Anything involves in AC power has to be UL listed.
I don't think that's entirely true. A Nationally Recognized Testing Laboratory approval (UL, CSA, etc.) is generally not mandatory.
However, government entities won't buy unapproved equipment or devices, and most large businesses and wholesale and retail vendors will not buy or sell them. As a manufacturer of unapproved equipment, you may not be able to purchase product liability insurance without it.
As a consumer end user you may get an insurance fire claim refused if it can be proved that a unapproved device was responsible, depending on the insurance company and local jurisdiction.
Outside of some rare local jurisdictions that require it, a small manufacturer can produce and sell equipment without approval although you take a bigger risk with product liability and your potential market of resellers will be severely reduced.
Steve