National Electrical Installation Standards

Standards as High as Your Own

Friday, March 23, 2018


Can you defeat reduce the hub opening on the top of a 120v AC 30 amp disconnect from 2” to 3/4”.? I’m thinking it’s 2”. The inside diameter of the hole on top of the disconnect is 1 9/16”

Adam Hooks



Hey Adam thanks for your question. You don't say what type of wiring method is being used or where the disconnect switch is located but in general reducing fittings can be used. Fittings must usually be listed as stated in the .6 section of the applicable wiring method article in Chapter 3. A knockout diameter of 1 9/16 inches could be for a 1 1/4 inch fitting but can't be for 2 inch unless there is a new way of making the OD larger than the ID.

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