Copyright Goodheart-Willcox Co., Inc. 184 Essential Electrical Skills for HVACR: Theory and Labs Test leads eventually fail. They must be checked with the resistance function by using alligator clips to connect leads together. While observing the display, hold one probe and move the wire in a circular motion at the strain relief area. See Figure 10-19. The displayed value should remain constant. Repeat this test for each connection. A flickering display reveals a break in the wire. Visually inspect lead insulation for cracks and damage. Make sure test lead plugs securely connect to meter jacks. Probe tip shields are used to reduce the amount of exposed metal, Figure 10-20. This is to reduce arc flash risk. If the metal probes are in close proximity, current can arc across them due to a high potential difference. Insulated alligator clips allow the technician to leave a meter connected while evaluating other parts of the system. Goodheart-Willcox Publisher Figure 10-19. Check leads by connecting probes together and moving wire in circular motion while observing display. A break in the lead wire is indicated by flashing random numbers displayed. Probe tip shields Finger guard Long reach tips Alligator clips Goodheart-Willcox Publisher Figure 10-20. Various test lead probe attachments.