Grounding for two service entrances to same house.

jogr · 09-23-2008, 04:24 PM

Thanks Stubbie, Very helpful post, I'm trying to digest everything in your post.

Quote:

Originally Posted by Stubbie

What you have is a site isolation device which is covered in NEC 547, specifically 547.2 and 547.9 and related sections. The pole is your distribution point and is commonly called a farm yard pole. This belongs to you not the power company.
It is not your service disconnecting means these are located at each structure and panel ..gec systems installed at each structure. It is one service as you suspect. Grounding and bonding is in accordance with 250.32. In your situation an equipment grounding conductor was not run with the service entrance and that is fine as long as neutral to ground bonding occurs at the service equipment enclosures with the grounded conductor and no other metallic paths exist. A gec is also required at the pole.
I'm pretty sure I understand the above and what you describe does fit my situation. There is a gec at the pole and no equipment grounding conductor from pole to house (3 wire rather than 4). No paths of metal conductance between post and house. Overcurrent protection and disconnect are provided in both panels in the house. The 100 amp panel has bonding between the neutral and ground bars and there is a ground wire to the water pipes and to a ground rod driven into the ground at the house. The 200 amp panel appears to have no ground which baffles me - I'll have to look at it again.

The 200 amp panel used for the dedicated electric furnace was allowed under different application or uses from the yard pole.
I'm not totally following this. The 200 amp panel is also fed by feeders (I think I'm using the term feeder correctly regaring a 547.9 yard pole setup but maybe not) from the yard pole. So it's not sinking in what you mean by "allowed under different application or use". Are you saying that the local AHJ allowed a deviation from an NEC section for this or is there another section of NEC that pertains to differnt applcations?

Your problem is you want to use the second 200 amp panel for your dwellings addition and as such it is served by service conductors not a special application. I'm missing it again, difference between special applications and service conductors and also confused about what to call the conductors from the pole to the house in a yard pole setup - feeders vs service conductors etc. I would have thought service conductors but 547.9 seems to call them feeders and I'm not sure of the ramifications of either name in this case.

You cannot have two services to a single family dwelling... at least not in your situation. But I thought we established I only had one service and that service point was at the pole. Does the presence of a second panel in parallel at the house make it two services even though I only have one service at the pole? I get it that if they were in series then the second panel would be fine set up as a subpanel as you later mention as an option. The NEC seems to be silent on the subject of splitting one service in parallel to two panels on a single family dwelling but does mention it and allow it for duplex/multifamily.

And I don't think the poco will welcome hanging another meter on the pole. No need to, both panels are currently downstream of the meter.
If the pole was set up for feeders with disconnecting means (service equipment) located at the pole you could do what you want. A disconnect for each set of feeders rather than the one there now for all feeders together?

this would be no different than a 400 amp service to a dwelling where two sets of service entrance conductors are ran from the meter to the 'service equipment' and then to two panels in the home. The service to the pole now is likely 400 amps as it use to run several grain bin blowers as well as the buildings so it sounds very similar to this condition. I'll need to look into this more. When 400 amp service is run to 2 200 amp panels is a grounded neutral conductor (3 wire) used between the service equipment and the panels or is an equipment grounding conductor (4 wire) used? If two sets of service entrance conductors are run from the meter to the home can the 2 panels function as the service equipment if they are located at the point of entry to the building?

Since your service equipment is not located on the pole I don't believe you will be allowed to use the 200 amp panel as you described. You could however use it if you disconnect the service to the 100 amp panel and run a sub feeder from the new 200 amp panel to the 100 amp panel or use a feed thru lug panel for your 200 amp arrangement. all this subject of course to the local jurisdiction.

Using the 100 amp panel as a subpanel is definitely an option. My biggest concern is the difficulty in appropriately removing the extra conductors from the house to the pole. Especially if there is a legitimate way of maintaining both panels in the event I would want to go all electric in the future.

Thank you all for your patience in walking me through this unusual setup. I want to do this right and am in an unusual circumstance where the AHJ is telling me that no permits or inspections are required. I described the situation to him and his response was that if I already have service entrances to my house I can replace the panel and add circuits to my hearts content as long as I don't upgrade either service to more amps (it's a rural farm thing). But I don't want this to bite me down the road if I ever sell and I certainly don't want any saftey issues.

Stubbie · 09-23-2008, 08:17 PM

Jogr

What you have now is no overcurrent protection at the pole, Junk went over this, you have unfused service conductors to the panels on the dwelling and other buildings. Except for the 200 amp panel it is not considered a service disconnect. Those panels enclose the service equipment as the main breakers are the service disconnects at each of your buildings. If you had feeders to the dwelling and other buildings you would have service disconnects/overcurennt protection for each building and your dwelling located out at the pole (grouped disconnects).

The 200 amp panel I understood to be dedicated for electric heat, so I'm picturing a panel with breaker(s) for only the electric furnace when you were using it. It does not have breakers for anything else other than a main breaker? The ahj will allow a feed to a special machine or appliance such as the heater for your home from the pole. It could be that the absence of a grounding conductor is due to the use of metal conduit or metal flex to the heater from the panel. In which case they are using it for the equipment ground. My best guess is that the inspector allowed the unlimited tap rule to power this panel and electric furnace by connecting at the meter can lugs.

In order for the feeds from the yard pole to be classified as feeders they would need to originate from service disconnects used as the overcurrent protection. In which case you would have service entrance feeder conductors not unfused service conductors. In other words feeders are load side of the service disconnecting means.

Now as to the question of 2 services. You only have one service at this point. However if you convert the 200 amp panel to serve branch circuits for your addition you now have a panel that is not special in its application but is in common with the same use as the 100 amp panel. This makes for two sets of service conductors to the house for the same common purpose and is not allowed because the conductors are not service entrance feeders. If you had two service disconnects at the pole and feeders ran to each panel then I believe it would be allowed as I see things from here. Farm yard poles are kind of a different duck than most so you best check again with the inspector. In general if the meter is located on the dwelling and the service disconnect is also located there you can have two feeders to different panels with 400 amp services. From outside points...ie..a power pedestal or something similar like you see for mobile homes you can only have one feeder to the dwelling...period. So I'm not 100% sure about two feeders from the farm pole even if the meter and service disconnect is located there. I'm having no luck finding substantiation in the code book. But from experience I'm pretty sure that with farm poles classiedfied as distribution points under Art.547 it will be allowed to run two feeders. But I sure can't find it in the book.
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You will have to clarify with your ahj or inspector. Sounds like they have given there blessing but I cannot see how they are allowing another service panel on the same dwelling when it is not fed from a service disconnect. Again maybe somehow they are using the unlimited tap rule from the farm pole.

The disconnect at the pole is not a service disconnect it is there for maintenance, and emergency purposes and usually provides for a means to connect standby power in the event of a long power outage.

And yes you have a 400 amp service with 320 continuous amp rating as evidenced by the CT monitoring at the pole.

jogr · 09-24-2008, 10:31 AM

Thanks Stubbie, it makes sense to me now. This has been tremendously helpful in understanding what I have. I'll have to have a detailed discussion with my AHJ.

Stubbie · 09-24-2008, 11:31 AM

Your welcome. I wish I could pin it down for you but unfortunately just haven't been around the block enough in your situation to be comfortable in stepping on one side of the line or not....

EDIT: I noticed all the other guys responding must be working......