Understanding UL and Breaker Interlock Kits
To help understand UL (Underwriting Laboratory) standards we need to start with a little history. In the early 1900’s, as electricity started to be used in homes and factories, it became obvious there were significant risks of fire from these new electrical products. Insurance companies (underwriters) needed a way to limit their risks. Several insurance companies decided to fund a study of what was needed, and this study led to the formation of a company (UL) that would write standards for devices including electrical devices. By ensuring their customers only used devices that met these standards, the insurance companies significantly reduced their lability. The next step was then obvious, someone needed to test each new product to see that it met or exceeded these standards thus the formation of the testing division. While they worked together, they were really two different operations, setting the standards and testing to those standards. Many years later, the federal government under OSHA certified UL as the keeper of the standards but allowed other qualified testing laboratories such as MET Labs and Wyle Labs to test to these standards.
About the same time, it was obvious there needed to be standards for what devices were required for electrical installations and how they were installed. This led to the writing of the NEC (National Electrical Code). The NEC would tell you what you needed and how to install it and UL would set the standards for the devices and materials and the labs would make sure that they met the standards. Then the AHJ (Authority Having Jurisdiction or electrical inspector) would make sure that each project had the required approved equipment, and the installation met the NEC requirements.
Section 702 of the NEC requires a mechanical interlock between two power sources to prevent the interconnection of the two sources. In the case of using a standby generator you never want to cross connect the utility and the generator and you certainly never want to push power back on a utility line that could injure or kill a lineman who is working to restore power. Remember, transformers work both ways and your 240 volts from your generator turns in 10,000+ volts on the utility poles!
UL 67 covers panelboards and what are commonly known as breaker panels. While there is no specific standard for mechanical interlocks, the testing laboratories test to ensure that the installed interlock kit does prevent more than one power source from being on at a time and that “as an accessory to the panel” it does not alter the UL listing for the panel that it is mounted on.
Generator Interlock Technologies was the founder of retrofit interlock devices over 20 years. Today, just like our first day, we continue to pride ourselves on selling a top-of-the-line interlock kit line. Manufacturing takes place in Richmond, Virginia, where kits are laser cut from heavy gauge stainless steel. Today Kits are tested twice annually in Cary, North Carolina, at Met Laboratories to UL 67 standards!