If you are looking for some easy to read and understand info about TVSSs I suggest you to take a look at the following site:
http://www.surgex.com/library/42001.html For external transients suppression, panel mounted are the best option (Class “C” TVSS for ANSI/IEEE C62.41). There are many manufacturers available. I’ve used Liebert products in several occasions and they performed good (up to now). If pace of mind is important, you should provide both normal mode and common mode protection (LL, LN, LG, NG).
If you are concerned about budget (who’s not_?) you could (but I’m not recommending it) sacrifice LL protection because high external transients are more likely to be lighting induced common mode surges (all lines coming into the facility measured against ground). If the PoCo or another external facilities introduce in your panel high differential mode (surges between lines) transients, the LN, LG and NG sections of your TVSS together with a good grounding system will handle the job. If lightning is a concern you should check NFPA 780.
Hope this help,
Joe.-
