Yardstick Service Life; Standard Tools And Measuring Instruments - Mitsubishi Electric C Series Handling And Maintenance

4.4 Yardstick service life

The maintenance and inspection shall be brought into practice depending on the environment where
the circuit-breaker is installed. The longevity of the circuit-breaker cannot be decided only in terms of
the year of use. Though the service life requires some diagnosis by some experts, the yardstick of
longevity may be as follows:
Yardstick for service life
Degree Environment
Places with ever clear and
1
dry air
Referential
use
Indoor where there is no
2 corrosive gas and little
conditions
dust
Places with little dust but
with such gases as salty,
1
sulfurous acid, hydrogen
Poor sulfide, high moisture
emvironment
Places with severe corro-
sive gases and dust where
2
humans cannot be for a
long time
The opening/closing life has been prescribed by IEC60947-2 as shown in the table above.
Note that the larger the frame of the circuit-breaker is, the more opening/closing life reduces.
Though the user might think these frequencies to be fewer than expected, this is because the circuit-
breaker is basically a protective device that differs from the switch intended for more frequent opening/
closing.
It is recommendable to install an electromagnetic contacter for opening/closing in a case where a
capacitor bank is switched in terms of the change in power factor.
Precaution should be taken in use of the circuit-breaker because the tripping by voltage tripping device,
in particular, reduces the service life.

4.5 Standard tools and measuring instruments

(1) Standard tools
Our circuit-breakers have been designed so that they may be installed and connected with commer-
cially available tools. Users are requested to mount and connect them using most appropriate tools.
Table below gives examples of tools ordinarily used.
Use
Screw tightening
Tightening of bolts and nuts
Note. Also commercially available are such tightening tools (torque wrench as generally called) that allow to control the tightening torque.
(2) Measuring instruments
Name
Multitester
This tester is used generally to measure the voltage in the maintenance and inspection work for circuit-breaker.
Thermistor thermometer
This enables an easy measurement of the temperature of terminals and molds.
Grip tester (clamp meter)
This makes it possible to measure the current of the electric part as electrified.
Measures the insulation resistance. A 500 VDC insulation resistance tester to be used in the maintenance and inspection of
Insulation resistance tester
circuit-breaker. (1000 VDC one not to be used)
Earth leakage breaker tester Measures the sensitivity current and operating time of the earth leakage breaker.
Replacement
Example
yardstick (year)
Dust-proof and air-condi-
About 10 to 20
tioned electrical room
Circuit-breakers in distribu-
tion boards and boxes in in-
About 7 to 15
dividual electrical rooms
without dust-proof and air-
conditioning
Geothermal power houses,
sewage treatment plants,
About 3 to 7
iron and steel works, paper
and pulp plants, etc.
Chemical plants, quarries,
About 1 to 3
mines, etc.
Name
Screwdrivers should be used whose diameters are of size suited to the diameters
of the cruciform grooves.
Size of diameter:
For M3, M4 and M5: No. 2
For M6 and M8: No. 3
Screwdriver
Double-ended wrench
The socket wrench allows to tighten rather firm. Pay your attention to it that it
may break too small bolts and/or buts or else any other bolts if the tightening
totque is too great.
Socket wrench
To be used for tightening hexagon socket cap screws.
Spanner with suitable diameter should be inserted into the bottom of the groove
and then turned.
Hexagonbar spanner
Size of circuit-
Number of operating cycles
breaker frame
Electrification No electrification
(A)
In ≤ 100
1500 8500
100 < In ≤ 315
1000 7000
315 < In ≤ 630
1000 4000
630 < In ≤ 2500
500 2500
2500 < In
500 1500
Remark: Number of operation by the test button of ELCB is 1000 times.
Remarks
Screwdriver shall be inserted into the
bottom of the groove and then turned.
Use
Number of operation by vol-
tage tripping, undervoltage
Total
tripping devices or trip button
10000
8000
10% of the total opening/
5000
closing frequency
3000
2000
78