Right, but their internal reference to resolve their lack of clarity is the document we are talking about. So you only have a problem if you need them to recognize what the document says, and after consulting the document they still disagree.
That is true - I have it in writing, and all I need. Though I'm thinking more about how broader humanity is impacted. I'm only mentioning the below rant, as I'd value your below input if you think there is a valid NEC PI submittal, coupled with a reach out to Xcel senior management. I awoke early yesterday thinking... wow, this is a massive knowledge gap that affects customers, and possibly safety... there must be a way to improve this.
Here's what I experienced:
Xcel Contractor: The designer offers 3 times to upgrade my service to 400A, and the tech who came on-site said the same thing. With both, they seemed to go quiet and be searching their head, followed by an awkward moment of silence when I mentioned 320A service is good for 400A. The designer reaches out to her 'electrical engineer', who punts and says I should defer to my electrician for sizing of the meter. Her supervisor says 'we only offer 200, 320, 400A service' in response to confirming my request to confirm that the Xcel owned components of the service are good for my calculated 374A.
Xcel: Prior to working with the Xcel contractor, a guy with the title 'Specialty Engineer' who works in the 'meter shop' can't confirm to me that 320A service is good for up to 400A non-continuous. Eventually I find that excerpt from the Xcel install guidelines doc and send him a screenshot, to which he responds to a screenshot from the same doc that mentions 320A service disconnects cannot exceed 400A combined.
Electrician: Tells me a 320A meter can only handle 320A. Clearly built the service on that, undersizing the service entrance conductors and limiting my service to 350A (potentially 373A). My guess is a number of electricians have spoken with folks at the POCO and that is where they got their education that the meter is only good for 320A.... shouldn't question the POCO, right? They're generally not going to invest the time to prove to the contrary, and now for the rest of their career, max capacity of 320A drives their work. Furthermore, if one takes the trade forums as some indicator... it seems even the electricians knowing that 320A service can support up to 400A non-continuous aren't able to clearly articulate what the determining/driving factor would be in selecting 400A service (vs 320A service) for a residence. Though, that could be a misread on my behalf. Funny thing is that same electrician over-spec'ing a service which will run thousands of $ more, will be trying to trying to talk a homeowner out of having 20A general use receptacles because it's an unnecessary cost.
I'm not sure if there are direct safety issues that could stem from the assumption of the more conservative rating (you'd have a better feel for that), other than the fact that some notable 320A services will have undersized conductors. That could lead to to some future misunderstandings about the service's capacity and overloading of the service if conductor sizes isn't checked... but that ambiguity is more a risk of the NEC's rules, anyhow.
However, from a waste perspective, it's huge and real. Both money and resources. I paid $6k for the 320A service upgrade (pre-Covid) and now POCO suggests I go to 400A 4 times? Beyond that, they (and electricians) are over-specifying services at 400A, when it's not required and it is definitely more costly than 320A service. If I wasn't the type to dig in (and not many homeowners have spent hundreds of hours reviewing code), I'd have no reason to disbelieve any of the above persons. But, this can be fixed on both the Electrician (NEC) and POCO side (Education).
Obviously NFPA wants to keep NEC from growing any more burdensome and overweight than needed. Do they ever approve PIs that add clarity, but maybe not safety? I can imagine a table that shows class of service, and the associated allowable continuous and non-continuous loads.
Anyhow, call me crazy, but I feel the industry can do better than all this waste and confusion. 320A service is only going to become more common.
I figured, that is definitely the conventional wisdom. The typical marginal load in the optional calc gets a factor of 40%, while the typical marginal load in the standard calc gets a factor of 100%.
Who knows how I messed up the calc so badly, but at least it put me in a better position.
Correction, you have no 180A service conductors; your 4/0 Al are feeders. And as partial feeders (not carrying the entire dwelling unit load), they can't use the optional method.
So for the SECs you have the choice of the optional or standard method; every downstream segment must use the standard method just for the loads it serves.
*sigh* I even went to the extent of looking up the definition of service conductor, but misinterpreted the disconnect to be my main breakers, and not the meter disconnect. Thanks for setting me straight. Feeders it is.
Excellent question, it is not defined and is a source of ambiguity. See, e.g.
Contractor has a 320 meter feeding into a 400 amp transfer switch with 400 amp main breaker double tapped parallel 4/0 al se cables off of load side of breaker and runs 25’ to two 200 amp panels with main breakers. Would I be wrong if I said that This is in violation of 240.21 (B2,2) Where it...
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Let's say we have a residential service going to a Class 320 meter/main with (2) 200A OCPD. 230.90(A) Exception 3 says that the SEC ampacity only needs to be at least the calculated load, not necessarily a full 400A. And 310.12(A) says the SEC ampacity only has to be 83% of the "service...
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The latter is entirely on point for your situation and inspired by it. Worst case for you, "service rating" has to match a standard OCPD size, meaning that your SECs are only good for 350A. But since you can use the optional calc for them, that shouldn't be a problem.
I'm honored you would go for clarity, inspired by my topic. Thank you very much. The timing of that any my definition question is a little funny.
I read through those threads, and with a little brain squeeze was able to track most of that, but not 100%. It sounds like there is an interpretation question that is likely to get different answers, depending on who you talk to, and that the more conservative answer would be to call my service 350A. I, too, had looked at table 310.12(A) and like jaggedben had interpreted it to be used optionally, versus restrictive... however, that was just my guess. But, I can mostly understand the other areas of ambiguity mentioned and the reasoning.
100%. Article 220 doesn't deal with continuous vs non-continuous at all; you have to track it separately when doing the Article 220 calculations. That's because other article that reference loads (which have to be calculated via Article 220) do reference continuous vs non-continuous loads, so you need to know the breakdown.
So it goes like this (made up example):
Sorry to have been pedantic on this, and not really a question of your knowledge (clearly this code is engrained in your head), but trying to understand why it isn't laid out more clearly, and what the value of a load calculation is, if the resulting value can't be used directly. The only possible use case I could think of for the load calculation without directly including the continuous factor might be the sizing of the meter, but I'm not even confident on that... or maybe I've missed some bigger use.
Might sound a little odd, but I feel like NEC needs to undergo a fundamental re-architecture.
How large do you think fiscal value would be if NEC was replaced with something that easily allowed an electrician or other industry professional to reliably get an answer as to how a scenario should be handled, without having to dive directly into the text, thus driving up compliance and down safety issues?