Usually the 30A means absolute max of 30 amps of current. This is typically a function of the size of the internal switch contacts and the process if how they mate. The max voltage is part of the equation also. I personally would divide the amps number by two and just plan for 15 maybe 20 amps of current going through the contacts.
The 125v is 125 volts and refers to the maximum voltage that is intended to be on the contacts when they engage at the specified current rating. In the first example the manufacturer doesnt intend for more than 125volts with 30 amps of current to be waiting on the contacts when they close.
