Installation Guide

© 2016 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)
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