UL Standard for Safety Transfer Switch Equipment
|Publication Date:||22 December 2014|
This standard applies to the following types of transfer switches that have a maximum rating of 1000 volts for use in non-hazardous locations, in accordance with Annex A1, Item 1:
a) Automatic transfer switches;
b) Manual or non-automatic transfer switches;
c) Closed transition transfer switches;
d) Hybrid transfer switches;
e) Transfer switches for fire pumps;
f) Bypass/isolating switches;
g) Softload transfer switches;
h) Transfer switches intended for use as service equipment;
i) Transfer switches intended for use in mobile/portable applications such as recreational vehicles, motor homes, camping trailers, and mobile health care facilities; and
j) In Mexico and the United States, branch circuit emergency lighting transfer switches (BCELTS). In Canada, the requirements for BCELTS do not apply.
This standard specifically does not apply to:
a) Double-throw switches for use in optional standby systems;
b) Switches used in equipment manufactured in accordance with Annex A1, Item 9;
c) In Canada, manually operated generator transfer panels in accordance with Annex A1, Item 12.
d) Transfer switches rated over 1000 V;
e) Solid-state (static) transfer equipment;
f) Transfer switches for aircraft; and
g) Transfer switches for water craft.
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. In Mexico and the United States, this requirement does not apply.
These requirements cover enclosed inlets intended to facilitate connection of portable generators to transfer equipment.