Ampacity is short for ampere capacity. For welding cables, ampacity refers to the maximum amount of electrical current a spool of cable can conduct before advanced deterioration sets in.
For more detail on ampacity, see welding cable ampacity.
AC and DC are just descriptions of how electric charges move in a live circuit. Like any conductor, a welding cable can carry both AC and DC power.
Whether you are using an AC or DC welder matters more for determining what kind of electrode to use and affects what kind of weld you get.
As long as the welding cable can handle the number of amps being generated at a given voltage (not exceeding 600 volts), it will work.
Welding machines will generate either AC or DC power, but both AC and DC are just descriptions of how electric charges move in a live circuit.
The type of power your welding machine uses matters more for determining what kind of electrode to use than what kind of welding cable.
Welding machines that generate DC power are more common because of the ability to control the polarity (charge) of the electrode, which affects the kind of weld you get. In relation to welding cables.
If your welding machine does not have a switch to change polarity then you will need to change the cable terminals.
With DC Electrode Positive (DCEP, DC+), also known as DC Reverse Polarity (DCRP), the heat from the arc is greater at the electrode as electrons flow from the work piece to the electrode.
With DC Electrode Negative or (DCEN, DC-), also known as DC Straight Polarity (DCSP), the heat from the arc is greater at the workpiece as electrons flow from the electrode to the metal.
Always go with what the manufacturer says concerning the use of an electrode since there are different electrodes designed for DCEP and DCEN.
AC welding machines require special AC electrodes since there is no fixed polarity.
However, when using AC electrodes on DC machines there is typically one polarity with which the electrode works best.