Using Transistor And Triac Output Modules - Hitachi HSC-2100 Hardware Manual

(2) Service life of relay contacts
If these relays are intended to be operated at rated voltage and rated current, their expected
service life is approximately 100,000 switching operations (1,800 cycles per hour).
However, if the relays are operated at a higher voltage and a higher current level than the
rated, their useful service life will be shorter than expected. The other factors that will
make the service life shorter than expected are the following: ambient operating
environment, type of the load connected, in-rush current, and serge. So, pay special
attention to those factors when installing any of the above-mentioned hardware modules.
As a rule, each of those factors should be checked before using the hardware module to
which a load is actually connected, or the hardware module should be replaced regularly
before its service life is over. It is recommended that, where a long service life is required
of a hardware module, the hardware module should be a transistor output module or triac
output module, not a hardware module containing a relay for output.

5.1.3 Using transistor and triac output modules

Transistor output modules and triac output modules may have their output device break down or
burn if a large current flows in their output circuit in the event of a shorted load, cable miswiring,
the accidental contact of wires, or other causes.
To avoid this, observe the following rule. When you connect a load to a transistor or triac output
module, be sure to wire fuses between the load and the output terminals, as shown below. These
fuses must be fast acting ones each of whose rated current is 2 or more times larger than the rated
current of the load. However, you should note that, even if such fuses are installed in the circuit,
the output device may be damaged due to a short circuit at the load, depending on the nature of
the short circuit. For this reason, preventive maintenance should be carried out on the output
module to eliminate any possibility of a short circuit. For example, check the cable and wiring
periodically for any exposed part of a conductor, any damage to the cable, and so forth.
(a) Wiring fuses for the models
LWO600 and LWO650
Output module
(c) Wiring fuses for the model LWO670
Output module
Fuse
Load
Fuse
L
- +
Fuse
12 to 24 VDC
Fuse Load
L
100 VAC Fuse
5 MAKING USE OF MODULES
(b) Wiring fuses for the model
LWO610
Output module
5-3
Fuse 12 to 24 VDC
+ -
L
Fuse Load