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Thursday, April 7, 2016

Question:

Does the Critical Branch feeder breaker require separation from normal and optional breakers and the wiring in a switch board on the line side of the transfer switches that are being fed from the hospitals generator? It is a larger system (well over 150kva) with multiple transfer switches’

Thank you for your help again, Jim Dorsey Electrical Inspector

A

Answer:

Hey Jim thanks for your question and you are welcome. I believe it is not required to be done (although it might be a good idea) but it is required to be considered, based on the wording in 517.35(C). Only the life safety branch is required to comply with Article 700 as stated in 517.26. The critical branch must be kept entirely separate from all other wiring and equipment as stated in 517.30(C). Looking at Figure 517.30, No. 1 the essential electrical system is comprised of the three branches which is stated in 517.30(B) but does not appear to include the transfer switches. An additional sentence is expected for the 2017 NEC that will state "The division between the branches shall occur at transfer switches where more than one transfer switch is required. Check with the Hospitals Governing Body to make sure they agree with this interpretation.

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