New (2020) 250.30 Language For Parallel Generators

[yesterlectric]

Will quote the relevant text section first:
"Multiple power sources of the same type that are connected in parallel to form one system that supplied premises wiring shall be considered as a single seperately derived system and shall be installed in accordance with 250.30."

Is it the intent of this text to say that multiple generators shall be a separately derived system? Meaning it would be a violation to have a system that doesn't switch the neutral, and has the main/system bond at the main service disconnect?

 

[GoldDigger]

It sure looks that way.

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[don_resqcapt19]

No. Section 250.30 only applies if you are wiring the generator as a separately derived system. It is not requiring you to wire the generator as a separately derived system.

 

[yesterlectric]

No. Section 250.30 only applies if you are wiring the generator as a separately derived system. It is not requiring you to wire the generator as a separately derived system.

I tend to believe you though I think the text communicates something different. Some of my books are in storage right now but I went back to 14 and 17 and looked at the difference in text and couldn’t find anything that clarified the intent of the change. It seems many times they add language to the code that communicates to a reasonable person something totally different than what they intended. I think probably too many committee people working full-time jobs and then working late nights and trying to push to do the three-year code cycles instead of the five-year like the IEEE does. It takes a good bit of time to do what it takes to determine the intention by going through and looking at public inputs and comments to try to understand whether or not the text that they put down really communicates what they meant. Even if you do that you may not fully understand and even if you do fully understand what the intention was, absent a tentative interim amendment it may not even matter.

 

[petersonra]

I agree with Don. I think they are telling you multiple generators wired in parallel are a single SDS and not multiple SDS's. I also think it is horribly worded if that is what they mean.

 

[don_resqcapt19]

The following was the language in the 2014 and 2017 codes.

In addition to complying with 250.30(A) for grounded systems, or as provided in 250.30(B) for ungrounded systems, separately derived systems shall comply with 250.20, 250.21, 250.22, or 250.26, as applicable. Multiple separately derived systems that are connected in parallel shall be installed in accordance with 250.30.

The substantiation for the 2020 change says:

The present text regarding multiple separately derived systems being connected in parallel is unclear and confusing. By definition, sources like engine generators connected in parallel are no longer individual separately derived systems since each source has direct electrical connection to the other source(s). The issue is that there are many sources like engine generators, inverters, fuel cells, etc., as noted in the new informational note 3, that can be connected in parallel to form a new single “system” that is then ultimately connected by some means to the premises wiring. The revised text clarifies that it is dealing with multiple sources connected in parallel to form a single separately derived system.{/quote]

 

[yesterlectric]

It seems that this is becoming more and more of a problem with the code. Either that or I’m just paying more attention. I suggest that some of it has to do with a rather compressed three year development cycle where similar to politicians always running for reelection they’re always pushing for new code version. Nine months after it’s printed in at a time when most of the states will have not even adopted it yet and therefore a lot of people won’t have experienced any of the problems with it, is your deadline to submit a public input for a change. Then also some of the rules where someone can submit language and then it could be discussed at a first draft meeting and then I believe there are restrictions on how it can be edited after the first or second draft meeting. I recently heard a code making panel committee member discussing how he recognized language in a certain section was very sloppy but by the time he realized it which was months before it was voted on, because of the rules he couldn’t change the text.

It’s just interesting that someone wrote a proposal saying that the language was confusing and it resulted in another set of text that is also confusing.

 

[don_resqcapt19]

There are restrictions as to what can happen at the comment stage. New material cannot be introduced at the comment stage. You can make comments to change something that was accepted in the first draft, or you can make comments to restore a PI that was rejected at the first draft.