Airport Fueling Systems Isolation/Bonding
Airports utilize underground piping to transport large amounts of jet fuel, and this critical infrastructure requires cathodic protection to prevent corrosion. Since cathodic protection systems utilize insulated joints to sectionalize the piping, arcing at insulated joints presents a hazard to system operation and personnel, whether due to AC fault current, lightning, or static buildup.
A separate problem exists where the grounding conductor on motors or other electrical equipment on a cathodically protected pipeline shorts the CP system to the copper grounding system, resulting in inadequate levels of cathodic protection. While the grounding conductor is required by code, a means of addressing the CP current flow on this conductor is needed.
Over-voltage protection of the insulated joints can be accomplished using Dairyland devices that are UL listed for hazardous locations. Most common has been the model OVP, which was developed in conjunction with the US Army Corp of Engineers to meet their need for a listed Class I, Division 2 product. The OVP, which is also certified for Division 1 hazardous locations, is specified by the Corp of Engineers for worldwide use for US military airport applications (see USACE Specifications). The newer model OVP2 now addresses Division 2 locations, while the OVP is used for Division 1 sites requiring explosion proof construction.
Where grounding conductors affect the CP system, the Dairyland model PCR has been most commonly used, although the SSD, with its compact design is also an option. The device is placed in series in the grounding conductor (and conduit if needed) to block the flow of DC current, while acting as a low impedance path to AC current. The devices are UL listed for meeting the electrical codes in the US and Canada for placement in a grounding conductor. See the schematic of a sample installation.
Insulated joint protection using an OVP
Select the OVP model with the FMFB mounting option, or the OVP2 with the MTF mounting option, if using the flange bolts for mounting the brackets. For other mounting methods, see the product literature. Specify the hole size needed for the FMFB or MTF mounting kit. This hole diameter should allow for the flange bolt and insulating sleeve, plus clearance. Usually this value is 1/8" larger than the bolt diameter.