Test Instrumrnt Safety

Electronic Test Instrument Safety Tips

Normal use of test equipment exposes you to a certain amount of danger from electrical shock because testing must often be performed where exposed voltage is present. An electrical shock causing 10 milliamps of current to pass through the heart will stop most human heartbeats. Higher voltages pose an even greater threat because such voltages can more easily produce a lethal current. However, voltage as low as 35 volts DC or AC RMS should be considered dangerous and hazardous since it can produce a lethal current under certain conditions. Your normal work habits should include all accepted practices that will prevent contact with exposed high voltage, and that will steer current away from your heart in case of accidental contact with a high voltage. You will significantly reduce the risk factor if you know and observe the following safety precautions:

 

 

 

1. Don't expose high voltage needlessly. Remove housings and covers only when necessary. Turn off equipment while making connections in high voltage circuits. Discharge high-voltage capacitors after removing power.

 

 

2. Use an insulated floor material or a large, insulated floor mat to stand on, and an isolated work surface on which to place equipment; and make certain such surfaces are not damp or wet. Where insulated floor surface is not available, wear heavy gloves.

 

 

3. Use the time-proven "one hand in the pocket" (preferably the left hand in pocket) technique while handling an instrument probe. Be particularly careful to avoid contacting a nearby metal object that could provide a good ground return path.

 

 

4. Always use an isolation transformer to power transformerless "hot chassis" equipment, where one side of the AC power line is connected directly to the chassis. This includes most recent television sets and audio equipment. Without an isolation transformer, the chassis of such equipment may be floating at line voltage (120 VAC, 60 Hz in the USA), depending upon which way the 2-wire AC power plug is inserted. Not only does this present a dangerous shock hazard if the chassis is touched, but damage to test instruments or the equipment under test may result from connecting the ground lead of some test instrument to a "hot" chassis. The ground lead of most oscilloscopes and most other test instruments with 3-wire power plugs is at earth ground. However, the GND jacks of this meter are isolated from earth ground.

 

 

5. On test instruments or any equipment with a 3-wire AC power plug, use only a 3-wire outlet.  This is a safety feature to keep the chassis and any other exposed elements at earth ground.

 

 

6. If possible, familiarize yourself with the equipment being tested and the location of its high voltage points. However, remember that high voltage may appear at unexpected points in defective equipment.

 

 

7. Also remember that AC line voltage is present on some power input circuit points such as on-off switches, fuses, power transformer, etc., even when the equipment is turned off.

 

 

8. When measuring high voltages we suggest   to avoid working alone as much as possible. Someone should be nearby to render   aid if necessary. Training in CPR (cardio-pulmonary resuscitation) first aid   is highly recommended.