To prevent unintentional interference during testing and servicing, intrinsically safe circuits must be identified at terminal and junction locations [504.80]. Obviously, there’s a problem if you can’t read the labels.
Tag every cable and terminal with clear, legible, and durable labels. Doing this is part of good workmanship [110.12]. It also reduces confusion, prevents errors, and reduces downtime.
A professional-level label tool makes the labeling task much easier, and you may find the advanced models worth the additional investment. A good labeler pays for itself in short order.
If you don’t have a labeler but do have a squeaky-tight budget, look for other ways to cut expenses. For example, you don’t have to seal enclosures that contain only intrinsically safe apparatus, except as required by 501.15(F)(3)) [504.70].