Is the secondary conductor under 10 feet long or between 10 and 25 feet long? Choose Scenario 3 or 4, but choose Scenario 5 if it's an industrial installation. Is the transformer outside? Choose Scenario 2. To pick the right one, answer three easy questions: Scenario 5: Secondary conductors 10 to 25 feet long, industrial installation. Scenario 4: Secondary conductors 10 to 25 feet long. Scenario 3: Secondary conductors not over 10 feet long. Scenario 2: Outside secondary conductors. Scenario 1: Secondary conductors from a feeder-tapped transformer. That same tip applies to transformer secondary conductors, which also have five scenarios. We also described an easy way to pick the correct scenario from the five possible. When we demystified feeder taps in the previous issue, we presented the information in an arrangement that differs from what you see in the NEC. As with feeder taps, the sizing of that transformer secondary conductor depends on its length and application. The rule is the same because the physics are the same. Normally, you can use the next highest overcurrent protective device (OCPD) above the ampacity of the conductors being protected, but not with transformer secondary conductors. Basic rulesĪs with feeder taps, you can't use the “next-size-up-OCPD” rule provided in 240.4(B) for any transformer secondary conductor. Let's take a closer look at 240.21(C) to help clear up any misconceptions. Similar to feeder taps, covered in the last issue, transformer secondary conductors can be every bit as confusing.
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