TEST INSTRUMENT SAFETY
WARNING
Normal use of test equipment exposes you to a certain amount of danger from electrical shock because testing
must often be performed where exposed high voltage is present. An electrical shock causing 10 milliamps of current
to pass through the heart will stop most human heartbeats. 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. Higher
voltage poses an even greater threat because such voltage can more easily produce a lethal current. 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 in the equipment under test. Remove housings and covers only when necessary. Turn
off equipment while making test connections in high-voltage circuits. Discharge high-voltage capacitors after removing
power.
2.
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.
3.
Use an insulated floor material or a large, insulated floor mat to stand on, and an insulated work surface on which to place
equipment; make certain such surfaces are not damp or wet.
4.
Use the time-proven “one hand in the 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.
5.
When using a probe, touch only the insulated portion. Never touch the exposed tip portion.
6.
When testing ac powered equipment, remember that ac line voltage is usually present on some power input circuits such as the
on-off switch, fuses, power transformer, etc. any time the equipment is connected to an ac outlet, even if the equipment is
turned off.
7.
Some equipment with a two-wire ac power cord, including some with polarized power plugs, is the “hot chassis” type. This
includes most recent television receivers and audio equipment. A plastic or wooden cabinet insulates the chassis to protect the
customer. When the cabinet is removed for servicing, a serious shock hazard exists if the chassis is touched. Not only does this
present a dangerous shock hazard, but damage to test instruments or the equipment under test may result from connecting the
ground lead of most test instruments (including this oscilloscope) to a “hot chassis”. To make measurements in “hot chassis”
equipment, always connect an isolation transformer between the ac outlet and the equipment under test. The
B&K Precision
Model TR-1 10 or 1604A Isolation Transformer, or Model 1653A or 1655A AC Power Supply is suitable for most applications.
To be on the safe side, treat all two wire ac powered equipment as “hot chassis” unless you are sure it has an isolated chassis or
an earth ground chassis.
8.
Never work alone. Someone should be nearby to render aid if necessary. Training in CPR (cardio-pulmonary resuscitation)
first aid is highly recommended
