Led Lighting Spd Design Installation Guide Page 11 LED Lighting SPD Design & Installation Guide

2015 Littelfuse LED Lighting SPD Module Design and Installation Guide www.littelfuse.com LED Lighting Surge Protection Modules Design and Installation Guide 120 V Load MOV rated for 150 V rms continuous voltage 120 V Figure 10. Loss of Neutral-Ground connection in a standard U.S. split-phase power distribution system. For example, in a standard U.S. 120V AC Line application, two 120V AC power lines (180 out of phase) are commonly fed from a center-tapped 240V transformer. See Figure 10. Let's assume a 150V-rated MOV is present in the top 120V circuit, and some load exists on the bottom 120V circuit. Both the MOV and load share the center tap, which is the Neutral-Ground connection. If a break occurs on the center tap (X-X), then the load in the bottom phase acts as a current limiter, and the line fuse may not clear. In this scenario, the 150V rated MOV is subjected to 240V at a limited current, potentially resulting in thermal runaway for the MOV. Table 44.1 in UL 1449 4th Edition defines the test voltage that should be applied to various SPD devices depending on the designer's desired device rating. (See Table 3 .) Nominal Voltage Rating Phase Test Voltage a 0-109V Single Twice Rated Voltage 110-219V Single 240 220-229V Single 380 230-239V Single 400 240-345V Single 480 346-399V Single 600 400-499V Single 690 500-1000V Single Twice Rated Voltage up to Max. 1000V 110-120V / 220-240V Split 240 120 / 208V 3-WYE 208 220 / 380V 3-WYE 380 230 / 400V 3-WYE 400 220-240 / 380-415 3-WYE 415 240 / 415V 3-WYE 415 254-270 / 440-480V 3-WYE 480 346 / 600V 3-WYE 600 400 / 690V 3-WYE 690 120 / 240V High leg delta 240 240 / 480V High leg delta 480 240V Delta c 480V Delta c 600V Delta b Table 3. Test voltage selection table (reproduced from Table 44.1 in UL 1449 4th Edition). a. For device ratings not specified in the table, the test voltage shall be the maximum phase voltage (if available) or twice the conductor pair voltage rating up to 1000V max. b. Abnormal Overvoltage Tests are not required to be conducted on 600V delta rated units, but short circuit testing shall be performed. c. The Short Circuit and Intermediate Current tests are performed at the full phase voltage. Over-voltage Testing in UL 1449 and IEC 61643-11 (continued) 11

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