Nipple Fill

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Nipple Fill

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Nipple Fill

The NEC allows a nipple to be filled to 60% of the cross sectional area. If all the conductors are the same size, and small, this can be a problem. Just jamming in more conductors will exceed the 60% limitation for sure. But if the conductors are large, the nipple fill allowance is usually more than will comfortably fit for any given raceway. An increase in size might be sensible. Since a nipple can not be longer than 24 inches, there is often not a problem unless an offset or 90 degree bend is included in the 24 inches.

The calculation for nipple fill is basically one of addition. Add the square inches of each conductor. Determine what 60% of the raceway in area is for the type you will use. Then subtract the conductor area from the 60% value. If there is space remaining, then the conductors will fit. If you get a number for the conductors which is larger than the 60% number, a larger conduit or fewer conductors will be needed.

There was a time in the NEC history when the type raceway did not matter. All calculations were based on trade size, period. No more. Now each raceway type has a separate table.

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