arpadveress 
The meaning, often ignored, of “U” and “X” characters inside the certificate, represents one of the problems that frequently cause disagreements through the chain from the manufacturer of junction boxes, to the inspector, passing across the technician. Those are not simple topics to understand and, for this reason, we invite you to study very well the relevant points of the standard which treat them.
In conclusion, let me remind You that “U” and “X” symbols must not be present at the same time on the same plate, because the previous one indicates a component and the second one a device.
Keep up good work!
Arpad
exprofessional.com
