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Varistor - Slide17

The Abnormal Overvoltage, Limited Current test was derived to address a condition where there is a loss of neutral. For example, in a standard US 120VAC Line application, two 120VAC power lines (180° out of phase) are commonly fed from a center-tapped 240V transformer. For this example, 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 run away for the MOV.

PTM Published on: 2012-08-31