TEST INSTRUMENT SAFETY
WARNING
Normal useof testequipmentexposesyouto a certainamount of dangerfrom electricalshock
becausetesting must often be performed where exposedvoltage is present. An electrical shock
causing 10miliamps of currentto passthrough theheartwill stopmosthumanheartbeats.Voltage
aslow as35volts dc or ac rmsshouldbeconsidereddangerousandhazardoussinceit canproduce
alethal current undercertainconditions. Highervoltagesposeanevengreaterthreatbecausesuch
voltage canmore easilyproducea lethalcurrent. Your normal work habitisshould include all ac-
cepted practices that will preventcontact with exposedhigh voltage. and that will steercurrent
away from your heart is caseof accidental contact with a high voltage. You will significantly
reduce the risk factor is you know and observethe following safetyprecautions:
Don't exposehigh voltage needlessly.Removehousingsand covers only whennecessary.
Turn off equipment while making testconnectionsin high-voltagecircuits. Dischargehigh-
voltage capacitors after removing power.
2.
Usean insulated floor material or a large,insulated floor mat to stand on, and aninsulated
work surface on which to placeequipment; and makecertain-suchsurfacesare not damp or
wet. Whereinsulated floor surfaceis not available, wear heavygloves.
3. Use the time-proven "one hand in the pocket" technique while handling an instrument
probe. Be particularly careful to avoid contacting a nearbymetal object thatcould providea
good ground return path.
Always use an isolation transformer to power transformerless "hot chassis" equipment,
whereone sideof the ac powerline isconnecteddirectly to thechassis.This includesmostre-
cent television setsand audio equipment. Without an isolation transformer, the chassisof
suchequipment maybe floating at line voltage (120VAC, 60 Hz in USA), dependingupon
which way the2-wireac power plugis inserted. Not only doesthis presentadangerousshock
hazard if the chassisis touched, but damageto test instrumentsor the equipmentunder test
may result from connectingtheground lead of sometestinstrumentsto a "hot" chassis.The
ground lead of this function generatorand most other test instruments with 3-wire power
plugs is at earthground.
S. On testinstruments or any equipmentwith a 3-wireac power plug, useonly a 3-wireoutlet.
This isa safety feature to keepthe housing or other exposedelementsat earthground.
6. If possible,familiarize yourself with the equipmentbeingtestedand the location of its high
votage points. However, rememberthat high voltage may appear at unexpectedpoints in
defectiveequipment.
7.
Also rememberthat acline voltage ispresentonsomepower input current points suchason.
off switches,fuses,power transformers, etc., evenwhen the equipmentis turned off.
8. Never work alone. Someoneshould be nearbyto renderaid if necessary.Training on CPR
(cardo-pulmonary resuscitation)first aid is highly recommended.
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