The connection of SPDs using CT1 appears to provide protection only in common mode. That seems be the normal method employed. However, looking at CT2 am I correct in assuming that the clamp voltage would need to be very much less as the protection is provided across the conductors supplying load components? It seems to me that CT1 is for lightning and CT2 more for overvoltages derived from switching???
a guarded yes, 
For CT2, neither line is ever more than Vclamp from PE at the point of surge protection, and at worst L may be going up by 1kV while N is going down so then the L-N difference is indeed 2* Vclamp, - though just as often they could both see a jump in same polarity so the LN difference may be small even if both arrestors are clipping relative to PE
But of course as you move along the cables and away from the surge protector towards the origin of the over-voltage, then voltage slopes due to Mr. Ohms law and even more confusingly the effects of V= L*di/dt grab you in a rather rate-of-rise time dependent way.
And V clamp is only that 1kV single figure at the crest of a current pulse with very particular test waveform, it is not a level at which a flat-top is always guaranteed.
Mike.
Could you tell if this is CT1 or CT2? According to Hager it is CT2.
Could you tell if this is CT1 or CT2? According to Hager it is CT2.
