The 20th and 21st centuries have seen many changes in gasoline stations. From the one-pump mom-and-pop stations with repair bays to those with bays converted into convenience stores to high-tech megastations with fuel dispensers providing food ordering, interactive computers, and television and digital sound systems with music and product ads, many of these features use closed-circuit video feeds as well as networking and display options that are interfaced through the gasoline and diesel fuel dispensers.
Old methods of determining the amount of fuel dispensed required an attendant to read and record these levels at the dispenser. The attendant used a wooden dipstick to determine the amount of fuel in each tank. Now, many fuel dispensers are provided with built-in digital recording for fuel levels with this information being transmitted to remote locations for automatic reordering. In addition, many of the in-ground fuel tank levels are monitored digitally for automatic reordering.
Most stations have multiple fuel tanks, each containing a different unleaded octane gasoline. Some dispensers can even mix the different octane from separate tanks into a hybrid combination. To accomplish this, motors at each fuel tank must be energized, causing the fuel to be mixed at the dispenser through the internal piping supplying the fuel dispenser. The controls for these motors originate at the dispenser and are connected through a computer that determines the proper amount of each level of octane from each tank.
With all this new technology, a number of safety concerns must be addressed since many of the functions mentioned above cannot or are not being de--energized during maintenance, resulting in a possible shock or explosion hazard. Existing text in 514.11 of the 2008 and previous National Electrical Codes adequately covered older technology dispensers by requiring “each electrical circuit leading into or through dispensing equipment, including equipment for remote pumping systems, shall be provided with a clearly identified and readily accessible switch or other acceptable means, located remote from the dispensing devices, to disconnect simultaneously from the source of supply, all conductors of the circuits, including the grounded conductor, if any.”
This switch or disconnecting means could be used to shut off power in an emergency, such as where a fire might be occurring at a dispenser, but could also be used as a disconnecting means for general maintenance purposes. Section 514.13 required each dispensing device to be provided with a means to remove all voltage sources, including video, audio and other similar high-tech equipment, during maintenance of the dispenser to ensure the safety of the maintenance worker and prevent inadvertent ignition of any gases or vapors at the dispenser. Unfortunately, the text in 514.13 is not as clear as it should be on exactly what voltage must be disconnected from the dispenser.
Proposals have been processed during the 2011 NEC to help address these safety concerns to disconnect all sources of power, including the limited energy sources in both 514.11(A) and 514.13. For example, Panel 14 has accepted in principle the following text: “514.11 Circuit Disconnects. (A) General. Each circuit leading to or through dispensing equipment, including all associated power, communication, data, and video circuits, and equipment for remote pumping systems, shall be provided with a clearly identified and readily accessible switch or other approved acceptable means, located remote from the dispensing devices, to disconnect simultaneously from the source of supply, all conductors of the circuits, including the grounded conductor, if any.”
Similar text has been added as follows: “514.13 Provisions for Maintenance and Service of Dispensing Equipment. Each dispensing device shall be provided with a means to remove all external voltage sources, including power, communication, data, and video circuits and, including feedback, during periods of maintenance and service of the dispensing equipment. The location of this shall be permitted to be other than inside or adjacent to the dispensing device. The means shall be capable of being locked in the open position.”
Adding very specific text addressing the types of circuits that must be shut off, either during an emergency, as covered by 514.11, or during maintenance, as covered in 514.13, should make it very clear to electricians, electrical contractors and electrical inspectors that all types of circuits supplying power to a fuel dispenser must have provisions for being disconnected without regard to the amount of voltage or current on the circuit. Video, audio and control circuits can ignite gasoline vapors and cause subsequent explosions. The voltage levels can be very uncomfortable, if not lethal, for a service technician, so care must be taken to provide the proper disconnection of all circuits at the fuel pump.
ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 and firstname.lastname@example.org.