ECN Forum Forums Code Related Discussion NEC & other Code issues Sub-Panel

"I learned fast that just because the contractor does not do it like I do means it is incorrect."

Is that a typo? If not, I am glad you don't work here... Is there a failure of coffee and donuts being provided?

Not trying to be disrespectful, but the code is not always cut and dry. There are options to design, and for the most part conditions for them. Just because one way is more common, does not automatically mean its wrong. I keep a code book in my truck, (As we all should) but often will have it hand for an inspection if I have a vaguary, or something un-orthodoxed. Not that this particular situation is. (You can also be guaranteed I checked before I installed it.) The code book also makes a good backing when they sign my card, but also if there is any question, its right there. Most Inspectors don't have any problem with me handing to them when they question something. That said, I have had only one red tag, (Not my fault) in 15 years, other than prefferential corrections requested by Inspectors. Which, I technically did not have to do. Most Inspectors here will often sleep on it, and not give any tag or a temp, unless it it is totally obvious, and un-disputable. Even willing to bring the card, and pick up the tag from you. Anyway, not saying I'm never wrong, (And I have been at times) but if it's right, expect a debate of some kind. "Do you take suger and cream in your coffee?"

Now there is a statement that can be interpreted as meaning two different things, depending on how you 'pause' when you read it. Joe has definitely been reading codes for a while as he has taken on code writing style.

No offense meant Joe.

Just curious, I'm actually on a job where I am running 4 wires because the only place where the ungrounded conductor and the ground can be bonded is in the main panel (service entrance). Any other location to panels downstream the neutrals and grounds have to be separated to avoid loosing a neutral and the ground picking it up and carrying it back to the main panel or creating another path. How could you treat this as a separate service and only run three wires?

Ky the "open neutral" scenario is not the reason for the rule about regrounding the neutral. They just don't want voltage gradients within the building. When you get to the next building, with a new ground electrode system, you can start a new "pseudo service" regrounding the neutral ... as long as you don't have a bonded metalic path back to the previous building.
The ramifications of an open neutral in building #2 are exactly the same as one in building number one.

That is not entirely true. There are a few instances where you may be allowed or required to bond the grounded and grounding conductors.

Separately derived systems for one.

Separate buildings or structures for another.

Check out the option allowed by 250.32(B)(2)



The 'other path' problem is covered by this part of 250.32(B)(2)


I agree with Greg this has nothing to do with the possibility of loosing the neutral.

Why is this parallel path only a problem on the load side of the service disconnect??? There are often multiple parallel paths on the line side. What makes it safe on the line side, and under the same conditions, unsafe on the load side?
As far as using an EGC for the subpanel, in one respect it is not better. The grounded conductor will be larger than the EGC and make a better fault clearing path than using the fourth wire for a remote building subpanel.
Don

The thinking is that you are establishing a grounding system bonded at the service (or 2d building disconnect)and any ground shift would make the ground reference rise and fall with that shift. The reality is dependant on the quality of your ground electrode. That is the reason why I like the Ufer, that also catches the steel in the floor (and walls in Florida). Add the bonding to plumbing and equipment.
If you do get a ground shift from the utility grounded conductor, it will be reflected in anything you are likely to touch and you are literally the bird on the wire.

"Ground" is really a theoretical condition anyway. We measured up to 35v between buildings in some surveys we did. As soon as you start stringing other metallic paths between buildings you have to really start thinking about bonding everything to a single point. That will be the 4th wire.
In our data applications we did use a separate EGC and we supplimented it with big bonding wires run with the data lines. There ended up being a lot more copper on the ground side than what we had on the phases.

gfretwell,
Grounding really doesn't do anything to provide a stable voltage reference. If there is voltage on the system or conductor that is being grounded, it doesn't go away when you ground it. In reality, the grounded conductor that the utility supplies is not at "earth" potential if you measure to "remote earth" (earth not close enough to the grounding electrode system to be influenced by the voltage drop in the earth around the grounding electrode). The utility grounded conductor has a voltage to remote earth equal to the voltage drop on the primary and secondary grounded conductor from the source to the point where you take the measurement. There is no way to eliminate this voltage. This is the main source of stray voltage problems in pools, and the code actually requires that we energize the pool bonding grid!!!

The code rule for single point bonding has only to do with parallel paths for grounded conductor current. You are still the "bird on the wire" when there are parallel paths. Parallel paths are required by the code on the line side of the service and prohibited on the load side. The electrons really don't know what side of the service that they are on, so why are the parallel paths safe and required on one side of the serivce and unsafe and prohibited on the other side of the service?
There are no studies or data to show that useful to solve data noise problems.
Don

Don, it is not "noise" problems we fix in data when we use fat redundant bonding conductors, it is to give lightning a more attractive path than the data line.
As for the rest, we pretty much agree. The function of service grounding/bonding is to provide the equipotential reference in the building.

I also agree the NEC is silent on the utility side of the disconnect.

gfretwell,
If the lightning path is anywhere near the data lines, I don't think that additional conductor size for the grounding conductors will make any difference. You need to keep the lightning outside of the building and away from the data systems. If you have to run data between buildings you need to use fiber so lightning isn't a problem.
Don