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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
switch. In regard to periodic operation, check the
matic switch-operating mechanisms at the switch
manufacturer's instructions to ensure that the
location.
switch hasn't frozen closed. The following general
b. Insulation. Insulation for the voltage and cur-
rules apply:
rent interrupting level may be provided by operat-
a. All switches. The following applies to the oper-
ing the contacts in air, oil, vacuum, or in a sulfur
hexifluoride (SF,) gas medium.
ating of all switches:
c. Load interrupting ability. Switches are classi-
(1) Check visually that the blade is fully closed
fied by their ability to interrupt load.
and latched or fully open, as intended by the opera-
(1) Disconnecting switch. This is a device used
tion.
to open, close, or change the connections in a circuit
(2) The operating mechanism is designed prop-
or system. It has no interrupting rating and is used
erly for the switch and use of undue force, in the
for isolating equipment only after the circuit has
nature of an extension of the operating handle, or
been opened by some other means. Two special
an extra person on the operating handle or switch
types are as follows:
stick, may cause severe damage to the switch or
(a) Grounding switch. This is a switch used
operating mechanism. Freeing of an iced switch
to connect a circuit or piece of equipment to ground.
mechanism may be assisted by a few sharp raps on
(b) Horn-gap switch. This is a switch pro-
the vertical operating pipe or suddenly applied tugs
vided with arcing horns to aid in dispersing any arc
on the operating handle.
that may occur when the switch is operated. This
(3) Operate power-operated switches periodi-
combination is sometimes referred to as an air-
cally to ensure that their mechanisms and control
break switch. It should not be operated except to
features are functioning properly. If the circuit can-
interrupt the charging current of a short length of
not be de-energized to operate a switch, the operat-
line, or the magnetizing current of a de-energized
ing mechanism should be disengaged from the link-
transformer. Oil switches should always be consid-
age. Check control circuits and mechanisms in the
ered as disconnect switches, unless the switch
disengaged manner, unless disengagement will
nameplate indicates a fault-closing rating suitable
change the overall adjustment.
for the system's maximum available fault.
b. Disconnecting switches:
(2) Interru p ter switches. Interrupter switches
(1) Check that no load is being carried by the
have specific capabilities for switching one or more
switch, prior to operating a disconnecting or horn-
of the following type of loads: 0.8 minimum lagging
gap switch.
power factor load, parallel or loop load, transformer
(2) Check to determine that operation does not
magnetizing load, line charging load, cable charging
remove necessary safety grounds, prior to opening a
load, and capacitor bank load. Follow the manufac-
grounding switch. Check the circuit to confirm that
turer's instructions when operating interrupter
it is not energized, prior to closing.
switches.
(3) Operate disconnecting switches rapidly to
(a) Nonfault closing type. This is a switch
reduce arcing time and possible burning of contacts.
equipped with means of interrupting current, at
rated voltage, not in excess of the switch's continu-
8-11. Switch maintenance.
ous rated current. Interrupter switches, which do
No work should be done on switches until both sides
not have a fault-closing rating, may be damaged if
of each phase are de-energized and properly
inadvertently closed on a short circuit. Appropriate
grounded. In addition to the recommendations
precautions should be taken to avoid danger to the
given herein, follow the specific maintenance direc-
operator.
tions of the switch manufacturer. For insulating
(b) Fault closing type. This is a switch
medium other than air, treat as described in Section
equipped with means for interrupting current, at
IV.
rated voltage, in excess of the switch's continuous
a. Frequency of inspection. Switches should be
rated current. Interrupter switches with fault-
inspected visually at a frequency determined by lo-
closing ratings are intended to provide adequate
cal conditions such as atmospheric contamination,
personnel protection, when closing into a short cir-
use of contamination control coatings, frequency of
cuit, up to the asymmetrical fault-closing rating of
operation, or fault current exposure.
the switch and when applied in accordance with the
manufacturer's recommendation.
(1) Need. If a switch cannot be maintained on a
periodic basis, its service life may be affected. When
8-10. Operation of Switches.
operated, it is recommended that the switch be
opened and closed several times in order to clean
Appropriate safety rules should be followed with
special regard to the interrupti ng rating of the
the contacts and free the moving parts.
8-4
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