Sub-panel diagrams sticky

In the Sub-panel diagrams sticky...

The diagrams all show when (and when not) to run a ground wire from the sub-panel to its own ground rod, but they don't show when a ground wire from the "first" panel should be connected to a ground rod (always?).

You may want to consider adding that connection to the drawings, or making a comment about it in the first post.

Thanks.

 

The panel with the first OCPD is always grounded. Subsequent service panels in the same structure fed by the panel with the first OCPD do not require grounding rods or electrode systems. The primary purpose of the sticky is only to provide diagrams for subpanels that can be refereed to when answering questions in the forum. I will consider your suggestion and solicit input from other mods.

 

I always wondered why they aren't drawn to match the various discussions all over the forum.

 

Can you explain more fully?

 

I'll give an example...

A couple of years ago, I found out (on this forum) that my subpanel needed to be grounded to its own ground rod. My setup is like the first diagram -- main panel in one building, subpanel in another. In fact, soon after I asked about it, there was a very detailed diagram/explanation (that was "stickied") for my scenario that's no longer there.

If I had come across the current diagram (not knowing about how it was supposed to be), and saw an EG on the subpanel but not on the main, I might have thought my old setup was backwards instead of finding out that I needed to add a EG.

 

I understand now your concern. Diagrams will be updated. Previous diagrams were removed by the original poster for editing but they were never reposted.

 

Part of the issue is depending what code cycle your location was on at the time of installation, your installation may be different that what is shown. I believe in the 2008 code cycle it was changed that in a separate structure it was required to include an equipment ground wire between both buildings. In fact, I can recall in my Father-in-laws home the electrical inspector made them remove the equipment ground that was run.

In a "normal" main electrical service installation, the main ground is to the water pipe. The ground rod is a supplemental ground.

 

As just mentioned it was in 2008 that the NEC required an equipment ground to be run with the feeders to separate buildings or structures, 250.32(B). Since so many installations exist that were installed prior to 2008 it may be good to include a diagram for existing installations. The 2008 NEC, while requiring the equipment ground, did not mandate any changes to the existing installations. People will still find feeders without the equipment ground and they are still allowed to have the neutral bonded to the disconnect at the separate building.

 

It may be the subject is to complicated for a few diagrams.

 

First two diagrams modified. Comments welcome.

 

Looks good, that should eliminate some confusion for those not familiar with proper grounding. Thanks for making the changes so quickly.

 

More to follow. I am not sure on the transfer switch if I should show a ground between the switch and inlet. I'm a bit out of my depth there. That was why I originally didn't draw one.

 

Ray, there would be a ground between the generator and the transfer switch. The issue with generators is when the neutral is bonded to ground at the generator and when it is not. On a residence the service neutral is bonded at the service and not at the generator because the neutral, is not switched with the transfer switch, so the generator is not considered a separately derived system. The generator neutral bonding to ground is at the service equipment. The bonding jumper should always be checked at the generator because they often come bonded to ground and may need to be removed. The generator frame still needs to be grounded.

 

Thank you all for your input into this thread.

 

Just curious here,
If the neutral bus bar is bonded to ground in the main entry box, and you ran the ground from feeder panel or sub panel, ground bar to the main service panel ground bar, would that not achieve the same result?

Thanks,

 

The newly-added Bahtah diagram conflicts with the previous diagrams. Can you give an example of when a sub panel in a detached building should be bonded?

 

As it says at the bottom of the diagram that is pre 2008 code. So yes if it is grandfathered and there were no other metallic pathways at the time of installation then Bahtah's diagram is correct.

 

Bonded to what?

It sounds like we may be starting to confuse grounding with bonding. That's a common bit of confusion, and can lead to misinterpretation and misapplication of requirements - especially since the NEC often uses the terms in an unclear manner. I'm not saying that's what you're doing, Guy, but it's where we could go if we don't take a minute to clarify the difference, and how that difference applies here.

Mike Holt's comment on Grounding vs Bonding is a starting point for this.

So, here's a quick-and-simple bottom line explanation that may help clarify this question. I hope so:

The utility neutral, the branch circuit neutrals and the branch circuit grounds should always be bonded together and to a grounding electrode (embedded in the earth) at the service entrance. As Tolyn noted earlier, the primary source of earth ground is normally the incoming water pipe, and any ground rod(s) are supplemental. This bond establishes - creates - is - the grounding electrode conductor.

Beyond that point the grounding conductors (ground wires) and all metal service equipment need to be bonded together to keep the low-impedance fault-current path intact and complete. All grounded conductors (all neutral wires and terminals) need to be isolated from the grounding. I.e., they must be prevented from contacting any part of the ground path, including enclosures (boxes). This is required so that high-voltage transients (lightening surges, e.g.) do not find a low-impedance path into and through the structure

The neutral-to-ground bond in an emergency power generator feeding a structure must be defeated or disconnected in order to eliminate one such low-impedance path. It must also be defeated or disconnected in order to eliminate the possibility of backfeeding power to utility conductors that are under repair. That's a critical issue, but separate.

The provision of a secondary low-impedance path to source (earth) at a detached structure is, as others have said, a relatively recent requirement. That said, it should always be provided in all new installations and upgrades. And, as with all other locations beyond the service entrance, only the grounding conductors - including the one from the supply panel, if that exists - and the enclosures should be bonded to it. All grounded conductors must be isolated from it.

Ray, does this help you in your quest to tune up the diagrams?