What happens when a fuse blows or a breaker fails its maintenance inspection? You replace it with one just like it, right? But how do you know the existing overcurrent protection device (OCPD) is correct in the first place?

Will the replacement device correctly handle the fault current available at that point in the electrical system? You can’t possibly know the correct answer unless you can refer to a short circuit study. That short circuit study must be up-to-date with any changes made since the original installation.

Will the replacement OCPD trip at the right time? You can’t possibly know the correct answer without a selective coordination study. The wrong answer can mean burned up equipment or needless loss of production.

You don’t have time to conduct either study while production is down and operators are nervously awaiting an OCPD replacement. The solution is to schedule (and perform) the studies, determine the correct OCPDs and part numbers, and then update the OCPD replacement information. Then, you can be confident the replacement OCPDs are the correct ones.

This doesn’t mean you should wait for incorrect OCPDs to fail before replacing them. That either defeats the purpose of having OCPDs in the first place or puts production at risk of nuisance trips. After conducting the studies, review the existing OCPDs against the new specifications and systematically correct any differences.