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Site Considerations for Equipment Installation, Grounding, and Wiring Manual
D301452X012
October 2019
Provide external strain relief (using tie wrap, etc.) to prevent the loss of slack at the controller/flow
computer.
Be careful to use wire that is appropriately sized for the load. Refer to the equipment
manufacturer's specifications and the National Electrical Code Handbook for information on wire
size and wire resistance. After installing the field wiring, test each load to determine if the correct
voltage or current is present at the load. If you know the resistance of the field wires (Circular Mills x
Length) you should be able to calculate the load voltage. Conversely, if you know the minimum
load voltage and current, you should be able to derive the maximum voltage loss that is allowable
due to line resistance and then the correct wire size.
Referring to
total line resistance of 20 ohms, the load voltage (voltage across the relay) should be:
Figure 5-3. Calculating Load Voltage due to Line Resistance
Note
In the figure above, V
multiplied by the current through them.
5.2.9
Use Lightning Arresters & Surge Protectors
Use lightning arresters in association with any radio or modem equipped unit. Some modems are
equipped with surge protection circuitry. Place lightning arresters or antenna discharge units on
the base of the antenna and at the point where the antenna lead (typically coaxial cable) enters the
site equipment building. When a modem is used, place a lightning arrester at the point where the
phone line enters the site equipment building. If you use a modem that does not include surge
protection circuitry, you should also install a surge suppressors or lightning arrester on the phone
line as close to the modem as possible. Any unit interfaced to a radio or modem must be connected to
a known good earth ground.
5.2.10
Secure Wiring Connections
Make sure that all wiring connections are secure. Over time, wires that were once round become
flattened due to the pressure applied by screw compression type terminals and site vibrations.
After a while these compression screws can become loose. Part of a good maintenance routine
should be to check and tighten all screws associated with wiring terminal connections. Avoid
30
Figure
5-3, a relay that is picked by 100 mA, with a loop supply voltage of 24V and a
VL = VS - (VC + VC) where VC + VC = (RC + RC) I
22 = 24 - 2
is the loss in the conductor. It is equal to the resistance of the conductors
c
where 2V
= (20 Ω ) x 0.1 A
Wiring Techniques
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