The installer should adhere to the minimum bending radiuses when routing wire from the roof line to ground level or to the ground rods. When wire is bent at sharp angles, the wire stretches on the curve, creating a smaller diameter with higher resistance at that point. If the energy level from a lightning strike is large enough it will discharge to the adjacent metal when it reaches that point of higher resistance.
Buildings with fiberglass or other nonmetallic material on the roof and sides are typically supported by steel, so metal strapping or electrical wire should bond all pieces of steel, as per NFPA 780 standards.
Sewer lift stations and water booster pump stations typically have a radio for transmitting data back to a central location. Stream-delaying air terminals should be installed on the top of all poles or towers used for the radio antenna. The lightning rod should be higher than the antenna and be installed in a manner that does not place it in the path of radio waves.
A lightning rod installed on a pole or tower to protect a radio antenna provides a zone of protection that extends outward and down at a 45-degree angle from the top of the lightning rod. If there is a building adjacent to the antenna pole that is completely within that zone of protection, it is not necessary to install air terminals on the building.SURGE SUPPRESSORS
A complete lightning protection system requires the installation of transient voltage surge suppressors (TVSS) on all AC and DC electrical circuits. That will provide protection from the effects of lightning-induced currents, substation switching transients, and internally generated transients resulting from inductive or capacitive load switching.
McRory & Williams suggests the installation of TVSS:
- Between the step-down transformer and the three-phase distribution panel for the remote telemetry unit (RTU) used for the SCADA panel.
- On all 4- to 20-milliamp analog inputs to, as well as outputs from, the RTU panel.
- On the antenna cable located between the antenna and the radio for the SCADA system.
- On the 120 VAC power and the 24 VDC power to the field-mounted transmitters.
- On any field-mounted breaker, variable-frequency drive, programmable logic controller, or any other instrument in a location where it's likely to be struck by lightning.
- On all LAN lines, telephone lines, digital data lines, and computer highway cables.
- On the 120 V power lines to all computers, remote telemetry units, radios, or programmable logic controllers.
This standard addresses the installation of surge suppressors on all levels of AC voltage at or below 277/480 V AC and DC voltage at or below 35 V. Surge suppressors are typically wired in parallel with AC voltage devices and in series with devices that operate on low-voltage DC.
When installing TVSS in buildings with older equipment, don't assume markings and nameplates on cabinets are true indications of what is inside. It is likely that years of revisions and ongoing improvements necessary for continued operations have resulted in modifications to the cabinets.
The MAWSS standard directs the contractor on new projects to visit each existing site. At each site, the contractor should remove the face of the motor control cabinets, panels, and other equipment; determine the exact type of connections, number of phases, Delta versus Y arrangement, voltage level, and number of wires to be hooked up before ordering any equipment; and specify the actual surge suppressor to be purchased for each site and service. The contractor is also responsible for the surge suppressor's compatibility with existing equipment.
Radio antennas for SCADA systems at remote locations are oftentimes the high point at the site. A surge suppressor should be installed in the cabling between the antenna and the radio. The suppressor should be installed in a NEMA 4X box outside the building. There should also be a solid copper wire installed between the surge suppressors and the ground system for the site.