220.127.116.11 Potential Differences. Voltage detectors are used to determine whether
the line or device is energized. Low-voltage detectors often use neon glow lamps or
solenoid plunger testers. Glow lamps are not recommended as they can pick up stray
induced voltages and give a false indication that the line is energized. Medium- and high-
voltage detectors are proximity and direct-contact types. Direct-contact type detectors
may not be effective on circuits not connected to ground, and proximity-type detectors
may not be effective where magnetic fields can cancel (such as cable potheads).
Proximity-type detectors cannot detect nonalternating (dc) voltages. Never use portable
multimeters for measurements on medium- and high-voltage systems. Always check a
voltage detector for proper operation using the "hot-dead-hot" method: first, check the
detector on a known energized circuit, then check the desired line or device for voltage,
and last, check the detector on a known energized circuit.
18.104.22.168 Phasing Testers. Phasing testers are used to determine the phase
relationship of energized lines. Short circuits occur when different phases are tied
together. A phasing tester can use two high-resistance units on hot sticks connected by a
phasing-out voltmeter. Where voltage transformers are available, a voltmeter can be
connected between one side to the other side. If lines are in phase, the voltmeter will
register zero. If performing a phasing check at a generator disconnect, the maximum
voltage rating of the phasing tester should be at least two times the nominal rated voltage
of the circuit to be tested.
22.214.171.124 Combustible Gas/Oxygen Detectors. Portable monitors provide visual
and audible warnings of explosive atmospheres and/or low oxygen levels that often occur
in confined spaces. A continuous reading is given of any gas concentration ranging from 0
to 100 percent of the lower explosive limit (LEL) and 0 to 25 percent of the oxygen level.
A detector can be used to check battery rooms where ventilation is suspect. Determine if
a hazardous atmosphere exists before entering a confined space. Hazardous atmospheres
include: a contaminant concentration 10 percent or more of its lower explosive limit;
oxygen concentration less than 19.5 percent by volume; contaminant concentrations
exceeding specific OSHA standards (lead, asbestos, cadmium, and like substances); and
oxygen concentration more than 23 percent by volume, particularly if oil mist or other
combustible materials are present.
126.96.36.199 Aerial-Lift Bucket Truck Leakage-Current Monitoring. Leakage
current flows along the surface of tools or equipment due to the properties of the device's
surface and surface deposits. The permissible leakage current on aerial lifts is one
microampere per kilovolt ac or 0.5 microamperes per kilovolt dc. Adverse weather
conditions derate the normal dielectric quality of air that results in a greater leakage
current. Periodic testing is required. The use of a monitor on an aerial lift bucket truck
providing a continuous display of leakage current is recommended. The monitor should
sound an alarm at a pre-set leakage current level to alert workers to danger.
De-energized Line Work Prescheduling. De-energized line work
requires an electrical outage done in accordance with the facilities switching order
package. Table 16 lists the items that need to be developed for outage packages.