Det-Tronics EA2100CG Eagle 2000 Communication Gateway - Manual (Page 21)

Moisture can have a detrimental effect on the perfor-
mance of electronic devices. Therefore, it is important
to take proper precautions during installation to ensure
that moisture will not come in contact with the electrical
connections or components of the system.
In installations that do not use wiring conduit, the use of
properly installed watertight glands is required to pre-
vent the entry of moisture into the device enclosure.
In applications where the wiring cable is installed in
conduit, the conduit must not be used for wiring to other
electrical equipment. In addition, the use of conduit
seals is required to prevent damage to electrical con-
nections caused by condensation within the conduit.
Conduit seals must be watertight and explosion-proof
and are to be installed even if they are not required by
local wiring codes. A seal must be located as close to
the enclosure as possible. In no case should this seal
be located more than 18 inches (46 cm) from the
device.
When pouring a seal, the use of a fiber dam is required
to assure proper formation of the seal. Seals should
never be poured in temperatures that are below freez-
ing, since the water in the sealing compound will freeze
and the compound will not dry properly. Contamination
problems can result when temperatures rise above the
freezing point and the compound thaws.
The shielding of the cable should be stripped back to
permit the seal to form around the individual leads,
rather than around the outside of the shield. This will
prevent any siphoning action that can occur through the
inside of the shield.
It is recommended that conduit breathers also be used.
In some applications, alternate changes in temperature
and barometric pressure can cause “breathing,” which
allows the entry and circulation of moist air throughout
the conduit. Joints in the conduit system and its com-
ponents are seldom tight enough to prevent this
“breathing.” Moisture in the air can condense at the
base of vertical conduit runs and equipment enclosures,
and can build up over a period of time. This can be
detrimental to electronic devices. To eliminate this con-
dition, explosion-proof drains and breathers should be
installed to automatically bleed off accumulated water.
Always observe the requirements of local codes.
NOTE
Any deviation from the recommended wiring prac-
tices can compromise system operation. Consult
the factory if different wiring types or methods are
being considered.
NOTE
Many Eagle system electronic modules contain semi-
conductor devices that are susceptible to damage by
electrostatic discharge. An electrostatic charge can
build up on the skin and discharge when an object is
touched. Therefore, use caution when handling, tak-
ing care not to touch the terminals or electronic com-
ponents. For more information on proper handling,
refer to Service Memo form 75-1005.
DETERMINING GAUGE OF POWER
WIRING
To ensure proper operation of the devices on the com-
munication loop, it is important to consider the size of
the power wiring. Since the resistance of the wiring will
cause a drop in voltage across the wiring, the operating
voltage at the input of the devices on the loop will be
lower than the voltage at the output of the power supply.
If the total resistance of the wiring is too great, the oper-
ating voltage will be too low for the device to operate
properly. The following list of variables must be consid-
ered when selecting the power wiring:
Wire size. For any given length of wire, the total resis-
tance is determined by the gauge of the wire. Table 5
shows the resistance of various wire gauges for each
1000 feet of copper wire.
Wiring length. The total resistance of a length of wire
increases in direct proportion to the length of the wire.
NOTE: SHIELDS GROUNDED AT GATEWAY ONLY.
SHIELDS CONNECTED TO EACH OTHER (NOT TO GROUND)
AT EACH NODE BUT OPEN AT ONE NODE NEAR MIDDLE OF LOOP.
B1611
NODE NODE NODE
NODE NODE GATEWAY
17 95-8424
Figure 15—Recommended Grounding for Cable Shields
Table 5—Typical Resistance for Stranded Copper Wire at 75˚C
Wire Size Ohms per 1,000 Feet
(AWG) at 75 ˚ C
18 7.765
16 4.884
14 3.071
12 1.931
10 1.215
8 0.764