West Control Solutions MRC 5000 Controller Manual - Manual (Page 8)

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2.3 PREPARATION FOR WIRING
Electrical noise interference is a phenomenon typical of industrial environments. Use the following guidelines which are
generally used to minimize the effect of electrical noise on instrumentation in general.
2.3.1 WIRING GUIDELINES
Listed below are some of the common sources of electrical noise in the industrial environment:
• Ignition Transformers
• Arc Welders
• Mechanical contact relay(s)
• Solenoids
Before using any instrument near the devices listed, the instructions below should be followed:
1. If the recorder is to be mounted in the same panel as any of the listed devices, separate them by the largest distance
possible.
2. If possible, replace electromechanical relay(s) with solid state relays.
3. Consider using a separate isolation transformer to power the recorder and any other instrumentation in the panel. The
transformer will serve to isolate the recorder from noise found on the AC power lines.
4. If the recorder is being installed on existing equipment, existing wiring should be inspected to insure that good wiring
practices have been followed.
5. Connect a good earth ground to the recorder chassis ground connection. To verify this, take a resistive measurement
from the instrument chassis to the nearest metal water pipe or proven earth ground. The reading should not exceed 100
ohms. Each instrument should have a dedicated earth ground. Do not chain link multiple instrument ground wires.
6. AC neutral should be at or near ground potential. To verify this, measure the AC voltage between neutral and ground.
The reading should be no more than 50 millivolts. If greater, the secondary of the transformer feeding the recorder should be
checked out by an electrician.
7. Wire Isolation/Segregation - this recorder is designed to promote proper separation of the wiring groups that connect to it.
The AC power terminals are located near the top of the instrument. The input signal terminals are located in the middle
section of the main board and the output alarm relay connections are on a separate board in the lower right hand corner of
the instrument.
8. Input Signal Wiring - Shielded cable helps eliminate electrical noise being induced on the wires. All input wires should be
run with shielded cable. Connection lead length should be kept as short as possible. The shield should be grounded at one
end only. The preferred grounding location is at the sensor, transmitter or transducer.
9. For severe levels of electrical noise, it may be necessary to suppress the noise at its source. Many manufacturers of
relays, contractors, etc. supply "surge suppressors" which mount on the noise source. For those devices that do not have
surge suppressors supplied, RC (resistance-capacitance) networks and/or MOVs (metal oxide varistors) may be added.
Inductive Loads - MOVs are recommended for transient suppression for inductive loads, and should be connected in parallel
and as close as possible to the load. See Figure 2-2. Additional protection may be provided by adding an RC network across
the load.
Contacts - Arcing may occur across contacts (relays or switches) when they open and close. This results in electrical noise
as well as damage to the contacts. Connecting an RC network, properly sized, in parallel, can eliminate this problem. See
Figure 2-3.
For circuits up to 3 amps, a combination of a 220 ohm resistor and 0.5 microfarad capacitor (1000 volts) is recommended.
For circuits from 3 to 5 amps, connect two of these in parallel. The resistor should be 1/4 watt or 1 watt for 115 VAC or
230VAC circuits, respectively.