What the 1N6279-E3/73 actually does on a board
The peak pulse current of 47 A (10/1000 µs) tells you the clamp can sink that surge current without converting the transient into thermal damage, provided the event is brief and infrequent.
Three voltage specs that drive the protection design
The reverse standoff voltage of 17.8 V is the DC working voltage the line sits behind in normal operation — the TVS stays reverse-biased and essentially invisible at that level. Power Line Protection is listed as No — this part is designed for signal-line and secondary protection on non-mains-power circuits, not for direct AC line entry protection.
Thermal margin and package
The DO-201AA (also called DO-27) axial body mounts through-hole with the cathode band marking the standard polarity convention — band towards the protected node in a reverse-bias orientation.