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Friday, January 6, 2023
Question:
Good morning, CQD. I must replace a 500kVA, 12.47KV - 480/277V indoor dry-type transformer and since the transformers became energy efficient the replacement transformer is larger than the existing transformer that is being replaced. There is a 480V disconnect switch across from the transformer. Since a transformer is not likely to require examination, servicing, etc. while energized, what is the working clearance required from the front of the transformer to the disconnect switch on the wall in front of the transformer? Thank you for the service that you provide, Dennis DiPasquo
A
Answer:
Hello Dennis, you are most welcome, and glad to hear you enjoy the CQD. Section and Table 110.26(A)(1) provides us with the requirements for the depth of working space for installations operating at 1000V or less. Assuming the 480V disconnect switch contains fuses, it is likely to require servicing while energized working space is required. At 480V we will be using the “151-600”
Nominal Voltage to Ground row. Condition 2 will be the column used for this installation. The disconnect switch is considered the exposed live parts and the transformer, because is not likely to require servicing while energized, is considered grounded parts. The required working space depth would be 3ft 6in.