Conductor sizing for multiple hermetic compressors must include total load plus what percentage of the largest motor's full-load current?

Conductor sizing for multiple hermetic compressors must include total load plus what percentage of the largest motor's full-load current?

• A. 50%
• B. 25%
• C. 100%
• D. 75%

Answer: (B)

When several hermetic compressors share a single conductor, you size for the combined running current plus a small allowance for the largest unit’s starting draw. The standard approach is to add up all the full-load currents and then add a portion of the largest motor’s full-load current. That portion is 25%. This provides enough capacity for typical simultaneous operation and the starting surge of the biggest motor without overpadding the conductor. For example, if the compressors have full-load currents of 6 A, 8 A, and 10 A, the total running load is 24 A. The largest motor is 10 A, and 25% of that is 2.5 A. Adding gives 26.5 A, which is the conductor capacity you’d size for. So the extra amount added to the total load is 25% of the largest motor’s full-load current.

When several hermetic compressors share a single conductor, you size for the combined running current plus a small allowance for the largest unit’s starting draw. The standard approach is to add up all the full-load currents and then add a portion of the largest motor’s full-load current. That portion is 25%. This provides enough capacity for typical simultaneous operation and the starting surge of the biggest motor without overpadding the conductor.

For example, if the compressors have full-load currents of 6 A, 8 A, and 10 A, the total running load is 24 A. The largest motor is 10 A, and 25% of that is 2.5 A. Adding gives 26.5 A, which is the conductor capacity you’d size for.

So the extra amount added to the total load is 25% of the largest motor’s full-load current.