Neutral and Ground Separation

[Kidd6488]

Thanks rewired, and everyone else, but rewired, you gave some nice details, and told me what I half-expected to hear, about bonding at the disconnect, because technically, isn't that where the 'service' ends? I thought the term 'service' applies to everything up to the first disconnect (which would be outside in my case). Also, this would explain why they ran 4-wire in from the disconnect in the first place.

So if I bond the neutral to ground outside in the disconnect box, i should leave the bonding screw in, in the main breaker box (its only bonding the case to gnd, not neutral to gnd), right?

Thanks a lot,

~Jonathon Reinhart

[Rewired]

Hey!

Glad i could help you out with the details!
First: About the bonding screw issue in your MAIN panel.
What should be done there is the "jumper bar" you Removed should be re-installed.. those bars on each side of the panel are neutral buss bars. You should add a grounding buss in your panel for ALL the grounding wires alone. It will be safer this way because the way it sounds you have it now, if the bonding screw were to get removed somehow, you would lose the bond between your panel enclosure and the now "ground" bar.. The potential for the enclosure to become live if there was a fault inside the panel is very likely the way you have it bonded together now, relying on the "bond screw" to bond the the enclosure to ground.
Second: Bonding neutral to ground at the main disconnect will be correct now. it will be "grounding" the service as it enters your house... (keeping neutral at "zero volts").

Now, Johnathon, look at how I described it there.. Now, picture what would happen if that "bond" between neutral and ground in your main disconnect was to be removed or somehow "disappear". Your "service" would become ungrounded, BUT all the grounds and metal enclosures would STILL be bonded together via the grounding / bonding wires and in turn bonded to the ground rod would they not? That means the every piece of "grounded" metal would still essentially remain at "zero volts" there would be no risk of something becoming live should something fault out, the WORST that will happen is you could show a wierd "voltage to ground" from your service wiring.. thats about it..

I hope I didn't confuse ya, let me know if I did I will sort it out for you!
A.D

[Kidd6488]

Ok, about the neutral/ground bars... This box is already wired, and very wired it is. It would be nearly impossible to change the grounds to a different bar, as they would be too short. The box may be set up correctly as the manufacturer intended, but the instructions aren't clear enough. Personally, I wouldn't worry about the bond screw coming loose, and we can even put some loctite on it to be safer. And say it does come out, and there is a line-to-case fault in the box, there is all kinds of contact from the bare grounds to the case, just by the freak chance that both conditions become true.

As for your second paragraph, I understand what you are saying. But I was reading elsewhere, and correct me if I am wrong, but aren't the electrons coming from the transformer seeking to get back to the transformer, not back to the earth? They might go to earth, but only because the center-tap of the transformer is grounded out at the pole (to its own ground rod).

So, if in some metal outlet box, for example, say a hot wire comes loose and touches the metal box. Now, lets say that the main system bonding jumper (I think it is called) is not there, and neutral and ground are separate. All metal boxes are now at 120V. For the electrons to return to neutral, which they are seeking to do, they must go through the grounding conductors, into the grounding electrode, through the earth 150' to the other ground rod out at the transformer, up the grounding wire, and up to the neutral conductor (center tap). By now, we probably have many ohms in the path, only allowing several amps to flow, and the circuit breaker sees only say 5A flowing through it, which it sees as fine. So the metal boxes remain at 120V touch voltage, waiting for someone to touch it and fry.

Now, I argued this to my dad, and he says that no, the electric is going to go to the ground rod, because everything wants to... But I said, If you take a 9V battery, and put a voltmeter from one terminal to a ground rod what will you get?

So am I correct?

Thanks again for everything...

~Jonathon Reinhart

[HayZee518]

Let me explain this to you from experience. I went on a service call to a house where the guy replaced a Sears broiler/oven. He made the splices in the box exactly the way he took them out. But when he turned on the breaker the oven did not function. I measured 220 on both hots and 110 on each leg to the bare ground wire. I went tracing out the wire in the basement and found another splice box above a dropped ceiling. I opened the box and pulled the wires out. Then I grabbed the bare wire and the dropped ceiling grid and BOY DID I GET A RAP!!! I checked with the meter and had 110 volts to the grid system. I should NOT read anything to this. It should be zero. Went to the main panel and took off the cover. The bare ground was just floating in the box - No connection to the neutral block. It may had touched something at one point or another so the original oven worked. I put the wire in the neutral block and tightened it and voila! The oven worked perfectly.

[Kidd6488]

I don't understand what was going on... It was 3-wire to the oven, I presume, and the oven needed the neutral for the 110 components, but how did you measure 110 to the ground? And I'm guessing you were being the link between the oven's nuetral and the ground, and so you had a hot nuetral, and thats why it hurt so bad... But how did you get 110 when you measured?

And does that prove me or my dad correct, or neither?

~Jonathon Reinhart

[HayZee518]

The elements are connected across both 120 volt legs = 240. The light inside and the clock timer are 120 volt. They connect across one leg to the neutral or in this case the bare ground. So what you're reading is the return to ground through the device. By me touching the bare wire and the grid I was completing the path to EARTH ground before the path it would normally take to the main panel. I was a better path than that floating bare ground in the panel.

[Kidd6488]

Oh I see, the impedance of the 120V components were giving you 120V. I was thinking this was a range outlet, and the range was unplugged. I understand now.

~Jonathon Reinhart

[Kidd6488]

If this helps anything, here are pictures of our MAIN disconnect box, and breaker box.



Here's the neutral lug, with a third lug, and bonding screw hole. Would this be the way to bond the system neutral to ground? It's a 10-32 screw which the installers lost, so we would have to get a new one. Or, would I just run a large (#6?) wire from that third little lug and clamp on to (with a split-bolt lug) one of the other ground wires in the disconnect?



And here's our panel box, with ground bar on left, and neutral bar on right.



~Jonathon Reinhart

[Rewired]

You are right about there being or could be several ohms in the grounding path back to the transformer. You are correct there as well, a fault current is going to try to return to the transformer, NOT just "into the earth", it will use the path through the earth if its easiest. Oh ya, I see your pictures now. To make the bond in the disconnect I would use a BRASS screw in the place where the original one was located.. Usually the ones I have seen are brass..

One experience of several I had with wierd / bad grounds was a few years ago, I was doing a panel change at the neighbours across the street, and had the 2 hot wires and bare neutral (yes, it was allowed here) hanging out of the LB fitting at the side of the house, and was about to disconnect the old ground and remove the old panel from the wall (keep in mind the panel was still in contact with "ground" through the metal conduit, where it is also bonded in the meter socket!
Anyways, I unhooked the old ground to the water pipe and got a nice arc!
I connected it back and did a load check and found out there was 7 amps cruising OUT of the water pipe and up the service , back to the transformer! Keep in mind there is NO POWER present in the building as the meter was unplugged from its socket!
The only reason I can see this happening is someone in the court must have a bad neutral in their service, and any unbalanced neutral current is going through their bonding jumper, through the grounding conductor, to the metal water pipe, under the street, up the water pipe of the house I was in, and back up the service to the transformer! (the house I was in was closest to the poletop transformer.. Sounds a bit wierd eh? I have seen this sort of thing several times!

A.D

[HayZee518]

Could be a fault on a device and the unbalanced load is just taking the easiest path back to ground. As a rule if a fuse is put in between the grounding conductor and the ground rod - if it blows - there's a problem because there should be NO potential on the grounding wire.