[Amps] Air Gap

[Dennis Berry]

Still learning about high power amps, so please excuse this simple question.  A reply about air gap recently said:

>> Bill -- What is the length of air gap that is arcing?
>
> About 1/8" between plates.

  Tnx, Bill.     0.125" has a working potential rating of 4500v, which 
is at least 1200v higher that what should be there.
end


Is the air gap measured from the stator to stator plates, or between the rotor to stator plate?  My assumption is that it is between the rotor to stator plate as that would be the minimum spacing?

The ARRL handbook references the air puncture voltage is 240 volts per 0.001 inch.  But that doesn't work out for the 0.125" referenced in the above question.

Thanks in advance for replies,

Dennis