A few basic rules for test equipment:

  • Clean and inspect test leads after each use. If you spot a problem, don't try to fix it. Replacing suspect test leads costs less than labor time spent on repair attempts, and repair attempts are seldom effective.
  • If someone steps on a test lead or rolls a cart over it, assume the insulation has been damaged. Replace the test lead.
  • Always apply test leads one at a time to terminals rather than applying two leads simultaneously, as this prevents arcing between the leads.
  • Know what environment you're measuring in. A DMM rated as CAT II isn't safe to use on a service panel.
Pop quiz: Do you know, without looking, the CAT rating of the DMM you use most often? Write down your answer. Now, check that DMM and see if you were correct. Where do you use this DMM?