First, UL says nothing about appliance protection. UL is about protecting humans. They do not care that a protector fails in testing. Only that a failure does not create a threat to human life. ie spit sparks or flame.
Second, 330 volts defines a protector for 120 volt service. It says nothing about protection. Only that a 200 volt protector and a 600 volt protector are not designed for 120 volt service.
A 600 volt protector does less protection for electronics because electronics have long been required to suffer up to 600 volt transients without damage. For 120 volt service, a 330 let-through voltage is required. Not higher. And not lower;.
Most electronics today have exceeded that "600 volt without damage" requirement. One Seasonic power supply defined its internal protection at 1,800 volts.
Ethernet was long required to suffer 2,000 volt transients without damage. This data interface chips (now obsolete) at
https://forums.hardwarezone.com.sg/threads/installing-a-whole-house-surge-protector.6688280/ , clearly states 15,000 volts without damage.
Electronics are some of THE most robust appliances in a house. A reality not found where fear creates conclusions. Electronics have become more robust (not more sensitive) over the decades. Specification numbers say so. Wild speculation, from so many others who ignore numbers, deny reality. To promote fear; not knowledge.
Third, 8/20 microsecond waveforms do not define a let-through voltage. Those define a protector part's joule rating. A different and unrelated parameter. UL 1449 says nothing about protection. It rates a protector to be a lesser threat to human life. Problem with UL 1449? This
still keeps happening.
Four, what determines how much spike reaches an appliance? Impedance and earth ground. UL does not test for nor discuss wire impedance nor earthing. Impedance (how a protector connects to earth ground) is a major factor in appliance protection. Impedance says nothing about human protection. So UL does not discuss it.
Some numbers. A plug-in protector tries to earth a tiny 100 amp surge down 50 feet of AC wire. That wire may be 0.3 ohms resistance. And 120 ohms impedance. 100 amps times 120 ohms is something less than 12,000 volts. Why less than? Because that spike must find other (destructive) paths to earth. Does same with a 330 volt protector or a 400 volt protector.
IEEE demonstrates this in a brochure. A protector in one room (without a low impedance - ie less than 10 foot - connection to earth) simply earthed that surge 8,000 volts destructively through a TV in an adjacent room. What difference would a 70 volt increased let-through voltage make? Nothing.
Why thousands of volts? Wire impedance. What paths are destructive and not destructive? UL says nothing. Since that is about appliance protection - not human protection.
A protector is only as effective as its connection to and quality of single point earth ground (all four words have electrical significance). Where does a let-through voltage have relevance? It doesn't. UL does not discuss that connect to earth ground nor the quality of earth ground electrodes. It is irrelevant to testing for human protection. And that is critical for making a protector effective.
Five, no protector does protection. Not one. A protector is only a connecting device to what does all protection. UL only tests the connecting device. UL says and tests nothing that actually defines and does protection. Protection of appliances is not the purpose of UL.
Six, being in a high rise means all such options are available and effective. Much of this research in the 1930s was done in the Empire State Building - also a high rise. A solution may be rented from the AC utility. First one of many options. However, if 'whole house' (Type 1 or Type 2) protectors are not properly earthed, then safest for both you and appliances is no Type 3 (plug-in) protector.
A protector, adjacent to electronics, can compromise (bypass) superior protection inside that appliance. As we engineers demonstrated in a design review. Where myths from observation were exposed and discounted.
Again, electronics (due to circuits required to power microprocessors) are among THE most robust appliance inside a house. For example, ethernet port must withstand up to 2,000 volts without damage. Another (now obsolete) interface chip defines protection up to 15,000 volts. (
https://datasheets.maximintegrated.com/en/ds/MAX1487E-MAX491E.pdf) We use well proven science reported by numbers in datasheets.
Seven, talk to anyone who experienced something. Most will only make conclusions from observations. All were taught, in elementary school science, that any conclusion only from observation is classic junk science.
We first learn why electronics failed (ie damage created by plug-in protectors). Sometimes fix things by tracing a surge path (replacing only semiconductors that conducted that surge). And even submitted some analysis to design reviews. A conclusions only from observation is junk science. Best evidence comes from the dead body - an autopsy.
We first discover a human mistake that made damage possible). And then use well proven science to correct that human mistake.
Eight, many protection systems do not even have protectors. Best protection on TV cable is a hardwire to single point earth ground. No protector required or installed to have best protection.
Numerous urban myths to unlearn. Starting with UL. UL says nothing about protecting appliances. UL says nothing about where a surge harmlessly dissipates. UL only tests items for threats to human life. A protector can fail - do no protection. And still can obtain a UL 1449 listing. Because it did not spit sparks or threaten human life during testing. Even when failed.