DCEN and DCEP were once known as “straight polarity” and “reverse polarity” respectively and those terms will be found in older reference books.

DCEN = DC Straight Polarity = DCSP

DCEP = DC Reverse Polarity = DCRP

Straight polarity, or “normal” polarity was used with the original bare and early light coated MMA electrodes.

Reverse polarity was achieved by “reversing the connections”.