Engineers and technicians specifying hoses for hydraulic circuits routinely consider factors like pressure ratings and flow capacity. But in some instances, electrical shock is a potential risk to equipment and operators, and that demands hydraulic hoses that ensure safety when machines operate near high-voltage sources like power lines.
Thus, nonconductive hydraulic hoses are recommended for use in mobile-lift equipment like “cherry pickers,” hydraulic aerial-lift platforms, and agricultural and construction machinery. Nonconductive hoses are also routinely used in steel mills, foundries, mines and shipyards, and in rescue tools.
Users should never assume a hose is electrically nonconductive, especially if it is made of rubber. That’s because rubber compounds can vary widely in their electrical-conductivity characteristics and, therefore, can be electrically conductive, partially conductive or non-conductive. Further, some rubber hoses can be non-conductive at low voltages but conductive at high voltages. Add to that, they often have steel wires for reinforcement. And unless designed and manufactured for specific electrical characteristics, a hose’s electrical properties may change from one production run to the next.
Nonconductive hose, on the other hand, is specifically built and tested to ensure the proper electrical properties. For example, the SAE J517 standard for 100R7 and 100R8 hoses states that permissible conductivity should be less than 50 micro-amps leakage under 75,000 volts per foot of length. Such hose is, for example, built with a nylon or polyester inner tube, one or two layers of braided textile or synthetic fiber reinforcement, and cover materials like polyurethane or PVC. These typically run in sizes from 3/16 to 1 in. ID and have maximum operating pressures from around 1,000 to 5,000 psi. And they often feature an orange or other non-black cover. Some versions with multiple layers of high-tensile, aramid-fiber reinforcement can have maximum pressure ratings of 10,000 psi or higher.
Many reputable manufacturers offer 100R7, 100R8 and other nonconductive hoses to transport petroleum-based, water-based, and synthetic hydraulic fluids without a risk of conducting electricity. And they routinely engineer-in other performance characteristics like a tight minimum bend radius, excellent kink resistance, abrasion resistance and suitability for operation in temperatures from about –40° to 212° F (-40° to 100° C).
As a final note of caution: For general hydraulic systems that may contact high-voltage sources, unless a hose is specifically and clearly branded electrically nonconductive, engineers, maintenance technicians and users alike must assume that it is not.