…And no one noticed! / System Designed by Florida Company / The Principals 

A: None of the above…when the building's electrical system is protected by a proper copper grounding system. Here's what actually took place at a major Florida bank.

The bank operates a state-of-the-art data center (Figure 1) near its Tampa headquarters (cover). The center is housed in a single-story, 5,000-sq ft (500-sq m) cinderblock building that had once been a warehouse. Before moving in, Suncoast gutted the old structure completely and rewired it top-to-bottom for sensitive electronic equipment. Telephone equipment is housed in a separate building to diminish the risk of total system failure in the event of a severe lightning storm.

Suncoast management was also aware that the data center is located in the most lightning-prone city in the country and that one hit could bring their entire system down. To minimize that risk, the bank installed a low-resistance, heavy-gage copper grounding system, along with multi-layer surge protection. The cost of added protection was minimal, especially when compared with the value of the equipment being protected - not to mention the risk of lost data and possible downtime.
But no matter what the cost, the investment in a little extra copper paid off handsomely for Suncoast on the day the lightning struck…

Earl Brendle, Suncoast's vice president, facilities, was working in one of the bank's branches when he got a call from the data center. As Brendle recalls, "The data center has a 250-kW emergency generator and transfer switch to keep us on line whenever we lose utility power for extended periods. Last year, one of the center's technicians stepped outside about half an hour after a storm passed and noticed that the generator was running, and would I please stop by to reset it.

"When I got to the data center, the generator was still powering the building. That seemed odd, because if the generator had kicked in due to an outage, it should have shut down once utility power was restored.

"Then I saw the meter, or rather, the mass of burned metal and insulation that was left of the meter socket (Figure 2a). Lightning had struck our 480-V service entrance cable. It blew the meter off the wall (we never did find it) and headed straight for the transfer switch and generator.

"The amazing thing is that no one in the center even knew we were hit! The lights flickered a bit, but that's not unusual around here. Thinking back on it, what was really scary was that all of our very expensive data processing equipment and a lot of important financial data could have been destroyed in an instant. Instead, the center just kept on working as if nothing had happened."

Figure 5b. Shows the corrosion-resistant bronze clamp that bonds the 4/0 grounding conductor to the generator base.

The protection system that saved Suncoast's equipment and data was designed and installed under the supervision of Power & Systems Innovations, Inc. (PSI), an Orlando-based company that specializes in protecting sensitive installations like the Suncoast data center. Because much of their work is done in the heart of Florida's famous "lightning alley," PSI has developed its own stringent specifications for commercial grounding systems. The power-quality provisions of those specs go well beyond the National Electrical Code® (NEC).

Figure 3. shows a partial schematic of the system PSI designed for Suncoast. Starting from the ground up, its main elements include:

• Three 20-ft x 5/8-in (6-m x 16-mm) copper-clad-steel grounding electrodes located at the service entrance (Figure 4a), between the emergency power generator and transfer switch (Figure 5a), and in a lot behind the building, respectively. Ordinarily, PSI would have preferred to install a buried, heavy-gage copper ring-ground around the building, but property constraints dictated the electrodes' location. The three electrodes PSI installed replaced a single galvanized rod left over from the building's warehouse days. The electrodes are exothermically bonded to a buried, bare 4/0 copper grounding electrode conductor leading from the main service entrance panel (Figure 4b). Other buried 4/0 copper outside the building connects the electrodes and the service entrance with the A/C panel and dual A/C units (Figure 6).
  
  The grounding system's resistance to earth as measured by fall-of-potential testing is 4.3 ohms. That's comfortably within the 1- to 5-ohm range considered suitable for commercial buildings under the Institute for Electrical and Electronic Engineers Standard 142, IEEE Recommended Practice for Grounding Industrial and Commercial Systems - The Green Book.
  
  
• Another 4/0 copper grounding conductor connects the ground-neutral bus in the service entrance panel to the ground bus in a 480-V distribution panel in the building's electrical room (Figure 7). The bus serves the building's two 480-V air conditioning units (one is a back-up), a 277-V lighting circuit and the primary of the building's 480 - 208Y/120-V transformer.
  
  The transformer feeds two 120/208-V, 300-A distribution panels (Figure 8). One of the panels supplies power to the data center's main computer room, which houses the center's host computer, several servers and a variety of other sensitive equipment (Figure 9). The other panel feeds branch circuits to workstations and remaining outlets throughout the building.
  
  

• Multiple uninterruptible power supplies (UPSs): Two standalone 16-kVA UPS units serve the main computer room (Figure 9). Smaller units are found at individual workstations. The primary UPS is redundant in both electronics and batteries.
  
  
• Up to seven layers of voltage surge protection. A TVSS is installed on the transfer switch; another is located at the main 480-V bus. Additional TVSSs protect each of the two120/208-V subpanels, including circuits serving the UPS units for the main computer. (Thus, both primary and secondary sides of the transformer are surge-protected.) Each of the air conditioning disconnects is individually surge-protected, and two branch circuits serving fire alarm and fire call circuits, respectively, are protected by additional TVSS units at the distribution panel. Surge strips are plugged into wall outlets where needed in the building. Finally, small units located at workstations contain surge suppression circuitry to protect individual computer terminals.
  
  

That's essential, as PSI's president, John West, points out. "High-quality surge suppressors are very effective protection devices," he says. "But even the most expensive TVSS you can buy is absolutely useless unless it sees a high-quality, low-resistance ground. And by high quality, I don't just mean meeting Code requirements for low impedance between outlets and the ground-to-neutral bus. Our specifications call for less than five ohms total resistance to earth, especially where there's sensitive equipment involved. We won't accept a job unless our customer agrees to that."

In addition to low-resistance grounding and heavy-gage copper conductors, PSI's specifications require that all bonds be made either with exothermic welds or copper-base (brass or bronze) mechanical clamps, as appropriate to the location. Copper and copper alloys, such as brass and bronze, resist corrosion, so joint resistance remains low over long periods of time. For added protection, PSI grinds all mating joint surfaces to bare metal and coats them with conductive grease before clamping. Mechanical bonds made with copper connectors also remain tight indefinitely and don't have to be re-torqued periodically to avoid loss of continuity.

"We also prefer copper-clad electrodes except in locations where the soil is very acidic," says PSI's West. "We never use galvanized steel electrodes, and when it comes to conductors, we never use anything but copper. It's one reason why we haven't had any of our clients lose a single piece of equipment during the ten years we've been in business."

Earl Brendle knows that the Suncoast Schools FCU is one of those satisfied clients. "If someone asks me how they should protect their equipment, I tell them to do what we did: install a good grounding system and multiple layers of surge protection. Then, if their facility gets hit by lightning, they'll probably be as fortunate as we were, and no one will even know it happened."