Hanging hardware (e.g. nozzles, hoses, swivels, breakaway couplings) must be conductive in order to dissipate any static charge that is generated while fuel is being dispensed.  Conductivity of any product is obtained by either a metal-to-metal contact path from inlet to outlet or by the use of non-metallic electrically conductive materials (e.g. rubber formulated for use in fuel hoses).  Since conductivity is important to public safety, these components are tested to a maximum resistance by certifying bodies such as Underwriters Laboratory (U.L.) and Underwriters Laboratory of Canada (U.L.C.) as recommended by the national fire codes.  Both U.L.^1,2,3 and U.L.C.⁴ require that the electrical resistance of individual nozzles, swivels, and breakaway couplings not exceed 500,000 ohms (0.5 meg ohm) and hoses should not exceed 70,000 ohms per foot.  

To obtain accurate resistance measurements, it is recommended that a megohmmeter⁵ capable of  a test voltage of 500 volts direct current (Vdc) be used.  This test voltage is required by both the UL 330¹ and ULC-S644-00⁴ standards and the NFPA 77 – Static Electricity ^5,6 code.  As noted in NFPA 77, Section 1.8.2⁶   “Tests of the high-resistance paths should be made with an applied potential of 500 volts or more, in order that a minor interruption (paint or grease-film or air gap) will be broken down and a correct reading of the instrument obtained.” 

A 500 volt test is an established industry standard.  The condition of the metal-to-metal contact is of such a nature that a standard low voltage ohmmeter (3 to 9 volts) may or may not show continuity of the product that is continuous.  For example, small gaps from pipe sealant, lubricants or the use of non-metallic electrically conductive materials, may lead to poor or intermittent readings on a low voltage ohmmeter (3 to 9 volts).  Therefore, a low voltage ohmmeter may lead to faulty or inconsistent results, whereas a megohmmeter set at 500 Vdc will give more consistent results.  It is recommended that a megohmmeter capable of 500 Vdc with a resistance range of 500,000 ohms be used.  Use of the low voltage meter may result in the unnecessary replacement of products that will dissipate static charges.

REFERENCES

1. UL 330, Hose and Hose Assemblies for Dispensing Flammable Liquids, Sixth Edition, May 27 1999.
2. UL 567, Pipe Connectors for Petroleum Products and LP-Gas, Eighth Edition, June 7 1996.
3. UL 842, Valves for Flammable Fluids, Eighth Edition October 28 1999.
4. ULC-S644-00, Standard for Emergency Breakaway Fittings for Flammable and Combustible Liquids, June 2000.
5. NFPA 77, Recommended Practice on Static Electricity, 2000 Edition, Section 5.8.4 Page 77-13, Appendix D Page 77-53 Definition D.1.39.
6. NFPA 77, Recommended Practice on Static Electricity, 1993 Revision, Section 1.8.2, Page 77-7.