What are the requirements/guidelines for coordination studies? 4

[tivester]

Is there a requirement or guidline for performing a new coordination study/short circuit analysis when a facility's existing electrical system has had changes and additions made to it? While I assume it is best practice to do this, is there a section of the NEC, NFPA, or IEEE standard that specifically references this requirement? Thank you.

 

[rbulsara]

NEC only 'requires' the coordination study for emergency systems AND other systems where there is a safety issue related to people and process. See 240.12 and articles 517 and 700.

It is important to note that codes like NEC are only concerned with safety and not with minimizing production or monetary losses or inconvenience to the owner. For example, the code is happy as long as a breaker trips and clears a fault, whether that breaker be the building main or a branch breaker.

It is up to the end user to decide (and people advising them) as to what is in their best interest. If they want to limit the outage to faulted area only, they should have a coordinated system, as best as possible.

Code also does not prescribe exact procedures, but there are recognized procedures in standards like IEEE (Red Book)and IEC standard 60909.

Coordination study goes in hand in had with short circuit study and NEC 110.9 and 110.10 requires that. Also there is a good article in the latest EC&M magazine, on the SCCR subject and NEC.

Rafiq Bulsara

http://www.srengineersct.com

 

[tivester]

Are you refering to the Commercial Loads article in the January 2010 issue?

 

[caporter]

The 2009 NFPA 70E section 130.3 requires an arc hazard analysis be done at every major renovation or modification, and periodically not to exceed 5 years. Short circuit and coordination studies are part of that. The section states the design of the protective device, it's opening time and condition of maintenance shall be considered to account for changes in the distribution system that may effect the results of the arc hazard analysis.

The exception is for branch system off a single transformer 125 kVA and 240Vac or less.

 

[rbulsara]

tivester:

It is in the February 2010 EC&M issue, "The SCCR Liability Trap" article.

Rafiq Bulsara

http://www.srengineersct.com

 

[alehman]

Coordination is also required in NEC 701 and 708. Be sure to give some thought to the NEC's definition of Coordination (Selective). This is a touch subject. Some code authorities have misconstrued it to apply to every pair of overcurrent devices, regardless of potential impact.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[RRaghunath]

See IEEE141 (Red book) / Sec. 5.1.3. It may be relevant.