UL 1008 Transfer Switch Equipment

The UL 1008 Transfer Switch Equipment standard, developed by Underwriter Laboratories (UL), describes the requirements for the following types of transfer switches, defined in the standard appendix (Appendix A1), designed for use in non-hazardous areas and with a maximum voltage of 1000 Volts:

• Automatic transfer switches
• Manual or non-automatic transfer switches
• Closed transition transfer switches
• Hybrid transfer switches
• Transfer switches for fire pumps
• Bypass / isolating switches
• Soft load transfer switches
• Transfer switches designed for use as service equipment
• Transfer switches designed for use in mobile/portable applications such as recreational vehicles, RVs, camping trailers and mobile healthcare facilities
• Input assemblies for transfer switch equipment
• Arc resistant transfer switch equipment
• Hardwired transfer switch equipment
• Combination meter/transfer equipment assemblies
• Branch circuit emergency lighting transfer switches in Mexico and the USA (this requirement does not apply in Canada)

The following equipment is outside the scope of this standard:

• Double-throw switches for use in optional standby systems
• Switches used in equipment manufactured in accordance with the annex of this standard (Annex A1)
• In Canada, manually operated generator transfer panels in accordance with Annex A1
• Transfer switches rated over 1000 Volts
• Solid state (static) transfer equipment
• Transfer switches for aircraft
• Transfer switches for watercraft

The requirements described in the UL 1008 standard apply to the following types of devices:

• Transfer switches and their associated control devices, including voltage sensing relays, frequency sensing relays, time delay relays, and the like
• Open types designed for installation in other equipment such as totally enclosed transfer switches and switchgear panels
• Bypass/isolation switches used to manually select an available power source to feed load circuits and provide complete isolation of the automatic transfer switch (these switches may be totally enclosed, enclosed with the transfer switch, or open type designed to be mounted on other equipment)

Automatic transfer switches constructed to the optional standby requirements of this standard are not permitted in Canada. Additionally, this requirement does not apply in Mexico and the United States.

These requirements also include closed inlets designed to facilitate the connection of portable generators to transfer equipment.

Meanwhile, the UL 1008 standard includes annexes with requirements covering the following equipment:

• Bypass / isolation switches
• Transfer switches for fire pump service
• Hybrid transfer switches
• Soft load transfer switches
• Instrumentation and calibration of high capacity circuits
• Sample markings
• Input assemblies for transfer switch equipment
• Arc resistant transfer switch equipment
• Electromagnetic compatibility (EMC) requirements for transfer switches
• Hardwired transfer switch equipment
• Combination meter/transfer equipment assemblies

Transfer switches are devices that allow different electrical sources to be safely connected or disconnected to an electrical load. Many residences and businesses are equipped with a standby generator that is used in the event of a power outage. Many university campuses and factories also have their own on-site power plants, but occasionally switch to the local grid for power. Some industrial users have sophisticated electrical systems with multiple on-site generators and grid access points that can be connected to different electrical loads. In all cases, it is important to properly isolate electrical generation sources when they are not in use and to ensure that transitions from one source to another occur in a safe and controlled manner.

In general, transfer switches are required for three categories of use cases:

• Transfer switches between the utility service and the generator
• Between different generators
• To switch between different network service entries

Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, it also provides testing services defined in the "UL 1008 Transfer switch equipment" standard with its trained and expert staff and advanced technological equipment.