of the raceway containing the feeders and removed the bonding to the neutral at each feeder supplied panel.

In the other case I can recall it was a huge dairy farm with over two hundred head of milking cows not including calfs, bulls, and other incidental stock. The wiring methods were like a historical museum of every electrical wiring method ever used from knob & tube to brand new non metallic surface raceway. In that case I did a hell of a lot of rewiring in all of the structures that had anything to do with the stock. I got a pretty nice bonus when the milk production went up rather sharply. I was originally called in because one of the ranchers family had gotten a shock off of a switch box. All of the switch boxes had been bonded to the neutral by winding the stripped neutral conductor around one of the brass mounting screws. Since by the time they had hired me nearly everything in the wiring system of the barns and milk house was corroded the neutral current was taking any path it could find to return to the transformers. That included one of those metal cored plastic covered clothes lines that became popular in the sixties. The clothes line was carrying some of the neutral current back to the house from the metal roof of the milk house. The women of the family had stopped using that clothes line because "it felt funny." Once the wiring was cleaned up the family started telling me about all the strange stuff that was no longer happening. As far as i was concerned the whole clan was lucky to be alive. I think that was the only three phase dairy farm I ever worked on. Nobody still living there new why the service was three phase. Only the milk chiller and the hay bale lift had three phase motors. Since they already had three phase power to the buildings every motor I replaced was three phase when I was done with it. Including some shop tools, the homes furnace blower, and the barn cooling fans. Since I had felt the ranchers eyes on me the whole time I was there the bonus was a big surprise. Turned out I was under watch to prevent any chatting up of the rather pretty daughters that I had mistaken for wives of the several sons. I have never seen a set of sisters look so different in a family were it wasn't easy to tell the sons apart.

 

[tryinghard]

Before the 5 wire rule and when electricians ran 4 wire for a 3 phase system starting at the owner supplied stepdown transformer and if you had a mdp at the pad mount transformer grounded going to a grounded electrode, then 400 ft later another main breaker at a pedlestel 30ft. from bldg. then another main on the building that fed 2 sub-panels and all had 4wires 3hots and 1 neutral and they had the main at the bldg grounded to a grounded electrode. My question is at how many panels do you bond the neutral and ground together under the old code.

Two questions we have to ask ourselves:

• 
  1 ? Is the neutral (returning) current traveling to its source exclusively on an intended conductor?
  2 ? Is there an intentional effective ground fault current path to source?

These two duties (so to speak) have always been separate unless it?s ahead of the service disconnect. The ground fault path used to be mostly mechanical (conduit) in the old day?s but neutral current has never been allowed on anything other than a conductor.

 

[buffnitup]

grounding electrode conductor

grounding electrode conductor

Ok guys. I have alot to learn. This may be in the wrong place but I will go ahead and ask. Ok. No metal water. No metal frame. Ok in the NEC it says the grounding electrode conductor shall be connected to the grounded conductor in the service disconnect enclosure. Got that. Then it also says it is permissible in the panelboard to be connected to the ground bar if the main bonding jumper is installed. Does it have to be both? Also would I have to run a bonding jumper back to the disconnect from the panelboard? I would think since it is a connected in the panelboard it would return back to the disconnect to the ground rod outside in a fault situation.

 

[ericsherman37]

Ok guys. I have alot to learn. This may be in the wrong place but I will go ahead and ask. Ok. No metal water. No metal frame. Ok in the NEC it says the grounding electrode conductor shall be connected to the grounded conductor in the service disconnect enclosure. Got that. Then it also says it is permissible in the panelboard to be connected to the ground bar if the main bonding jumper is installed. Does it have to be both? Also would I have to run a bonding jumper back to the disconnect from the panelboard? I would think since it is a connected in the panelboard it would return back to the disconnect to the ground rod outside in a fault situation.

Normally I believe the MBJ would be installed at the service disconnect, and the GEC would be also tie into the grounded conductor in that enclosure too. So from there on out, you'd have a separate grounded conductor and EGC, including at the downstream panelboard.

I don't know if there's an allowance for bonding the GEC and grounded conductor at the service disconnect and then creating your EGC at the panel. It seems like it wouldn't hurt anything as long as the panel wasn't too terribly far away. But I don't know and I'm too lazy to look it up I'd personally try to do all of the service grounding and bonding in one enclosure, if possible. Makes things simpler.

Our instructor always asks us "How many times do you bond the neutral?" The answer: "Once." Where? "At the service?" Where else? "Nowhere else, get the idea out of your heads."

 

[buffnitup]

Ok. I do understand somewhat on what you are saying. It is kind of confusing. What isn't about the code in some cases? Here is the setup I am planning. Pole outside will have the service mast then meter then disconnect. I will be putting one breaker for the manufactured home rated same as whatever the OCPD is inside the home. Then probably a 50A to a barn. Ok I know all about the voltage drop and ampacity sizing for the most part. Even after 2 years of school I am still learning different stuff. Now correct me if I am wrong.. If I were to run straight from meter to panelboard then the main breaker in the panel would be my disconnect means and be classified as the service equipment correct? So bonding the neutral and grounding bar in this enclosure would be the MBJ(which is usually connected by a bar already or optional) then connect the GEC to the ground bar and to the rod, plate, what have u? Right? So my deal is if I bond the neutral and GEC outside in the main disconnect and shoot it down the the rod do I need to run an EGC(from EGC bar) from panel back to disconnect, making sure the neutral and EGC bar are not bonded in the panel but only at the disconnect. Would that be right? I don't want to install 2 rods if it is not needed. I'm guessing in this case the panelboard would be considered load side and I think it says that no neutral can be bonded to non-current carrying parts on the load side. Maybe I am making more confusing than it should be lol