We have had discussions here previously on reducing washers and their effect on grounding paths.
Apparently there was a change in 250.92 in the '11 Code regarding these.
I was privileged to attend a seminar conducted by a UL engineer and learned a few things about reducing wishers which I thought I might share:
The information for reducing washers is located in QCRV;[FONT="][/FONT]
GROUNDING[FONT="][/FONT]
Metal reducing washers are considered suitable for grounding for use in circuits over and under 250 V and where installed in accordance with ANSI/NFPA 70, "National Electrical Code." Reducing washers are intended for use with metal enclosures having a minimum thickness of 0.053 in. for non-service conductors only. Reducing washers may be installed in enclosures provided with concentric or eccentric knockouts, only after all of the concentric and eccentric rings have been removed. However, those enclosures containing concentric and eccentric knockouts that have been Listed for bonding purposes may be used with reducing washers without all knockouts being removed.[FONT="][/FONT]
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REQUIREMENTS[FONT="][/FONT]
The basic standards used to investigate products in this category are ANSI/UL 514A, "Metallic Outlet Boxes," ANSI/UL 514B, "Conduit, Tubing, and Cable Fittings," ANSI/UL 514D, "Cover Plates for Flush-Mounted Wiring Devices," and ANSI/UL 651, "Schedule 40 and 80 Rigid PVC Conduit and Fittings."[FONT="][/FONT]
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See 250.12;[FONT="][/FONT]
Clean Surfaces. [FONT="][/FONT]
Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded shall be removed from threads and other contact surfaces to ensure good electrical continuity or be connected by means of fittings designed so as to make such removal unnecessary.[FONT="][/FONT]
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The following information comes from UL 514B;[FONT="][/FONT]
8.34 Reducing washers resistance test[FONT="][/FONT]
8.34.1 ? reducing washers shall be assembled to threaded conduit and unpainted steel plates as illustrated in Figure 16, and then subjected to the resistance test described in Clause 8.9. As a result of the test, the voltage drop shall not be greater than 10 millivolts. The samples shall then comply with the current test described in Clause 8.10.[FONT="][/FONT]
[FONT="][/FONT]
Apparently there was a change in 250.92 in the '11 Code regarding these.
I was privileged to attend a seminar conducted by a UL engineer and learned a few things about reducing wishers which I thought I might share:
The information for reducing washers is located in QCRV;[FONT="][/FONT]
GROUNDING[FONT="][/FONT]
Metal reducing washers are considered suitable for grounding for use in circuits over and under 250 V and where installed in accordance with ANSI/NFPA 70, "National Electrical Code." Reducing washers are intended for use with metal enclosures having a minimum thickness of 0.053 in. for non-service conductors only. Reducing washers may be installed in enclosures provided with concentric or eccentric knockouts, only after all of the concentric and eccentric rings have been removed. However, those enclosures containing concentric and eccentric knockouts that have been Listed for bonding purposes may be used with reducing washers without all knockouts being removed.[FONT="][/FONT]
[FONT="][/FONT]
REQUIREMENTS[FONT="][/FONT]
The basic standards used to investigate products in this category are ANSI/UL 514A, "Metallic Outlet Boxes," ANSI/UL 514B, "Conduit, Tubing, and Cable Fittings," ANSI/UL 514D, "Cover Plates for Flush-Mounted Wiring Devices," and ANSI/UL 651, "Schedule 40 and 80 Rigid PVC Conduit and Fittings."[FONT="][/FONT]
[FONT="][/FONT]
See 250.12;[FONT="][/FONT]
Clean Surfaces. [FONT="][/FONT]
Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded shall be removed from threads and other contact surfaces to ensure good electrical continuity or be connected by means of fittings designed so as to make such removal unnecessary.[FONT="][/FONT]
[FONT="][/FONT]
The following information comes from UL 514B;[FONT="][/FONT]
8.34 Reducing washers resistance test[FONT="][/FONT]
8.34.1 ? reducing washers shall be assembled to threaded conduit and unpainted steel plates as illustrated in Figure 16, and then subjected to the resistance test described in Clause 8.9. As a result of the test, the voltage drop shall not be greater than 10 millivolts. The samples shall then comply with the current test described in Clause 8.10.[FONT="][/FONT]
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