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Wire Gauge

W A T L O W

The size or gauge of wire should beselected by calculating the maximum circuit current and choosing thegauge fulfilling that requirement. Using sizes a great deal larger than required will generally increase the likelihood of electrostatic (capaci-tance) coupling of noise. Ground Loops In an optimized system, ground loopswould be eliminated in the entire control system. There are obvious loops which can be spotted by studying the “as-built” wiring diagram.There are also the not-so-obvious ground loops that result from the technique of connecting internal circuits common in the manufacturer’sequipment. An example would be if a control circuit is designed to work diode with the proper voltage ratingfor the circuit wired in reverse across the coil to suppress backemf.•A“MOV” (Metal Oxide Varistor) canbe installed across the ac line tolimit voltage “spikes” that occur onthe ac supply lines as a result of lightning strikes, switching large motors, etc. The MOV is available in several varieties for 115 or 220V Å (ac) lines. The MOVdissipates the voltage “spikes” to ground. However, MOVs have alimited life, because repeatedaction deteriorates the device.•An Islatrol

Application Guide catalog - 7347 Application Guide

Wiring Practices

Earth Ground
Wiring Practices

Helpful Wiring Guidelines

Ensure optimum controllerperformance by having a good earth ground. Some controllers havespecific grounding requirements.Refer to the specific controller manuals for terminal connectioninstructions. Continuedwith a grounded sensor input. By ob-taining an internal schematic for the control equipment, identifying howcommon connections are done, andtransferring that information to the “as-built” wiring diagram, one can easily determine if ground loops are created. Ground Each Chassis Ground the chassis of each piece ofequipment in the system. Connect each individual chassis to the overallequipment chassis immediatelyadjacent to that piece and tie all major chassis ground terminals toge- ther with one lead (usually green wire)to ground at one single point. No Daisy Chains Chassis Grounds vs. Commons For best noise immunity, avoid daisychaining ac power (or return) lines or output signal (or return) lines to multiple control circuits. Use direct, individual pairs of lines from thepower source to each devicerequiring ac power. Avoid paralleling L1 (power lead) and L2 (return lead)to load power solenoids, contactors and control circuits. If L1 (power lead) is used to switch a load, the L2 line(return lead) will have the same switched voltage potential and couldcouple unwanted noise into a control circuit. Do not confuse chassis grounds(safety ground) with control circuitcommons or with ac supply lines L2 (return or neutral line). Each returnsystem wiring must be kept separate.Make sure the chassis ground (safety)is never used as a conductor to returncircuit current. Get lt at the Source Other techniques to prevent prob-lems include eliminating the noise at, or as close to the source as possible. These include the following:•A Quencharc
® usemedia (electromagnetic filtering), other than electric circuits to filterout electrical noise. Care must betaken in matching the powercapabilities of the filter with thepower demands of the circuit.•The ultimate protection is an “un-interruptable power supply” (UPS). This device senses the ac powerline, and when it fluctuates, a bat-tery powered 60Hz inverted circuit takes over supplying power withinone-half to one cycle of the ac line.
® may be placedacross the terminals of devicessuch as relays, relay contacts, solenoids, motors, etc., to filter out noise generated by such devices. A Quencharc Å (ac), non-polar capacitor inseries with a 100 ohm,
® is a simple RC sup-pression device using a 0.1µf 600V
1 �
2 wattresistor. This device can be used on ac or dc circuits to effectively dampen noise at its source. Any dc relay solenoids, etc., should have a
® , and other similarpower line filters are designed to carry the power for the control circuit and at the same time bufferthe control circuit from ac line noise. Devices like an Islatrol
Quencharc ® is a registered trademark of ITW Pakton.Islatrol ® is a registered trademark of Control Concepts Corporation. 119