Article 700.28, selective coordination of EM system

[Designer69]

Article 700.28 just says that selective coordination must be performed for an emergency system and provided to inspector, AHJ etc. upon request.

Does anyone have experience with this piece, how/if it is enforced etc, or if you have done this in the past?

Thank you

 

[ron]

First determine if the jurisdiction defines selective coordination per the NEC definition (0 seconds) or modifies it to some higher time limit. Then we provide either TCC curves or manufacturer tables for each breaker pair or triplen to show selective coordination.

Sometimes the TCCs aren't enough because they do not go all the way to 0 seconds.

 

[david luchini]

First determine if the jurisdiction defines selective coordination per the NEC definition (0 seconds) or modifies it to some higher time limit. Then we provide either TCC curves or manufacturer tables for each breaker pair or triplen to show selective coordination.

Sometimes the TCCs aren't enough because they do not go all the way to 0 seconds.

Where does the NEC define selective coordination as 0 seconds?

 

[dkidd]

https://iaeimagazine.org/magazine/2...nation-for-critical-systems-per-the-2014-nec/

These revisions clarified the intent of the definition. The first change was to replace “choice” with “selection and installation”. This helps clarify that it is not a “choice” but rather the proper “selection and installation” of overcurrent devices (types, ratings and settings) that achieves selective coordination. The additional text added to the end of the definition clarifies that the term selective coordination applies to the full range of overcurrents, from overload to the maximum available fault current and all operating times of overcurrent devices for these overcurrent conditions. This added language makes it clear that “partial or limited coordination,” such as coordination for operating times of 0.1 seconds or longer would not meet the definition of selective coordination.

 

[ron]

Where does the NEC define selective coordination as 0 seconds?

I was just going to re-print the definition from Article 100, but I guess dkidd covered it better.

Some local jurisdictions and some NEC sections like 517.30(G) relaxed it to 0.1 second as opposed to generic 700 circuits.