sprdave

Im an apprentice in Ontario (Canada), I'll try not to make a fool of myself . Unclear now on this bonding neutral.

I've always thought you bond the neutral to ground at one place at the service, then keep the bond and neutral separate after that. And when running to another building you could run a bond (4-wire feed) keeping neutral and bond separate, or run a 3-wire feed and bury a ground plate at the subpanel for ground/bond, again keeping the neutral separate.

but rule 10-208(a) says
the grounded circuit conductor at each of the buildings or structures shall be connected to a grounding electrode and bonded to the non-current-carrying metal parts of the electrical equipment.

which seems to be saying to bond the neutral at each building, but to me would promote ground current? Explain

What do you do when you run to a subpanel in another building with a ground plate?

wcord

IF I don't carry my ground along with the neutral, then I bond my neutral with rods or a plate.
10 208 is implying that each building is a separate service.
In regards to a ground current, bonding to neutral is in reality, just in case the neutral looses connection, so there should be no current.
When there is a current on the ground, that's what is referred to as "tingle voltage"

erics37

Can't speak for Canada but under NEC a separate building has to have isolated neutral and EGC and also has to have a grounding electrode system bonded to the EGC.

* Make that "grounded circuit conductor" instead of neutral.

sprdave

10-208 "where two or more buildings or structures are supplied from a single service" Im confused what you(this) means?

The last subpanel (separate building) I looked at (done by different electrician) that had a 3-wire feed (no bond) and grounded at the panel, didn't have the neutral bonded that I could find...so is this wrong?

So by bonding the neutral again, current wouldn't possibly go to the ground, which is then a second path for the neutral current? (the same way a fault (short) current would flow through the bond to the ground, except during normal operation it flows through the neutral to the subpanel bond to ground)

Grounding the circuit (bonding neutral) from my understanding, is for if there is a short (to something grounded), it gives a route for fault current to flow (through the ground, back to where the ground is bonded to neutral), and trip the overcurrent device. If the neutral disconnects it would do nothing (unless it connects to ground)

wcord

upon further thought, i believe you are correct. The majority of my outbuildings were on farms , where the feeds were overhead from a central point (farm service), so therefore the service points were located at each building.
i have to admit, after doing this for so many years, it sometimes takes a fresh approach to actually think about whats in the code

I am trying to remember if there was something in the code about having a separate ground for a panel fed from elsewhere. In the back of my mind it had to do with setting up a current in the ground.
IF the building is fed from the main service, and the ground goes with the feeds than the neutral is left unbonded at the outbuilding. IF there was no ground taken with the feeds, than you must bond the neutral to the ground

maybe one of our more knowledgeable members has a better understanding of this code

xlink

At one time, we were allowed to take a feed from a panel without a ground and to ground the neutral at the second building. The feed to the second building would be with service entrance cable like USEB. Then, it wasn't allowed. Then it was allowed, or wasn't. I don't remember where we are now but you can't tell by looking at an old job whether it complied with the rules. It probably depends on where you are.

stuiec

Doesn't it depend on whether or not the outbuilding houses livestock? ie, needs a new electrode (due to step potential with cows etc) where livestock is concerned?

Dang, now I have to look it up.

backstay

That is a whole other story, equatorial ground coming into or out of a building for livestock. It must be connected to the GEC but is much more than a ring or two ground rods.

__________________
When "deleted" called the Seals, they killed Bin Laden. When the Seals called "deleted", he denied them.

stuiec

We have a choice:

10-208 Grounding connections for two or more buildings or structures supplied from a single service
Where two or more buildings or structures are supplied from a single service,

(a) the grounded circuit conductor at each of the buildings or structures shall be connected to a grounding electrode and bonded to the non-current-carrying metal parts of the electrical equipment; or

(b) except for buildings housing livestock, the non-current-carrying metal parts of the electrical equipment in or on the building or structure shall be permitted to be bonded to grouind by a bonding conductor run with the feeder or branch circuit conductors.

stuiec

I have no experience in this area. Anyone know where in the CEC I can read about this?

sprdave

I think Im just getting myself more confused the more I ask

Maybe Im looking at the flow of things wrong....

To illustrate, if the first building has a service disconnect/panel (I'll call it "A") with a grounding electrode that is bonded to the neutral. A 3-wire feed (no bond) runs to subpanel at a secondary building ("B") with a grounding electrode that is bonded to neutral as well. Would ANY neutral current from a load(s) on "B" flow to "B", cross the bonding jumper in "B", out the ground electrode, through the earth, to electrode "A", through the bond jumper on "A" to the neutral back to the power source?? (Or am I just thinking way to hard )

IF nothing would flow in that case, that means if something shorted, the current couldn't flow through "earth" back to the neutral bond. Instead it is dependent on the bonding system (bonding conductors, metal structure, piping, etc) to get back to the neutral bond (in "A" or "B")?

Which means the ground electrode does nothing in the event of a short, it just disipates any stray voltage difference to ground?? And the bonding system ensures a path back to the neutral.

Which also means if the main neutral disconnects, then the bonding system is "live"?

xlink

You are only allowed one neutral-to-ground connection at each building because multiple connection points cause the bond wire to carry current.

In the case of separate buildings, there is a benefit to grounding the neutral because it brings neutral to earth potential. However, if you ground the neutral at the second building and have a bond wire between buildings, it puts the neutral in parallel with the bond wire and significant current will flow on the bond wire.

When you remove the bond wire, the earth is in parallel with the neutral. Earth, with ground rods is a high resistance and, in parallel with the low resistance neutral, little current flows through the rods.

For what it's worth, in the case of a short, a ground rod might not trip a breaker. That's the reason we only need a #6 wire to a ground rod, even on a larger service.

I'll show you how to start a fight: The grounding system always carries current because it's in parallel with the neutral.

sprdave

I think Im starting to grasp it...the problem was the ground being a second neutral path, but the current must be little enough that it's considered negligible.

This means that if there is no bond with the feed and the subpanel neutral isn't bonded, it would be depending on earth for fault current...which is high resistence.

So how long have these rules been around as they are?? The subpanel I referred to without a bond feed and neutral not bonded was put in about 1995 by an electrical contractor at a relatives. Which means it's depending on earth for fault.......

AND they have a livestock barn, that has a subpanel supplied from another barn...originally put in 15-20 years ago, but has been inspected by ESA twice the past 10 years alone - in 2003 it was a complete change around of wiring, including relocating panel and outdoor switch.... and it's connected with a bond wire from the first barn (a 6/3 cable with bond), and no ground electrode.... by a separate contractor as the other....

sprdave

Makes sense if the utility side is grounded and service side is grounded....assuming there is neutral current to carry

RIVETER

The neutral should be physically connected to the grounding means only at the service disconnect. If you want to create another grounding means at a remote location, you can do that but you cannot tie it to the neutral.

xlink

I don't understand the description.

If the panel isn't fed with a bond, the neutral must be grounded. If it's fed with a bond, the neutral must not be grounded. It must have either a bond in the feed or the neutral must be grounded, but it can't have both.

xlink

In a city where the water line is conductive, the water line is a second path for the neutral, through the neighbours' houses. The current can be significant but it's unpredictable because it's parallel with the neutral but a longer route so a higher resistance. Additionally, you can't tell whether the unbalance load is from your panel or from all your neighbours.

AHA! I just figured it out. About a year ago I was at a house that had significant current and voltage on the water line. It shouldn't have been there because the neutral was solid right back to the pole. The neighbour must have a faulty neutral and their unbalanced load is feeding back through my customer's house.

RIVETER

Maybe you know what you mean, but I don't. Panels are not fed with a bond. It is created later.

sprdave

uhhh, now Im confused...I thought I was getting it figured out...

Oh wait, you're not in Canada, is it different in the US?

It has NEITHER. It is NOT fed with a bond. It has a ground electrode but NOT bonded to neutral

That just seems wrong to me (to allow that)...with all the specifications/codes/details we go through and have this happening?

sprdave

I do, means that a bonding conductor is ran with the feed conductors to the subpanel (2 hots, 1 neutral, 1 bond)