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Transfer Switch Equipment
standard by Underwriters Laboratories, 12/22/2014

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Please note: All interim revisions for this edition available at time of your purchase will be included.

This standard applies to:

  • Automatic transfer switches;
  • Manual or non-automatic transfer switches;
  • Closed transition transfer switches;
  • Hybrid transfer switches;
  • Transfer switches for fire pumps;
  • Bypass/isolating switches;
  • Softload transfer switches; and
  • Transfer switches intended for use as service equipment;

that have a maximum rating of 600 volts for use in non-hazardous locations, in accordance with Annex a1, Item 1.

This standard specifically does not apply to:

  • Double-throw switches for use in optional standby systems;
  • Switches used in equipment manufactured in accordance with Annex a1, Item 9;
  • In Canada, manually operated generator transfer panels in accordance with Annex a1, Item 12.
  • Transfer switches rated over 600 V; and
  • Solid-state (static) transfer equipment.

These requirements apply to transfer switches and their associated control devices including voltage sensing relays, frequency sensing relays, time-delay relays, and the like. These requirements apply to completely enclosed transfer switches and to open types intended for mounting in other equipment such as switchboards.

These requirements apply to bypass/isolation switches used to manually select an available power source to feed load circuits and to provide for total isolation of an automatic transfer switch. These switches may be completely enclosed, enclosed with the transfer switch, or of the open type intended for mounting in other equipment. Refer to Annex d. In Canada, automatic transfer switches built to the optional standby requirements of this standard are not permitted.

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