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I bought a house in Massachusetts (USA) that was built around 2009. It has a generator with a service rated automatic transfer switch (ATS) connected to a main panel that is set up as a main panel (NOT a sub panel). I don't know if the generator was there from the start, or added later.

Everything I have read seems to indicate that my main panel should be set up as a sub panel with neutrals and grounds separated, green neutral bond screw removed, and the GEC + all bonding should take place in the ATS panel. None of this is currently the case.

I'm wondering if this is or ever was code compliant? I have an inquiry out to my town's electrical inspector. I was hoping to also get feedback from the great minds of the internet!

Note that my grounding electrode is my copper water pipe and there are no ground rods by the service entrance. My meter is up at the street ~200 feet away from the house. The meter has ground rods, bonds ground and neutral, and has a 200 amp breaker in it. Three wires run to my house (2 hot 1 neutral) in underground PVC conduit. My inspector confirmed that everything in this paragraph was inspected and met code when inspected in 2009.

Here is a diagram that I made of the current configuration of the ATS + main panel:

Main Panel and ATS configuration

Update 1/20/22: Here is a photo of the ATS labeling on the door as requested by @ThreePhaseEel:

Picture of ATS label on inside door

Update 1/23/22: The model number for the Briggs & Stratton ATS is 071025 (rev 00)

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    Good question. Yes, it pivots on a) on when NEC changed that requirement, and b) when your state adopted that version of NEC. Jan 17 at 19:24
  • Who is your electric utility? Jan 17 at 23:50
  • My electric utility is National Grid
    – kr4sh2
    Jan 18 at 0:11
  • Can you post photos of the labeling on your transfer switch please? Jan 21 at 3:35
  • @ThreePhaseEel I just added a photo of the labeling on the inside door of my ATS. I think there are also labels on the inside walls of the panel as well. Let me know if those are relevant and I can snap a pic this weekend.
    – kr4sh2
    Jan 21 at 3:51

1 Answer 1

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Your jurisdiction had not adopted the 2008 NEC when this installation was made, presuming that your service disconnecting means is located within the pedestal at the property line

What you have, provided that your utility agrees that the meter pedestal/post/rack at your property line is indeed your service equipment, is the "service dip" (underground service from overhead distribution) version of a rural "maypole" configuration, where a single metering point is designated on the property, and service entrances or feeders are run from there to the various outbuildings present. Given that you have a disconnecting means at your metering point and that this is recent construction, the wiring from it to your house is a feeder in all likelihood.

With that out of the way, were this to be built today, said feeder would be required by the NEC to have a separate equipment grounding conductor pulled with it, with the neutrals and grounds at the house's panel separated and the neutral bonding screw in that panel removed. However, in 2009, there's a chance that your jurisdiction had not yet adopted the 2008 NEC, which is the edition that deprecated grounding outbuilding feeders via the neutral, relegating it to an exception exclusive to existing installations. So, this could very well have been to local/state Code at the time it was inspected, although it would not have been to Code any longer after the AHJ's next adoption cycle took place.

That said, it's unclear in your configuration precisely where the bonding means for the building should go. Converting this to current Code, however, is not recommended, because it creates a single-point dependency on the integrity of the neutral-ground bond at the remote service equipment, and bonding the neutral of a stationary generator is not compatible with the transfer switches typically used in light-duty applications like yours. In particular, if your feeder was completely severed, resulting in a transfer to generator power, then since your generator's neutral is (and must be) floating, with a four-wire feeder from the pole to the house, there would be no neutral-ground bond in the system at that point, leading to a shock risk.

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  • If someone can come up with a way to bring this up to current Code standards without incurring the risk of a floating system if the feeder is completely severed, I'd like to hear it! Jan 24 at 4:35
  • I understand what you mean by the shock risk if my 3 wire feeder were to be converted to 4 and there being no neutral+ground bond in the system if the feeder was severed. A SDS generator/ATS that bonds neutral and ground + switches neutral would solve that if I understand correctly (very expensive I think?). I'm wondering if there is a middle ground in regard to the ATS and the main panel. Could everything after the ATS could be 4 wire feeder, while keeping the 3 wire feeder to my ATS. Then bond everything in the ATS. If that improves anything?
    – kr4sh2
    Jan 24 at 8:09
  • @kr4sh2 given that the ATS is right next door to the house panel, moving the bond to the ATS doesn't change much about your setup (save for having to separate neutral and ground in the house panel itself), and yes, a SDS generator + switching neutral ATS would solve the issue, but at the cost of a rather more expensive ATS unfortunately Jan 24 at 12:32
  • It seems so weird how the current code is so specific about where to bond neutral and here I am with 3 disconnects between the street and where my main panel bonds neutral again. I get it though... this is pre 2008 code across the board with the 3 wire feeder. Since non-SDS generator setups are common for residential, is the severed feeders situation not a worry for others because most people have the meter on their house versus mine is far away and subject to more potential hazards?
    – kr4sh2
    Jan 24 at 15:45
  • @kr4sh2 -- exactly. most people have the service disconnect on their house with its attendant neutral-to-ground bond, so the situation where a dropped feeder could sever the N-G bond while the generator tries to power the house up without it via the transfer switch isn't a concern for them Jan 24 at 23:28

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