UL certification requirements
As an example UL 1449 editions 3 and 4 cover industrial and residential surge suppression devices in the USA. Because of hazards they must be under UL and ISO regulations. In this case UL is about technical details and using UL approved parts such as X and Y rated capacitors for line to neutral and neutral to ground filtering. RoHS standards require lead-free solder.

ISO is more about documentation of both devices and the equipment used to test them. Then you have documentation about the documentation under a document control supervisor. It will drive you bonkers to implement this.

I would say to contact UL, FCC and ISO to find out if your product is under agency control of any kind. RF emitting devices have to follow FCC guidelines such that the container limits emissions to a stated level.

An exception would be DIY stuff not directly line connected and not emitting any radiation or RF noise or high voltage (shock hazard) or high current (burn hazard). But if you build and ship in large quantities it would behove you to analyse what the dangers are and any emissions and put a disclaimer on the product. Labels are a form of self-disclaimer such as "HIGH VOLTAGE", "SHOCK HAZARD" and "BURN HAZARD". This can fend off malpractice attorneys who would tear you to pieces if someone was injured by your product. By the way surge suppression devices must have all of the above labels and disclaimers about miss-use of product.

Before building anything for mass shipping I would get in touch with an attorney who can hire a pion to look into the myriad things that can bite you later on. You seriously need to get your ducks in a row before you ship anything that you or your employees built. Manufacturing can be an expensive business with lots of up-front cost, so consider the legal research worth it.