Let’s see, common mode transients are those occurring between lines and ground (LG and NG). Yes, neutral is a line, but if we don’t want to consider it a “line” then we have to differentiate two kinds of common mode transients, the ones between lines and ground (LG) and the ones occurring between neutral and ground (NG).
Normal mode transients are those occurring between each line and the others (LL and LN). Again, if we don’t want to consider the neutral as a line we should recognize two kinds of normal mode transients, the ones between lines, and the ones between lines an neutral.
At the system bonding jumper, neutral and ground became one, so in both cases (considering the neutral a line, or not doing so) the transients could appear between lines and this neutral-ground entity (LN = LG, common mode transients) or between lines (LL, normal mode transients). I don’t see why you insist in the non-existence of common mode transients.
By the way, normal mode transients may be called transverse mode transients or differential mode transients.
The paper you wrote, shows the difference between 7 and 4 devices TVSSs, both of them in common mode configuration. In your paper you show why when neutral and ground are bonded the use of a 7 device TVSS is equivalent to the use of a 4 device one. That could be theoretically correct, but that has nothing to do with normal mode versus common mode (or, if it does I don’t see it).
We have to remember that according to NEC 250.30 A 1, the system bonding jumper “ …shall be made at any single point on the separately derived system from the source to the first system disconnecting means or overcurrent device, ….”. So, there is no assurance that at the Class C TVSS the neutral-to-ground path is 0 ohms (or something equivalent) at the transient spectrum and considering the surge current capabilities. 300 amps only require an impedance of 1 ohm to produce 300 volts! I could agree with you in that for Class C TVSSs installed at service entrance the NG TVSS device could not be of much help in many applications; but I disagree with the idea of it being totally unnecessary in all kind of situations.
But all this is not too much critical at least we are thinking on individual TVSS devices (individual, 2 leads elements), because even those GE offers in the website you pointed at shown NG protection. I know, that protection is given by the series of TVSS devices between LN-LG, but anyway they are promoting it, so I’m afraid you need to keep working in your de-myth project, to make it really transparent (and not only concentrate in de-mystifying other manufacturers products while hiding your own myths [by the way, GE is not the only one doing this, most manufacturers may be doing the same]). So, if it is not possible to evade this NG protection, why bother arguing it is not necessary and it is a waste of time and money?
Please, this is not personal, I don’t want polemics, but as I stated before, we should be more careful with that solution-designing feeling that want to control us from time to time.
Joe.-
