Quick Hits

Episode 5: Power Source Portfolio—Generators, Batteries, and Microgrids (700.12)

Emergency sources must have sufficient capacity to carry the total load for at least  2 hours.

The Source Breakdown

• Generators (700.12(C)):  Must have on-site fuel for 2 hours and independent battery chargers. If the generator is outdoors and has a disconnect within sight of the building, that disconnect can serve as the building's main emergency disconnect.

• Storage Batteries & UPS (700.12(B)(4)):   Do not use automotive-type batteries.  They are designed for short bursts of high-cranking current. Emergency systems require deep-cycle batteries capable of sustained loading for  1.5 hours without the voltage dropping below 87.5% of nominal.

• Microgrid Systems (700.12(F)):  These must isolate emergency sources from non-emergency loads during a failure to maintain the 2-hour duration mandate.

• Unit Equipment (700.12(G)):  Must be permanently fixed. The branch circuit breaker must be equipped with a lock-on feature to prevent accidental disconnection.

Episode 6: Emergency Illumination and Control (700.15 - 700.28)

The "Total Darkness Prohibition" (700.16(B)) is the gold standard. The system must be designed so that the failure of any single illumination source (like one bulb blowing out) does not leave a required area in total darkness.

System Reliability Features

• HID Lighting (700.16(C)):  Because High-Intensity Discharge lamps have a "warm-up" period, the emergency system must stay on until the HID reaches full brightness. Use auxiliary LED or Quartz lamps to bridge this gap.

• Directly Controlled Luminaires (700.24):  If luminaires are dimmed, they must be listed for emergency use and be designed to default to  "Full On"  during an emergency.

The "So What?" Layer

Understand the  Automatic Load Control Relay (ALCR)  (700.26). While useful for energizing loads, an  ALCR is NOT a transfer switch. It does not have the mechanical interlocks or undergo the rigorous UL 1008 fault-current evaluation required of a transfer switch. Do not use it to switch between two non-synchronous sources.

Episode 7: Overcurrent Protection & Selective Coordination (700.30 - 700.32)

Selective coordination is non-negotiable (700.32). In an emergency, we want the branch circuit fuse to blow, NOT the main generator breaker. If a fault occurs in one room, the rest of the building must remain illuminated.

Selective Coordination Analysis

• Mandate:  Coordination must be achieved with all supply-side and load-side OCPDs.

• Documentation:  This must be performed and documented by a licensed professional engineer.

• Maintenance:  You must re-evaluate coordination every time you modify the system or replace an OCPD with a different model.

The "So What?" Layer

Compare the  Ground Fault requirements (700.31). In standard systems, ground faults trigger an automatic disconnect. In Article 700,  automatic disconnection for ground faults is PROHIBITED  for the emergency source. Instead, you provide "Indication" (700.7(D)). We prioritize keeping the lights on over protecting the equipment from a ground fault during an emergency.

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