You will be required to work on energized equipment during many of your job assignments. For example, as you troubleshoot a piece of electronic equipment, the technical manual may instruct you to measure voltages or to check signal waveforms while the equipment is energized. If so, before you connect the multimeter or the oscilloscope, there are certain safety precautions and procedures you MUST follow that are designed to protect you from electric shock. These precautions and procedures are divided into two

Table 3-2.-Procedures to Follow When Measuring Voltages Below 300 Volts

basic voltage categories: (1) voltage measurements below 300 volts, and (2) voltage measurements above 300 volts.

VOLTAGES BELOW 300 VOLTS

Most of the voltage measurements that you will make will be below 300 volts. Almost all the newer electronic systems operate at less than 28 volts, except for the main input ac power. Table 3-2 lists the safety procedures for measuring voltages below 300 volts. Follow them!

In addition to the procedures in table 3-2, you must obey the four safety precautions in table 3-4 when you take measurements on energized equipment.

The following excerpt from a mishap report shows the importance of following these precautions:

Table 3-3.-Rubber Glove Ratings

"A technician could not get the alligator clip on the test lead to stay on the probe, so he held the clip to the probe with his right hand. He violated safety precautions by continuing to hold the clip and the probe while he was energizing the test lead with 1,200 volts. Soon

Table 3-4.-Safety Precautions For Measuring Voltages Below 300 Volts

thereafter, he touched the ground lead and received a serious shock. He was treated for minor burns on the palm."

VOLTAGES ABOVE 300 VOLTS

All the safety procedures for measuring voltages below 300 volts also apply when you are measuring voltages above 300 volts. However, the big difference when measuring voltages above 300 volts is that you must NOT hold the test probe while the equipment is energized. Instead, you must attach the test probes while the equipment is de-energized. (Refer to table 3-5).