Mr. Benjamin Medich had a recent article published in CSE magazine (Sep. 2012). The subject of the article was sizing equipment for closed transition operation. In the article he presented a rationale supporting the notion that fault contributions of all parallel sources must be considered only for systems designed for continuous parallel operation. The conclusion was that there is no need to consider both sources of fault current when sizing equipment for closed-transition transfer schemes. The summary of the article is presented below:
"Based on a review of applicable codes and standards, there is no need to consider both sources of fault current when sizing equipment for closed-transition transfer schemes. However, when making this determination, it is important that the proper electrical interlocking or other supervision techniques are used to ensure that the system cannot be inadvertently placed into a maintained parallel state, which would require that the equipment be sized for the combined parallel sources. This will assure a safe, cost-effective installation that complies with NEC requirements, and is consistent with IEEE guidelines."
I am interested in hearing contrary and supporting opinions.
"Based on a review of applicable codes and standards, there is no need to consider both sources of fault current when sizing equipment for closed-transition transfer schemes. However, when making this determination, it is important that the proper electrical interlocking or other supervision techniques are used to ensure that the system cannot be inadvertently placed into a maintained parallel state, which would require that the equipment be sized for the combined parallel sources. This will assure a safe, cost-effective installation that complies with NEC requirements, and is consistent with IEEE guidelines."
I am interested in hearing contrary and supporting opinions.