Advertisement
TYPES OF LOAD
■ Resistance load
Resistance load is a power factor of 1 (cos φ = 1) where the load
is only for the resistance portion. The displayed switch rating
indicates the current capacity when using AC current.
■ DC load
Differing from AC, since the direction of current is fixed for DC,
the continuous arc time lengthens when the same voltage is
applied.
■ Incandescent lamp load
Since an inrush current of 10 to 15 times the rated current flows
for an instant when the switch is turned on for the lamp,
adhesion of the contacts may occur. Therefore, please take into
consideration this transient current when selecting a switch.
■ Induction load
Since arc generation due to reverse voltage can cause contact
failure to occur when there is an induction load (in relays,
solenoids and buzzers, etc.), we recommend you insert a
suitable spark quenching circuit (see figure below).
Circuit example
Switch contact
r
c
R
Switch contact
r
R
c
Switch contact
diode
R
Switch contact
ZNR
Varistor
Notes
(1) r = more than 10 Ω
(2) In an AC circuit,
impedance of R is to be slightly smaller
than impedance of r and c.
Can be used for both AC and DC circuits.
r = R
C: 0.1 μF
For DC circuits only.
Can be used for both AC and DC circuits.
Technical Terminology & Cautions for Use
■ Motor load
Contacts may adhere due to the starting current at the start of
motor operation which is three to eight times the steady-state
current. Although it differs depending on the motor, since a
current flows that is several times that of the nominal current,
please select a switch taking into consideration the values in the
table below. To make the motor rotate in reverse, use an ON-
OFF-ON switch and take measures to prevent a multiplier
current (starting current + reverse current) from flowing.
Motor type
Three-phase
Squirrel-cage
induction motor
Split-phase-start
Single-phase
Capacitor-start
induction motor
Repulsion-start
A current that is approximately two times that of the starting
current will flow when reverse rotation is caused during
operation. Also, when using for a load that will cause transient
phenomena such as when operating the motor in reverse
rotation or switching the poles, an arc short (circuit short) may
occur due to the time lag between poles when switching. Please
be careful.
Example of 1-pole motor reverse rotation circuit
M
Good wiring
Example of single-phase induction motor
(capacitor) strong-weak switching circuit
Strong
M
Weak
Strong
Weak
Good wiring
Example of three-phase motor
M
Good wiring
■ Capacitor load
In the case of mercury lamps, florescent lamps and the
capacitor loads of capacitor circuits, since an extremely large
inrush current flows when the switch is turned on, please
measure that transient value with the actual load and then either
use the product keeping within the range of the rated current or
after verifying the actual load.
–7–
Type
Starting current
Approx. 5 to 8 times current listed on
nameplate
Approx. 6 times current listed on
nameplate
Approx. 4 to 5 times current listed on
nameplate
Approx. 3 times current listed on
nameplate
M
Power
supply
Power
supply
Bad wiring
Strong
M
Weak
Strong
Power
supply
Bad wiring
reverse rotation circuit
M
Power
supply
Power
supply
Bad wiring
AECTB38E 201811-T
Advertisement
