Preferred FlexFit 110 - Electrical Noise Suppression; General Wiring Requirements

2-12 Installation – Electrical Noise Suppression
FlexFit – Linkageless Control – Revision 1.0
PREFERRED
UTILITIES MFG CORPORATION
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Electrical Noise Suppression
In addition to safety code requirements, there are numerous methods and practices that help to reduce nuisance start-up and
operational problems due to electrical noise. Variable Speed Drives (VSDs) and ignition transformers are the major electrical noise
generators on a boiler system, and their installation should be closely scrutinized.
General Wiring Requirements
Physically separate AC wiring from DC wiring. Do not run AC and DC wiring in the same conduit or trough. When necessary,
AC and DC wiring should cross at a 90-degree angle.
DC shielded cables: The drain/shield should be connected at one end only, and only as shown on the electrical drawings that
follow. Generally, the shield is connected to the DC common of its power supply (not to earth ground). All shield foils and shield wires
should be insulated (taped or heat shrink) to prevent accidental connection to earth or power ground. Shields connected at both ends,
or unintentional second grounds, can add extra noise to a signal instead of reducing noise.
Ignition Transformer Wiring / Mounting
Ignition transformers should be mounted as close to the spark electrode as possible to keep the igniter lead wire short and to
make the return current path through the burner steel to the transformer as short as possible. Igniter spark gaps should be as small
as possible but within the burner manufacturing recommendation.
Ensure there is good grounding contact of the transformer end of the igniter assembly (use star washers).
Use only automotive style resistance core ignition wire. Do not use copper core ignition wire.
VSD Wiring
The wiring from the VSD output to the motor must be in a dedicated conduit and must be separate from all other wirings. Do
not run the VSD input wiring in this conduit. Do not run through junction boxes that include any other wiring.
VSD outputs generate high levels of electrical noise. The metal conduit and conduit connectors contain the noise inside the
conduit. The VSD to motor conduit must be metallic and have either threaded or non-insulating compression ttings. PVC conduit
and EMT set screw-style hub connectors are not acceptable.
A dedicated ground wire must be run from the VSD frame to the motor frame within the motor conduit for safety and to reduce
electrical noise. A second ground wire must be run from the VSD frame to the AC power source for NEC safety grounding.
All DC wiring conduits should be kept as far away from VSD-to-motor conduits as possible.
Preferred Utilities strongly recommends that the wiring between the VSD and the motor be of a shielded cable specically
designed for suppression of the electrical noise associated with the VSD (available from Alpha Wire or Belden).
Oxygen Analyzer Wiring
Use only P/N 190130 cable for O
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detector wiring. Run this cable in a separate conduit from the detector back to the control
panel. Avoid splices. Only a shielded thermocouple wire used for ue gas temperature can be run with the O
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cable. No other wires,
AC or DC, are allowed in this conduit. To assure that the integrity of system communications is maintained and that the adverse
inuence of electrical noise is minimized, it is required that the BMU-CABLE-XX for interconnection of the FlexFit between the LCD
and Servos and Catalog Number 190130 ZP O2 Analyzer to FlexFit interconnecting cable is used in the interconnection of these
devices. Preferred Utilities will not warranty the operation of the FlexFit system if wired in any other form.
Maximum wiring length is 500 feet.
Connect the detector ground wire directly to the FlexFit power supply ground.
Do not connect any shield drain wires at the detector. Insulate shields to prevent shorts to ground or to other shields.
Connect the O
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cable shield drain wires to the (S) terminals as shown on the drawings.
Flame Scanner Wiring
If a Preferred Instruments ame scanner with the included cable is used, the connecting eld wiring must be installed exactly
as shown. The wire shield is connected to earth ground at the scanner via the prefabricated cable and must be insulated at all other
locations to prevent accidental grounding. Do not connect the shield wire to the FlexFit terminals.
For all other scanners, the FlexFit requires a 120 VAC input on terminal FR for the ame scanner signal.
For all other scanners where the ame intensity inputs will be utilized, contact Preferred Instruments Technical Support for the
proper wiring requirements.