a lightning strike can lift both Ph & N above earth - you did not say whether there was one on the Ph too (?)
Thanks, but no, its only from neutral to earth.
As far as i can see, its only lighting strikes that this GDT could be useful against? (assuming it had the suitable current limiting element in there)
Gas discharge tubes without additional current limiting elements are not suitable for AC power line surge protection.
Thanks. There is only a 12R series resistor and its in the live line for current limiting. What sort of current limiter were you indicating may i ask? The common mode choke woudl also provide impedance as you know, though i suspect even being a CM choke, it would likely saturate at these current levels.
Also, i presume that the GDT would likely fail open, and so adding this GDT, even without a current limiter, wouldnt do any harm?...just perhaps a waste of money.
Why is is not common to see GDT proection to earth on offline SMPS's?
Also, as you know, a 500V AC test is often done from live and neutral connections to earth in production.,.......so a 470V GDT would surely break over during this.....so why do people use 470V ones?