pitting caused by arcing or corrosion. If pitting is present, smooth the contacts with a fine file or number
00 sandpaper. Be certain the contacts make proper contact when the operating mechanism is ON.
Check the connections at the terminals to be certain the terminals and wiring are tight and free from
corrosion. Check all mounting hardware for tightness and wear. Check all components for wear. Clean the
circuit breaker completely.
When you have finished working on the circuit breaker, restore power and remove the tag from the
switch that applies power to the circuit.
Q42. What steps are to be taken before beginning work on a circuit breaker?
Q43. What items are you to check when working on a circuit breaker?
This chapter has provided the information to enable you to have a basic understanding of circuit
protection devices. The following is a summary of the main points in this chapter.
CIRCUIT PROTECTION DEVICES are needed to protect personnel and circuits from hazardous
conditions. The hazardous conditions can be caused by a direct short, excessive current, or excessive heat.
Circuit protection devices are always connected in series with the circuit being protected.
A DIRECT SHORT is a condition in which some point in the circuit, where full system voltage is
present, comes in direct contact with the ground or return side of the circuit.
EXCESSIVE CURRENT describes a condition that is not a direct short but in which circuit current
increases beyond the designed current carrying ability of the circuit.
EXCESSIVE HEAT describes a condition in which the heat in or around a circuit increases to a
higher than normal level.
FUSES and CIRCUIT BREAKERS are the two types of circuit protection devices discussed in this