ASCO Transfer Switch Overview

Healthcare Applications

In healthcare settings, ASCO Transfer Switches are vital for maintaining uninterrupted power to life-support systems and critical medical equipment.

Diagram Description: A city scene illustrating a healthcare facility connected to Critical Power Management Systems, Load Banks, Transfer Switches, and Power Control Systems, demonstrating integrated power solutions.

Applications for Critical Power Equipment

ASCO provides solutions for a wide range of applications:

• Data Center

  Ensuring Maximum Uptime for critical IT infrastructure.

  Diagram Description: An interior view of a modern data center with rows of servers, highlighting the integration of Transfer Switches.

• Commercial Building

  Maintaining Business Continuity through reliable power.

  Diagram Description: A cross-section of a multi-story commercial building, showing Transfer Switches integrated into its power distribution for continuous operation.

• Residential Healthcare Facilities

  Providing Occupant Safety & Comfort.

  Diagram Description: An exterior view of a residential healthcare facility with a transfer switch unit and integrated quick-connect ports.

• Small Business/Critical Operations

  Ensuring Public Service continuity.

  Diagram Description: An exterior view of a small business or critical operation site (e.g., gas station) with a transfer switch and integrated quick-connect ports.

• Telecom

  Guaranteeing Public Safety & Consumer Satisfaction.

  Diagram Description: An outdoor telecom equipment site with a transfer switch unit.

• Water Treatment Plant

  Ensuring Environmental Protection.

  Diagram Description: An aerial view of a water treatment plant with visible transfer switch installations.

How Transfer Switches Work

Transfer switches are installed in power distribution systems to connect electrical loads to different power sources. They safely switch loads between two isolated sources, such as utility power and an emergency generator.

Diagram Description: A simplified electrical schematic showing two power sources, "Utility" and "Emergency Genset", connected through an "ATS" (Automatic Transfer Switch) to a "Load". A "Service Entrance" is also indicated.

Automatic transfer switches provide essential functions without human intervention:

• Carry rated current continuously.
• Detect power failure on the primary source.
• Start the alternate power source.
• Transfer the load.
• Sense restoration of power to the primary source.
• Re-transfer the load to the primary source.

Image Description: A 4-Pole Transfer Switching Mechanism.

Automatic Transfer Switch Components

• Enclosure

  Available in a range of UL-rated types, rugged enclosures protect equipment and ensure reliability in various indoor and outdoor environments.

• Transfer Mechanism

  Electrically operated and mechanically held, solenoid-powered mechanisms reliably transfer load quickly for demanding applications.

• Communications and Metering

  Features range from simple indicators to remote annunciators, enabling real-time monitoring, control, and integration with building automation systems.

• Controller

  An electronic controller stores operating criteria, senses electrical conditions, executes transfer sequences, and stores operational data.

Listings and Ratings

✔️ Every ASCO Transfer Switch is listed to UL 1008 – Standard for Safety - Transfer Switch Equipment. UL 1008 testing ensures high overload and fault current endurance for thousands of switching cycles, guaranteeing safety, reliability, and longevity.

ASCO Transfer Switches offer Withstand and Closing Ratings indicating the current they can withstand under short circuit conditions. Time-Based Ratings support selective coordination of fault-clearing devices.

Transfer Switch Models by Type of Operation

• Automatic

  Automatically switch loads to emergency power and back without human intervention.

• Non-Automatic

  Require operator-initiated, local, or remote electrical controls to transfer loads on command.

• Manual

  The simplest type, requiring manual operation of a mechanical switching mechanism.

Images Description: Examples of Automatic, Non-Automatic, and Manual transfer switch units.

Standard Transfer Switch

Reliably transfers electrical load between sources of power.

Diagram Description: Electrical schematic for a Standard Transfer Switch showing Utility and Emergency sources connected via ATS to Load.

Bypass-Isolation Transfer Switch

Features concurrent maintainability; the bypass feature enables isolation of the transfer mechanism for service and repair.

Diagram Description: Electrical schematic for a Bypass-Isolation Transfer Switch, illustrating Utility, Emergency, ATS, Bypass path, and Load.

Service Entrance Transfer Switch

Simplifies design, procurement, and installation by incorporating the service disconnect within the transfer switch enclosure or lineup.

Diagram Description: Electrical schematic for a Service Entrance Transfer Switch, including Utility, Emergency, ATS, Overcurrent Protection, and Load.

Neutral Configurations

Transfer switches differ by neutral configurations:

• Solid Neutral

  Standard configuration for power distribution systems with a single grounding electrode.

  Diagram Description: Electrical schematic illustrating a Solid Neutral configuration, showing ATS and Load with a single neutral connection.

• Switched Neutral

  Used for transferring load between separately grounded systems.

  Diagram Description: Electrical schematic illustrating a Switched Neutral configuration, showing ATS and Load with a switched neutral connection.

• Overlapping Neutral

  Used for transferring load between separately derived systems without interrupting neutral connectivity.

  Diagram Description: Electrical schematic illustrating an Overlapping Neutral configuration, showing ATS and Load with an overlapping neutral connection.

"With nine hospitals on the line, ASCO helps me sleep well at night.”

– Tom M., Facility Engineering Director

Transition Modes by Transfer Sequence

• Open Transition

  Operation: "Break-Before-Make". Popular for resistive & mixed loads. Used across a wide range of facilities & industries. Standard In-Phase Transfer Capability.

  Diagram Description: Graph showing Voltage vs. Time for Open Transition, with a distinct break in power before the connection is made. Load Current pulse of ~40mS.

• Delayed Transition

  Operation: "Break-Wait-Make". Suitable for inductive & motor load applications. Allows residual voltages of motors & inductive devices to decay prior to avoiding damaging transient currents.

  Diagram Description: Graph showing Voltage vs. Time for Delayed Transition, with a significant pause (break-wait) before the connection is made. Load Current shown over seconds to minutes.

• Closed Transition

  Operation: "Make-Before-Break" transfers without momentary power interruption. Reduces electrical disturbance to downstream loads when transferring between two live sources. Ideal for mission-critical operations, healthcare facilities, & data centers.

  Diagram Description: Graph showing Voltage vs. Time for Closed Transition, with a brief overlap where both sources are momentarily connected. Load Current pulse of <100mS.

Custom Engineered Transfer Switch and Distribution

"Value-Added Transfer Switches": Custom switches increase value by integrating service, distribution, and control features in custom-engineered designs.

Customization Options:

• Integrated Distribution Breakers
• Source Fusing
• Bus Riser

Custom-Engineered Transfer Switches can offer:

• Reduced Space Requirements
• Reduced Lead and Construction Times
• Reduced Installation Labor
• Enhanced Quality Control

Diagram Description: Simplified electrical schematic for a custom engineered transfer switch system showing Utility and Emergency sources connected via ATS to Load 1 and Load 2, with Disconnect Signal Circuit and Pilot Contact.

Series Overview

• 7000 SERIES

  Custom engineered for healthcare, data center, and mission-critical facilities. Industry-leading technology for the widest range of applications.

  Applications: Hospitals, Data Centers, Mission Critical Facilities.

  Image Description: ASCO 7000 Series transfer switch unit.

• 4000 SERIES

  Sophisticated control for large commercial and industrial loads. Features premium options in a configured-to-order solution.

  Applications: Large Commercial Applications, Large Industrial Facilities, Water Treatment Plants.

  Image Description: ASCO 4000 Series transfer switch unit.

• SERIES 300

  Standard designs for commercial and light industrial facilities. Simple to procure, install, and commission.

  Applications: Outpatient Healthcare Facilities, Small & Midsize Businesses, Light Industrial Applications, Integrated & Stand-Alone Quick Connects.

  Image Description: ASCO Series 300 transfer switch unit.

• SERIES 185

  Economical designs for homes and small businesses.

  Applications: Small Businesses, Residential Applications.

  Image Description: ASCO Series 185 transfer switch unit.

Product Series Comparison

Resource Finder

Find additional resources for each product series:

• Product Web Page: 7000 Series (Low Voltage Web Page, Medium Voltage Web Page), 4000 Series (Web Page), 300 Series (Web Page), 185 Series (Web Page)
• Product Brochure: 7000 Series (Low Voltage Pub.3040, Medium Voltage Pub.2060), 4000 Series (Pub.3144), 300 Series (Pub.1195), 185 Series (Pub.3214)
• Available Ratings: View Supporting Documentation
• White Papers: View Transfer Switch Papers
• Technical Articles: View Transfer Switch Articles
• Videos: View Transfer Switch Videos