Situation is the following. You are requested to assemble and install:
1) plug and socket together with cable
2) a cable reel
for to use in possible hazardous environment.
Is it a manufacturing? Who ever does it becomes a manufacturer according to relevant Ex / Hazloc regulations? both YES.
So both have become a product under Ex. It means there is a need for a manufacturer and all docs accordingly (Ex certificate, manual, DoC, label, etc). Needs to be designed, installed, inspected, operated, maintained and repaired as per Ex.
Keep up good work!