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#217121 - 05/10/16 01:50 AM Help! New Grounding and Bonding Requirements  
twh  Offline
Member
Joined: Mar 2004
Posts: 916
Regina, Sask.
The electrical inspection department in Saskatchewan has now mandated in its 2015 Interpretations that the neutral shall be grounded at the utility connection point and be kept separate from the ground, after.

This is an issue on farms where the ground point will typically be at the meter and one or more buildings fed from that meter. In the past, the neutral would be grounded at each building. Now, a ground will run with the circuit conductors and a ground rod at the building would only be connected to the panel enclosure. Every panel will be installed as a sub panel and the bonding screw must be removed from the neutral bar and the neutral conductor isolated from ground.

Because these buildings are usually fed underground, the conductors can be damaged. It's possible to lose a hot or a neutral. With the new requirement, it will be possible to lose a ground connection, too. A broken ground wire would allow the system to operate normally but the ground at the building would float.

I was taught that if the ground were allowed to float, fate would chose the conductor to be grounded. For example, a receptacle twisted in the box could cause a hot conductor to touch ground. That would bring the remote building ground along with metallic surfaces, like the panel enclosure, to a line voltage potential. Then, the voltage from ground to neutral would be 120 volts and from ground to the other hot would be 240 volts.

Is this now considered a good idea or are we just forgetting lessons from the past?


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#217141 - 05/14/16 03:46 PM Re: Help! New Grounding and Bonding Requirements [Re: twh]  
brsele  Offline
Member
Joined: Jul 2008
Posts: 91
Northern Ontario
This is also a new requirement in Ontario.

Originally Posted by twh
Now, a ground will run with the circuit conductors and a ground rod at the building would only be connected to the panel enclosure. Every panel will be installed as a sub panel and the bonding screw must be removed from the neutral bar and the neutral conductor isolated from ground.

My understanding is...
First, this is only for new installations.
Second, the secondary service would not have a ground rod installed. The panel enclosure would get attached to the bonding conductor and ground back at the CMS.
Third, this is only for buildings that house livestock. The farm house, driveshed, etc. can still have it's own ground.

Originally Posted by twh
Because these buildings are usually fed underground, the conductors can be damaged. It's possible to lose a hot or a neutral. With the new requirement, it will be possible to lose a ground connection, too. A broken ground wire would allow the system to operate normally but the ground at the building would float.

Actually my experience has been that overhead wiring is more prone to damage. But regardless I guess that our job is to try to minimize that possibility.

If this helps, here's the rational from the Ontario Bulletin that addresses this...
Rationale
"It has been demonstrated that the use of the bonding conductor run with the feeder conductors provides superior safety performance for livestock. The fact that the earth serves as a parallel path for neutral currents back to source is to be considered as a cause for stray current problems for livestock. It has been well recognized and proven that re-establishing neutral grounding in buildings housing livestock, does not eliminate problems with voltage transients and tingle voltage which has an adverse effect on livestock. Additionally, Rule 10-200 requires that grounding be arranged so that there is no objectionable passage of current over the grounding conductors. It continues by indicating where, through the use of multiple grounds, an objectionable flow of current occurs over the grounding conductor;
one or more of the grounds shall be abandoned;
the location of the grounds shall be changed;
the continuity of the conductor between the grounding connections shall be suitably interrupted; or
other effective action shall be taken to limit the current.
A current flow that causes damage to property (livestock) would be considered objectionable and therefore should be mitigated by one of the methods shown. However, this method of grounding will not mitigate the utility source stray currents."
(Hopefully I haven't broken any copyright laws by posting this.


#217145 - 05/15/16 04:44 PM Re: Help! New Grounding and Bonding Requirements [Re: twh]  
twh  Offline
Member
Joined: Mar 2004
Posts: 916
Regina, Sask.
I understand what they are trying to do. My point is that it has already been tried and it failed.

It was learned, before I went to school in the seventies, that it is better to have the neutral tied to a bonding conductor in several places than to take the chance of losing the bond connection to the source. We had the discussion in class about parallel neutral current return paths. It isn't news. It's the lesser of two evils.

So, we were taught that, even if a separate bond wire is run to the building, the neutral was to be connected to the bond and ground rods installed. A definite parallel path.

Without a separate bond conductor to the source, When the bond to source is lost, the neutral is also lost because they are the same conductor. If the neutral/bond fails, an electrician is called immediately.

With an isolated bond, if the bond fails, no one will know.

Tingle voltages can happen regardless of bonding methods. Only one causes the system to fail when the bond is lost. The cost of that protection is parallel paths for neutral current.

Imagine how dangerous it would be in a sloppy, wet environment with an isolated neutral that is assumed to be at ground potential. You could turn the equipment off to work on it and find yourself holding a neutral that has a 120 volt potential to ground, originating from a ground fault on another circuit.

The floating bond will also be connected to watering bowls, rails, gates, the machine that scratches the animals backs and the one that holds the animal so it can be cared for. Imagine the financial cost to my dairy customer if their 400 cows were afraid to enter the milking machine. What we have is working. Don't change it back just because current over a ground conductor is "undesirable". At a minimum, I can make sure the inspectors messing the the rules can't say they didn't know. I'm telling them!

Quote
Actually my experience has been that overhead wiring is more prone to damage
That's true but I have more underground to look after so repairing it is a larger part of my work. It really reinforces the understanding that wires feeding buildings fail with some regularity.


#217168 - 05/21/16 09:53 PM Re: Help! New Grounding and Bonding Requirements [Re: twh]  
twh  Offline
Member
Joined: Mar 2004
Posts: 916
Regina, Sask.
Saskatchewan Electrical Inspection Department has mandated a method intended to eliminate neutral current from appearing on ground wires.

The problem of neutral current on ground wires is most obvious when a neutral feeding a building is broken and the neutral path becomes the grounded metallic water line that ties two buildings together. This is undesirable because it puts the current from the building with the broken neutral through the other building's grounding system.

Here is the solution:

The neutrals are bonded to ground at the first connection point at each building and ground rods are connected to that point. It will usually be the meter or splitter to which the power companies runs their wires.

From the neutral bonding point, the neutral is isolated into the panel and is kept isolated in the panel. (The neutral bonding screw is removed)

From the neutral bonding point, the meter/splitter is bonded to the panel, which is then bonded to the internal metallic water line.

I have made a sketch of what it will look like with two buildings fed from the same transformer. Can you spot the flaw?
[Linked Image]



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