Fire Pump Transfer Switch Basics
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Fire Pump Transfer Switch Basics

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Fire Pump Transfer Switch Application and Design Criteria

Fire Pump Transfer Switch Application and Design Criteria

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  • 1. Power Transfer Swtiches - for - F.M. Approvals - by - James S. Nasby Columbia Engineering
  • 2. Topics to be Covered
    • Arrangement I (Combo. Unit)
    • Arrangement II (Separately Listed Units)
    • Power Supply Considerations
    • Options
  • 3.
    • Note: “Alternate Source” may be a “Hot Emergency Bus” as often employed in hospitals.
    • In these systems, multiple MVA size gen-sets are used along w/ additional upstream Transfer Switches with a path to one or more Utility Connections.
    • This often results in very high fault currents on the Alternate Source Side.
    • Also note that two C/Bs will be required in all Arrangement I units per 2010 Edition of NFPA-20.
    Two Arrangements
  • 4. Power Supply Systems
    • Power Supply
      • Weak = Voltage Drop Problems
      • Stiff = Careful Coordination of WIC
    • Type of System
      • Wye = Typical
        • Grounded Neutral = Typical
        • Ungrounded = Care & Coordination
      • Delta = Great Care Needed.
        • Ungrounded
        • Corner Ground
        • 4 Wire High Leg (240 / 120 / 208)
  • 5. Options (Varations)
    • Added Ground Lugs (Some Jurisdictions)
    • Fourth Pole (Neutral)
      • Usually “Overlapping” (Make Before Break)
      • Supplied by Some E.F.P.C. Mfrs.
    • In Phase Transfer
      • Delays Transfer Until Motor Back EMF Phase Angle is Close to that of the Intended Source
      • Completely Useless for Pump Motors due to Very Low Inertia and Large Minimum Load on Motor
  • 6. Arrangement I (Combo. Unit)
    • 10.8.1 General
    • 10.8.2.1 Arrangement I
    • (Listed Combination Fire Pump Controller and Power Transfer Switch)
    • 10.8.3 Power Transfer Switch Requirements
  • 7. Arrangement I – Combo. Unit
  • 8. Short Circuit (WIC) Coordination Note: “---” means no Upstream Protection is Required. E.g.: Self Protecting (Blow Apart) Isolating Switch Provides Suitable Protection of the Internal Transfer Switch.
  • 9. Arrangement II (Separate Units)
    • 10.8.1 General
    • 10.8.2.2 Arrangement II
    • (Individually Listed Fire Pump Controller and Power Transfer Switch)
    • 10.8.3 Power Transfer Switch Requirements
  • 10. Russelectric F.P. Transfer Switch
  • 11. Arrangement II Requirements: Who Supplies What?
    • Section 10.8.2.2(2) "An isolating switch, or service disconnect where required, ahead of the normal input terminals of the transfer switch"
    • 10.8.2.2(3) [and 9.2.3.4]: Xfer Switch OCP "shall be selected or set to carry indefinitely the sum of the locked rotor current of the fire pump motor" plus any additional connected loads. E.g.: 600% of motor FLA minimum
    • 10.8.3.4.2: transfer switch be sized at only 115% of the motor FLA current
    • 10.8.3.6.4: Phase Reversal Sensing
  • 12. WIC Coordination Example Transfer Switch Sizing Example for 100 Hp at 460 Vac X 115% Thermal X 600% Breaker WIC Coord. Motor Hp Motor FLA Thermal Sizing Upstream Size Switch Size 100 Hp 124 amps 143 amps 150 amp 744 amp 800 amp 400 amp In this Example, a 150 Amp Xfer Switch meets the 115% criteria; but, it’s Short Circuit (WIC) Rating will be invalid if the upstream device is larger than 250 amps. However, a 250 Amp OCP doesn’t meet the 600% criteria. Hence, a larger Xfer switch is needed. Who does the coordination, and who supplies what?
  • 13. Are All of These Supplied? 1) The two Position Indicator lights 2) The Engine Start delay timer and the Re-Transfer delay timer, 3) The Engine Start contacts, 4) The Test (Transfer) switch (pushbutton), maybe. 5) The Normal Side Service Disconnect and overcurrent protection fuses or breaker, 6) Otherwise, the required emergency side Isolating Switch which is: 7) Lockable "ON" 8) Having an external "Fire Pump Isolating Switch" placard, 9) A placard next to the controller giving the location of this Isolating Switch 10) Supervision of the Isolating Switch by one of the four means given 11) Audible and visible alarm to indicate Isolating Switch Open, 12) Isolating Switch contacts for remote alarm, 13) Means to prevent Higher-than-Normal motor in-rush currents, 14) Phase reversal sensing and transfer circuitry. 15) Although not required, the Bypass switch may or may not be standard equipment.
  • 14. Arrangement II Requirements
    • See:
    • Application Guide
    • - for -
    • Fire Pump Transfer Switches
    • - for use with -
    • Electric Motor Driven Fire Pumps
    • Note: An updated copy is in the handouts.
  • 15. Questions ?