RWB II ROTARY SCREW COMPRESSOR UNITS
PROPER INSTALLATION OF ELECTRONIC EQUIPMENT
S70-210 IOM
Page 43
PROPER INSTALLATION OF ELECTRONIC EQUIPMENT
IN AN INDUSTRIAL ENVIRONMENT
In today’s refrigeration plants, electronic controls have found
their way into almost every aspect of refrigeration control.
Electronic controls have brought to the industry more precise
control, improved energy savings and operator conveniences.
Electronic control devices have revolutionized the way refrig-
eration plants operate today.
The earlier relay systems were virtually immune to radio
frequency interference (RFI), electromagnetic interference
(EMI), and ground loop currents. Therefore installation and
wiring were of little consequence and the wiring job con-
sisted of hooking up the point-to-point wiring and sizing the
wire properly. In an electronic system, improper installation
will cause problems that outweigh the benefits of electronic
control. Electronic equipment is susceptible to RFI, EMI, and
ground loop currents which can cause equipment shutdowns,
processor memory and program loss, erratic behavior,
and false readings. Manufacturers of industrial electronic
equipment take into consideration the effects of RFI, EMI,
and ground loop currents and incorporate protection of the
electronics in their designs. These manufacturers require
that certain installation precautions be taken to protect the
electronics from these effects. All electronic equipment must
be viewed as sensitive instrumentation and therefore requires
careful attention to installation procedures. These procedures
are well known to instrument engineers, but are usually not
followed by general electricians.
There are a few basics, that if followed, will result in a trou-
ble-free installation. The National Electric Code (NEC) is a
guideline for safe wiring practices, but it does not deal with
procedures used for electronic control installation. Use the
following procedures for electronic equipment installa-
tion. These procedures do not override any rules by the NEC,
but are to be used in conjunction with the NEC code.
WIRE SIZING
Size supply wires one size larger than required for
amperage draw to reduce instantaneous voltage dips
caused by large loads such as heaters and contactors
and solenoids. These sudden dips in voltage can cause the
processor, whether it be a microprocessor, a computer, or a
PLC to malfunction momentarily or cause a complete reset
of the control system. If the wire is loaded to its maximum
capacity, the voltage dips are much larger, and the potential
of a malfunction is very high. If the wire is sized one size
larger than required, the voltage dips are smaller than in a
fully loaded supply wire, and the potential for malfunction
is much lower. The NEC code book calls for specific wire
sizes to be used based on current draw. An example of this
would be to use #14 gauge wire for circuits up to 15 amp or
#12 gauge wire for circuits of up to 20 amp. Therefore, when
connecting the power feed circuit to an electronic industrial
control, use #12 gauge wire for a maximum current draw
of 15 amp and #10 wire for a maximum current draw of 20
amp. Use this rule of thumb to minimize voltage dips at the
electronic control.
VOLTAGE SOURCE
Selecting the voltage source is extremely important for proper
operation of electronic equipment in an industrial environ-
ment. Standard procedure for electronic instrumentation
is to provide a “clean” separate source voltage in order to
prevent EMI, from other equipment in the plant, from inter-
fering with the operation of the electronic equipment. Con-
necting electronic equipment to a breaker panel (also known
as lighting panels and fuse panels) subjects the electronic
equipment to noise generated by other devices connected
to the breaker panel. This noise is known as electromagnetic
interference (EMI). EMI flows on the wires that are common
to a circuit. EMI cannot travel easily through transformers
and therefore can be isolated from selected circuits. Use
a control transformer to isolate the electronic control
panel from other equipment in the plant that generate
EMI. (Figure 39)
Figure 39
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