CURRENT ISSUE
Contests
Test your eq
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Issue #228 July 2009
Problem 1—Jack operates an employment business of sorts and has erected a new sign in front of his establishment. It is to be operated from within his office by a DPDT switch with center off. In the up position, it will illuminate the word “WORK” on the sign with four 110-VAC bulbs, one behind each letter. The down position will light these four plus two more behind the letters “NO” or “NO WORK.” The only source of power is 220 VAC, both wires being hot with respect to ground. There are only four conductors between the switch and the sign with no other means of ground or earth return. For safety purposes, all four wires must be floating or disconnected when the switch is in the center or off position. Assuming the bulbs will be run at their rated voltage (110 VAC), how are the six bulbs wired to the four conductors? No other components, active or passive, are used.
Problem 2—So, with this solution, what happens if one of the bulbs burns out?
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