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Service Entrance Specifications

The ASCO Service Entrance Automatic Transfer Switch combines automatic power switching with a utility circuit breaker as a disconnect device. The power transfer switch meets all National Electrical Code requirements for installation as service entrance equipment.

The ASCO 300SE Service Entrance Automatic Transfer Switch uses the same reliable transfer switching mechanism, and controller as the series 300 product platform and also includes a utility circuit breaker as a disconnect device.


  • Suitable for use as service entrance equipment.

  • The ASCO Series 300SE (service entrance) is listed to UL 891 standard for Dead-Front Switchboards, and meets all NEC requirements for  equipment.

  • Automatic Transfer Switch is listed to UL 1008 for total system loads.

  • Sizes available from 150 through 3000 amps.

  • Available to 600 VAC, 50 or 60Hz, single or three phase.

  • Circuit Breaker disconnect on the normal for isolation of transfer switch and other electrical equipment.

  • Disconnect link on Neutral and Ground.

  • Silver plated copper ground and neutral bus.

  • Solderless screw type terminals for External Power Connections.

  • Ground fault trip protection provided on sizes of 1000 amperes and above.

  • UL approved Type 1 enclosure.

  • Available with solid or switched neutral.

  • Motor load transfer controls (in-phase monitor) to keep motors operating during transfer.

  • Pre-transfer & post-transfer load disconnect contacts for signaling motor starters, elevators, VFDs and other selected loads.

  • Standard Engine Exerciser for weekly automatic testing of engine generator set with or without load.

  • Selectable control switches for voltage, frequency, time delay settings & additional control features.

  • Switch position lights, source availability lights, test switch and time delay bypass switch.



  • Adjustable time delay to over ride momentary normal source outages to delay all transfer switch and engine-starting signals.

  • Transfer to emergency time delay. Adjustable from 0 to 5 minutes for controlled timing of load transfer to emergency.

  • Retransfer to normal time delay. Adjustable to 30 minutes.

  • Five-minute unloaded running time delay for emergency engine generator cool down.

  • Four-second time delay to override momentary to ignore momentary voltage and frequency transients during initial GenSet loading.


  • Adjustable three-phase, close differential voltage sensing on normal source.

  • Normal source pickup voltage is adjustable to 95% of nominal; drop-out is adjustable from 70 to 90% of nominal.

  • Frequency sensing on emergency source. Pickup at 95% and dropout at 85% of nominal.


  • Switch position indicating contacts (rated 10 amps 250VAC, 32VDC). (1) for Normal position, (1) for Emergency position.

  • Gold plated engine start contacts (rated 5 amps 28VDC or 120VAC).


  • Remote test switch.

  • Remote contact for test or for peak shaving applications. Circuit will be automatically bypassed if emergency source fails.

  • Inhibit transfer to emergency.

  • Remote time delay bypass switch.

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