The data I have is from technical presentation they provide to their dealers. It goes though much more depth than their web site.
Just briefly on your question, I don't have data on what surge caused those specific failures. But the general fault mode is clear: an MOV creates a short once its avalanche voltage is hit. Once there, it starts to cook. So two failures can occur:
1. The MOV is undersized. This causes overheat and smoke. I am told UL certification requires testing for one leg at at time. So if the surge is concurrent, then overall heat dissipation becomes too high resulting in charred circuits. TPS devices are rates for all circuits shorting out this way.
2. The surge is beyond what its rating is. This is what you want the fuse for.
The key thing here is that should any failure occur, this company will fix the device for free. Because of that, they are much more inclined to make sure it is a sound design than not.
Also, they have a superb local rep which has been exceptionally helpful with information and follow through for us. As an example, we had a very high-end customer who had frequent power failures and resulting equipment losses. They asked us to come and expand their current system (we had not done the original work) and we put in the TPS and a big rack worth of gear. Using the belts and suspenders style of work
, the crew also put line of use devices in the rack consisting of APC UPS and Furman surge protection devices. Customer calls back and says that anytime the power fails and generator kicks in, all the gear goes down. We go and investigate. As soon as the generator would kick, the APC would go in battery mode and not come out even after the generator took over. And the Furman would fault and trip its breaker (or something like it -- I did not go there personally).
Feeling safe that we had whole house protection, we thought this was just a glitch with line of use devices and suggestion was made to simply remove them all. But not being a fan of blind fixes, I asked that we properly troubleshoot why this was occurring. So we asked TPS rep company to prove to us their box was indeed clipping the surge voltage as it should have. They sent out a specialist with measurement gear to analyze the problem. What a shocker. He found out the transfer switch for the generator was wired wrong and it was dumping 120 volts into neutral (or something like it -- again I was not there personally) and our gear was being subjected to double the normal line voltage!!! Mind you, this is not a small system. The generator has a 10 cylinder engine that is the size of a double car garage! Clearly whoever did the electrical work had no clue what they were doing and the poor customer was suffering for years this way. Since our company technicians are also licensed electricians we went it and rewired the transfer switch and all is well now.
So good learning here: even though whole house system obviates the need for line of use surge protection, their *fault detection* logic still proved useful. Without that, we would have pushed this high voltage surge into our gear and would have had no end of weird failures to deal with in the future.
Anyway, suggest contacting the local rep if you are in the market. When it comes to professionally installed gear like this, you want the right one put in there or why bother