Closed Transition AIC Rating 1

[RonShap]

I recall several NEC code cycles ago, there was a proposal made to add an clarification/exception to Section 110.9 or 110.10 where short periods of closed transition (maybe 20 ms) would not be required to be included in the short circuit calculations and the resulting withstand or AIC selections of the equipment.
I cannot locate this information or the final reply from the code making panel.
The proposal was knocked down, but I'm trying to find the actual wording from the CMP.
NFPA does not have all of the ROP/ROC's on the website. Does anyone else recall this?
What is your position when performing a study?

 

[dpc]

I'm not aware of any exception to the requirement in the NEC. I have known local AHJ's to grant a waiver based on automatic tripping of one of the breakers after a short time delay, remote control etc.

When doing a study, I consider it an NEC violation (assuming the fault duty exceeds the breaker rating, which not always the case) and note in the report.

 

[resqcapt19]

Ron,
Go to this page:

http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70

Click on "Proposals: Annual 2010 (2011 Edition) Proposals Before Panel Action" near the bottom of the page and when that opens scroll down to the Article 110 ROP for the 2002 code. I think the proposal you are looking for is 1-211.

Note to all: You can find all of the ROPs and ROC for teh 2002 through the 2008 code on this page as well as the propsals, without panel action, for the 2011 code.

 

[rbulsara]

My position is what dpc said and it is most common and correct thinking.

Plus I am not aware of a setup that will perform a closed transition transfer in 20 ms.

 

[lansford]

One of the application engineers at a manufacturer of one of the most popular transfer switch companies said you don't need to include the total contribution of fault current since it is only for a few cycles while another at the same company said you do need to include it.
(i.e. A closed transition transfer switch where the normal and alternate system is only paralleled a few cycles to insure sync then transfers)
JIM

 

[RonShap]

Don,
Thanks. It was the references to the 1998 proposal that I was thinking of, but the one you sent completely covers it as it seems to be the original writer.

 

[resqcapt19]

Ron,
The submitter of the one that I linked to is a moderator on the Mike Holt forum and this topic came up over there too. He has posted a comment on this issue at

http://forums.mikeholt.com/showthread.php?t=110459

 

[dpc]

If considering asking for a variance, I would want to make sure that the operator does not need to stand in front of the breaker being closed. Remote closing would be very desirable and should reduce the personnel risk considerably.