When inspecting a small office facility for a customer, I was surprised that he had a fuel cell system for his main power source that was backed up by an optional standby generator system. In other words, the complex did not depend on utility power. I thought this installation concerning power systems completely independent of the utility was very interesting and well worth discussing in ELECTRICAL CONTRACTOR.
Believe it or not, fuel cell technology was first introduced in the 1800s, but modern technology has made these systems more reliable. Therefore, it is plausible, as more information concerning these units becomes available, more of these systems will be used to provide power to small facilities that require only small amounts of electricity. Having said that, facilities requiring larger amounts of power are already using fuel cell technology to supply lighting and other power-operated equipment.
Selecting a fuel cell system
For the purpose of this article, the fuel cell system was connected where there was an abundance of natural gas, and the unit was capable of delivering about 278 amps. The service equipment and overcurrent-protection device (OCPD) supplying the facility had a rating of 250 amps. Therefore, with diversity the three-phase, four-wire, 100-kW fuel cell distribution unit had more than enough capacity to handle the connected loads. The fuel cell system complied with Article 692, which regulates its installation.
Conductors, as required in 692.8(B), were routed from the fuel cell system to the premises wiring system and were sized not less than the nameplate’s rated circuit current and compatible with the fuel cell system’s OCPD. Because the nameplate allowed 300 kcmil, THWN copper conductors to supply the unit, these size conductors were installed.
The fuel cell was equipped with an OCPD that was capable of protecting the circuit conductors supplying the loads of the facility. Additional OCPDs were not required, but if they are installed, they must be readily accessible to the user per 230.70(A)(1) and 240.24(B).
A disconnecting means for the fuel cell system was installed and meets the provisions of 692.14 that require the disconnecting means to comply 225.31 and 225.33 through 225.40. Such a disconnect was not required to be rated for service equipment use, according to 230.66. The fuel cell was equipped with manually operated switches as well as circuit breaker(s) that were accessible to the user. Sections 692.9(C) and 692.56, under certain conditions, requires warning signs to be placed at the location of the disconnect(s) and the placement of the signage was found to be acceptable.
Optional standby system
An optional standby generator was installed as a backup power source in case the fuel cell system should fail or is timely shut down for periods of maintenance or repair problems. The generator set was installed as a separately derived system and cabled to and from the transfer switch and to the service equipment with wiring methods selected and installed from Chapter 3 in the National Electrical Code (NEC). Grounding and bonding was performed at the generator as required in 702.10(A) and 250.30. As NEC requires, the generator was sized to carry the calculated full load of the facility in accordance with 702.5(B)(2), 225.3(B) and 215.2(A)(1).
Point of connection
Section 692.65(A) and (B) permits the fuel cell system power source to be connected to the supply or load side of the service-disconnecting means. The conductors of the fuel cell system were connected through the transfer switch and routed to the service-equipment disconnecting means that was listed for service-equipment use. Information on feeders can be found in Article 225 that governs feeder requirements that are connected to the load side of the service-distribution- disconnecting switches.
A transfer switch was installed to transfer from fuel cell power to optional standby power. Isolation was properly maintained between the protection and the distribution power of the fuel cell system and the standby generator’s power source. The transfer switch can be installed externally or internally
to the fuel cell unit, and this requirement was complied with by being installed externally.
Since backup power was provided by an optional standby system, the transfer switch had to meet the sizing requirements of 702.5 as well as comply with 695.59. Inspection of the installation proved this to be the case.
Due to deregulation of the utilities and greater cost to obtain electrical power from small distribution lines or for facilities located in rural areas, facilities using small amounts of electricity are turning to alternate power sources as described in this article. And many facilities are selecting these sources so as to be independent from utility power. Be prepared to inspect or wire this type of installation.
STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the NEC and OSHA, as well as other standards. Contact him at 817.581.2206.