The author is national program manager for the Copper Development Association.
Lightning strikes and consequent power surges can seriously disrupt the operations of a radio station. Considering the tall structures and often remote locations of a radio broadcast station, lightning can and does strike more than once. Each time that it strikes, it can cause a station to go dark and cost thousands in repairs.
If the lightning protection of the radio station is inadequate in areas susceptible to thunderstorms, equipment damage and outages due to lightning strikes can occur on a frequent basis.
You might think nothing can be done about lightning strikes. They can be written off as bad luck or acts of God; and that may be true. However, a poorly-designed electrical system significantly contributes to the likelihood and magnitude of the problem and the extent of equipment damage.
A well-designed bonding and grounding system can greatly reduce the likelihood of damage, isolate the strike and reduce the costs for the majority of the lightning strikes.
It is possible to design lightning protection into a system using certain well-established best practices.
One of the leading experts on power quality and lightning protection is John West Sr. of Power & Systems Innovations of Tampa Inc. West is a well-known consultant with a reputation for rectifying electrical problems at broadcast, telecommunications and computer-based facilities. He has special expertise in the area of lightning strikes, not surprising for a consultant based in central Florida.
MARC RADIO GROUP
As an example of how a poorly designed electrical system can be reconfigured to reduce outages from lighting strikes, consider the case of the MARC Radio Group, headquartered in Gainesville (Fig. 1).
West was called in because of frequent lightning strikes that were costing thousands of dollars in electrical repairs and lost revenues. Something had to be done! Electrical outages caused by the lightning strikes were shutting down operations. Listeners were forced to change the channel and some did not tune in again. The group’s seven stations, including its consolidated studio operations, were suffering from outage after outage.
“When the storm season came to Florida, lightning hits would take out our stations’ equipment regularly,” said Frank Garcia, former chief information officer of the MARC Radio Group. “We would have outages almost every other week. We would have listeners tuning to other stations, and we’d have to work hard to get them back.”
West evaluated the situation and decided that electrical wiring, bonding and grounding problems at MARC Radio’s central building should be addressed first. The signals from this building carry the programming of the group’s AM and FM stations to the four remote transmitter sites that carry the respective programming.
The problems were prioritized and a plan was developed to fix them in stages. The main task was to properly re-bond all of the equipment to newly installed ground paths. Specific issues to be addressed were defined as follows:
- Avoiding mixed loads through a careful study of how the electrical power is distributed.
- Ensuring proper bonding connections of the electrical equipment.
- Establishing an adequate and reliable low-resistance grounding path.
- Proper grounding of the stand-by isolating power source.
These best practices translate into superior power quality as well as lightning protection. They are outlined here for consideration by all radio stations and not just those in lightning prone regions.
UNMIXED LOADS AND SPDS
Mixing loads is one of the biggest mistakes that can be made when installing circuits in a facility. At the central building, West found a panel containing feeds to the parking lot lights and elevator shared with other, sensitive equipment. That’s an invitation for disaster. The electrical wiring to the parking lot can conduct lightning currents back into the panel. The same panel also had circuits connecting to the main fire alarms, an air-conditioning compressor and the elevator loads.
According to West, such loads are highly inductive and should not be on the same panel as the fire alarms. “The alarms should have been isolated,” West said. “Combining these loads was done to save money but, in the long run, it will cost the end user much more. That’s poor economics.”
The remedy was to move the branches for the fire alarms and parking lot lights into separate panels. The air-conditioning and elevators were allowed to remain on a separate panel. A surge protection device (SPD) was installed on each panel. West recommends a surge protector be included on any panel that serves sensitive equipment. Originally, the surge protection was mounted two floors away from the main panel, essentially rendering it useless (Fig. 2).
Panel SPDs are installed on the feed end of the panel, as close as possible to the neutral bar so the lead length is kept short (Fig. 2). Properly installed, multiple SPDs can form layers of protection. The lowest resistance and impedance path to utility neutral and ground is the service entrance. That is where the most robust (highest kA rating) unit would be installed.
“My preference is to mount the first SPD ahead of the means of disconnect, that is, the main breaker. That is where the radio station owner should not hesitate to spend enough money to obtain a premium SPD. The further the wiring is into the building’s electrical system, the lower the kA rating of the SPD, but the rating should never drop below 40 to 50 kA,” West said.
“Each panel needs the surge protection to be correctly sized and properly connected. The SPD must be proximate to the circuit being protected. The farther away it is, the less effective it is,” he added. “The main power panel requires the most robust surge protector.”
West explains that surge protectors shunt excessive voltages to neutral or ground, or typically both. “You must use an appropriately sized conductor for that connection; otherwise, the effect is similar to flushing a toilet that has too small a drainpipe,” he said. In other words, using an undersized conductor dooms a surge protector to failure. West uses nothing less than 4/0 stranded copper.
“It should be understood that surge protection alone does not protect against the danger of mixed loads,” he added. “Surge protectors are not power-quality devices; they only protect against power surges. You can’t solve a five-dollar problem with a nickel solution.”
GROUNDING THE POWER SOURCES
The central building has a standby generator with an automatic transfer switch. The ground is not made at the generator, but rather it is made at the transfer switch. If the generator were the main power source, then the connection would be made right at the generator. Otherwise, the difference in the ground potential could destroy equipment.
MARC headquarters has two other incoming services: one for telecommunications and one for cable. The telecommunication lines are protected by gas tube arrestors as required by the FCC. Yet there was a mistake found in this installation. Both the gas tube arrestors and the cable line were bonded to the same ground bar.
“These two services should be grounded by separate home runs directly to the ground source,” West said. “Otherwise, a surge coming in on the telecom line would transfer to the cable shield and affect its associated equipment.”
Using an undersized conductor for neutral and ground prevents the SPD from functioning properly. For grounding, nothing smaller than a 4/0 should be used; but, in a large facility with a 250 MCM cable feeding a panel, the neutral and ground also should be 250 MCM. (Note: “MCM” is a wire gauge unit equal to one thousand circular mils.)
THE GROUND FIELD
West inspected the grounding at the headquarters and found it to be inadequate. The grounding had very high resistance, in excess of 200 ohms.
The new ground system was installed outside the building. This system benefited from the location of the headquarters. The Andrew lighting arrestors on the coaxial transmission line and the base of the transmission tower as well as the studio loads were bonded to a nearby retention pond, which greatly lowered the ground resistance. The original grounding cables were inadequate and were replaced by 4/0 stranded copper conductors and attached to a new ground bar. (See Figs. 3 and 4.)
The tower and the retention pond each had three ground rods that were connected by exothermic welds to 4/0 stranded copper. The three rods at the tower were driven down 70 feet and were placed about 70 feet apart. The three rods in the retention pond were 50-feet long and were placed about 50 feet apart.
The new ground system installed outside was brought into the building on about 400 feet of 4/0 stranded copper. This ground cable was connected to the two main disconnects. Insulated ground cable was used where the cable passed through the walls and above the ceilings in order to not cause any interaction between ground currents and the building steel.
THE MAIN EQUIPMENT ROOM
The tremendous amount of electronics equipment and the confluence of multiple outside services — all in the heart of lightning country — created big concerns with respect to the central building. The biggest were the “paths of destruction,” which could take down all of the equipment. The challenge was to maintain power quality and power consistency, and to prevent any of the outside wires from bringing in power surges, which could damage equipment and interrupt operations.
The main equipment room is where all the telecommunications signals come into the building (Fig. 5). This room is where the programming is routed to individual stations via microwave and T-1 lines. It is the heart of the operation, providing internet technology as well as serving as a control room. Information from the many studios in the central building (Fig. 6) as well as from myriad Internet sources is processed here.
“If this room doesn’t work, then the station is out of business,” West said. “All the processing equipment must be at equal ground potential in order to function properly and reliably.”
To ensure proper functioning and reliability, West installed a ground bar (Fig. 7) that connects all the ground conductors from every chassis. From there, the ground bar is connected to a second ground bar dedicated to a ground path for all the sensitive equipment.
ISOLATING THE POWER SOURCES
There are two sources of power in the control room. The first is for lighting and other non-sensitive circuits. The second is for critical equipment. Power is fed through a step-down transformer to a UPS system and then on to all the sensitive equipment. Should there be a power interruption, the UPS kicks in to keep the critical equipment operating and on the air (Fig. 8).
According to West, these two power sources should be treated separately. Everything on each power source must be bonded to the source’s ground.
“When we inspected the facility, we found elements of both power sources bonded to a common ground path,” he said. “More than one ground reference cannot be allowed. Everything powered through the transformer and UPS must be bonded to the transformer’s ground. Everything not powered through the transformer must be bonded to the regular utility ground path.”
Several coaxial cables coming into the facility had their shields bonded to a common ground. “That should not be allowed,” said West. “A separate ground path should be run for each coax shield. Otherwise there is a high risk of sensitive equipment being destroyed when a lightning surge seeks the path of least resistance. When ground paths are combined, the low impedance of the common ground transmits the energy to all the connections.”
Aside from the coax, the same principle pertains to modems, telephone lines and the like. They each need a home run path to ground to avoid what he terms “cross contamination.”
READY FOR SERVICE
“Once a proper lightning protection system is installed, it is as though the electrical demons have been exorcised from the radio station,” West concluded. “All new, correctly bonded ground paths have been installed using properly-sized stranded copper conductors tied to a vastly improved ground field. Furthermore, the electrical panels are appropriately segregated with correctly sized and placed surge protection.”
MARC Radio’s consulting broadcast engineer, Mark Schmucker, summed it up succinctly: “For any broadcast or telecommunication facility, I believe that any investment made in proper bonding and grounding is well worth the money spent.”
Frank Garcia agreed, “The investment in bonding and grounding is more than paying for itself. Most importantly, we are also ensuring the safety of our employees.”
David Brender is national program manager for the Copper Development Association. His duties involve directing and managing electrical programs including its Energy Efficiency and Power Quality Initiatives, building wire program, telecommunications wire, research activities, NEC and IEEE work. He represents the copper industry before such bodies as the Department of Energy. He is a Senior Life Member of the IEEE and life member of the Association of Energy Engineers, as well as a licensed Professional Engineer.