2017 NEC 700.3(F): ESL’s Got You Covered

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700.3(F) is a new provision in NFPA’s 2017 National Electrical Code® (NEC®) for legally required systems. It requires provisions to be able to connect a temporary source of power for emergency systems which rely on a single alternate source of power which will be disabled for maintenance or repairs. The emergency system shall include permanent switching means to connect a portable or temporary alternate source of power, which shall be available for the duration of the maintenance or repair1.

The permanent switching means to connect a portable or temporary source of power shall comply with:

  • Connection to the portable or temporary source of power shall not require modification of the permanent system wiring.
  • Transfer of power between the normal and emergency sources shall not exceed 10 seconds (in accordance with NEC 700.12).
  • Mechanical or electrical interlocking shall prevent inadvertent interconnection of power sources.
  • The switching means shall include a contact point that shall annunciate at a location remote from the generator or at another facility monitoring system to indicate that the permanent emergency source is disconnected from the emergency system. It shall be permissible to utilize manual switching to switch from the permanent source of power to the portable source of power and to utilize the switching means for the connection of a load bank

ESL’s TripleSwitch is 2017 NEC 700.3 (F) compliant when used in conjunction with an ATS.

Diagrams below represent TripleSwitch™ operating functions during various conditions.

TripleSwitch operation under normal condition


● The permanent generator is hard wired into ESL’s TripleSwitch. The output from the TripleSwitch is hard wired to the facility ATS.

● Under normal conditions the center breaker is “ON,” connecting the permanent generator to the facility ATS.
TripleSwitch operation with permanent generator running during utility power outage
● If the ATS needs emergency power, a start-up signal is sent from the ATS to the permanent generator. Once the ATS detects proper voltage, frequency and phase sequence, the ATS switches over.
TripleSwitch operation during load bank testing
● When load bank testing of the permanent generator is required, a portable (or permanent) load bank tester is connected to the load bank connection point in the TripleSwitch. Then the center breaker is turned “OFF.” Auxiliary contacts in the center breaker are wired to terminal blocks that can then be field wired to the annunciator circuit to alert personnel that the permanent generator has been disconnected from the emergency system. Next, the left hand breaker is turned “ON.” This connects the permanent generator to the load bank connection. The permanent generator can be started, and load bank testing can be done.
TripleSwitch operation with portable generator running
● Anytime the permanent generator is disconnected from the emergency system (maintenance, repairs, etc.) the annunciator circuit is activated. A separate portable (or secondary permanent) generator can be connected to the portable generator connection point, and by turning “ON” the right hand breaker the portable generator is connected to the emergency system.
  1. Source: NFPA’s 2017 National Electrical Code® Handbook

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