I still have a PowerGuard on each of my railpower districts[photo below] but anymore they are basically just for observing the flashing voltage spike indicator lights. I have TVS installed at the secondary of the 180 PoHo transformers and downstream on the layout at Railpower Distribution T-strips in each power district.[operating TMCC and Conventional]. I am of an age that produces hand tremors so opening locomotives is no longer an option.
After dismantling a larger layout I donated one of of my surplus QSI PowerGuards to EE Dale Manquen for performing an autopsy of its voltage spike clamping capability versus Transient Voltage Suppressors. After his investigation Dale opined that the PowerGuards had comparatively insufficient voltage spike clamping capability---did not measure up to that of a simple inexpensive TVS.
Several years ago, I first learned of TVS from Bob Nelson, EE while posting on another Magazine's Forum. He was a big advocate of utilizing TVS on post war transformers , including the pw ZW. I was defending the purchase of my 5 QSI PowerGuards [$79 each] when he advised that I could accomplish effective voltage spike protection with the TVS and save about $78 per unit. It is difficult to argue based on ignorance so I eventually followed Nelson's advice regarding the use of TVS.
I cannot speak for EEs experienced in the characteristics of model railroad electronics such as Gunrunner John, Dale Manquen or Bob Nelson. But I have relied variously on their evaluation and comment regarding the nature of voltage spikes and overcurrent surges. Some opine that unlike an overcurrent surge, a voltage spike will not trip a breaker or blow a fuse. Thereby being one of the reasons for installing TVS to clamp the spike---the breaker/fuse doesn't interrupt it.
Also, unless you are using the 180 PoHo, with its very quick-acting electronic breaker, I believe fast blow fuses are better for reacting to control overcurrent surges than the typical 0-15 second trip time range of inexpensive thermal breakers such as the $4-5 Potter-Brumfield [which I used on two throttles of three pw ZWs for most of the 1990s]. Of course in my opinion the answer as regards external breaker use is purchase of more expensive magnetic units having rapid trip time.
My 2 cents.
