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NFPA 110: Standard for Emergency and Standby Power Systems extended Q&A


Recent Consulting-Specifying Engineer webcast presenters Tom Divine, PE, Project Manager, Smith Seckman Reid Inc., and Kenneth Kutsmeda, PE, LEED AP, Jacobs Engineering, answer reader questions about what new code requirements will mean for consulting engineers.

Q: When is it required to have a 3 pole and 4 pole ATS?

  • Tom Divine: When the generator is a separately-derived system, a 4-pole ATS is required for circuits with a neutral.  If the circuit has no neutral, a 3-pole ATS will suffice.  The purpose of the requirement is to avoid multiple connections between neutral and ground, which could provide alternate paths for neutral current, and cause improper operation of ground fault protection for equipment.

Q: With respect to breaker coordination; what are the preferred electronic trips: LI, LS/I, LSI, or LSIG?

  • Kenneth Kutsmeda: LSI or LSIG are preferred because they provide the most flexibility when trying to coordinate.  If you are trying to serve Article 700- or Article 708-type loads, pay careful attention to the selective coordination requirement when selecting trip units.

Q: Do you recommend dual hot-standby control PLCs when installing parallel gensets?

  • Kutsmeda: Yes, if the project can afford the additional cost, I would recommend dual control PLCs.  This prevents the PLC from becoming a single point of failure.


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