Led Lighting Spd Design Installation Guide Page 10 LED Lighting SPD Design & Installation Guide

LED Lighting Surge Protection Modules Design and Installation Guide 2015 Littelfuse LED Lighting SPD Module Design and Installation Guide www.littelfuse.com MOVs are designed to clamp fast over-voltage transients within microseconds. However, in addition to short duration transients, MOVs inside SPD modules can experience temporary over-voltage conditions caused by loss of neutral or by incorrect wiring during installation ( Figure 9 ). These conditions can severely stress an MOV, causing it to go into thermal runaway; in turn, this will result in overheating, smoke, and the potential for fire. UL 1449 and IEC 61643-11, the safety standards for SPDs, define specific abnormal conditions under which devices must be tested to ensure SPD safety. Robust SPD module designs include thermal disconnects to protect the MOVs from thermal runaway. Figure 9. Temporary over-voltage conditions can severely stress MOVs, leading to thermal runaway. Over-voltage Testing in UL 1449 and IEC 61643-11 UL 1449 Abnormal Overvoltage Test In AC line applications, the loss of a Neutral-Ground connection may occur in such a way that there exists a risk that a sustained over-voltage may be applied to an MOV that is rated for a much lower continuous voltage. In an unlimited current condition, the MOV will first fail to a low impedance (few Ohms) state, but due to the high amount of energy available, it most often ruptures instantaneously. If, however, there are loads connected to the AC line that limit current flow, the MOV can overheat and potentially cause the SPD device to overheat resulting in smoke, out-gassing and eventually fire. Over-voltage Testing in UL 1449 and IEC 61643-11 10

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