For a wye-start, delta-run connected motor, the line-side conductors on the controller side shall be based on what percentage of motor full-load current, and the conductors between the controller and the motor on what percentage?

For a wye-start, delta-run connected motor, the line-side conductors on the controller side shall be based on what percentage of motor full-load current, and the conductors between the controller and the motor on what percentage?

• A. 125% / 72%
• B. 100% / 100%
• C. 150% / 60%
• D. 110% / 80%

Answer: (A)

The key idea is that motor circuits have different current demands at different parts of the starting sequence, so conductors are sized with margins that reflect those demands. For a wye-start, delta-run motor, the line-side conductors feeding the controller must be able to handle the higher inrush and surge current that occurs when the controller closes and the motor begins to start. The standard sizing is based on 125% of the motor’s full-load current to provide a safe margin for this startup surge. The conductors between the controller and the motor, however, carry the motor current during the start in wye and the subsequent run in delta. Because of the wye starting arrangement, the effective current in these conductors is lower than the motor’s full-load current, roughly about 72% of that full-load value. This reflects the reduced current in the controller-to-motor path during the starting transition and running in the wye-delta scheme. So, the line-side conductors are sized at 125% of the motor full-load current, and the conductors between the controller and the motor are sized at about 72% of the motor full-load current.

The key idea is that motor circuits have different current demands at different parts of the starting sequence, so conductors are sized with margins that reflect those demands.

For a wye-start, delta-run motor, the line-side conductors feeding the controller must be able to handle the higher inrush and surge current that occurs when the controller closes and the motor begins to start. The standard sizing is based on 125% of the motor’s full-load current to provide a safe margin for this startup surge.

The conductors between the controller and the motor, however, carry the motor current during the start in wye and the subsequent run in delta. Because of the wye starting arrangement, the effective current in these conductors is lower than the motor’s full-load current, roughly about 72% of that full-load value. This reflects the reduced current in the controller-to-motor path during the starting transition and running in the wye-delta scheme.

So, the line-side conductors are sized at 125% of the motor full-load current, and the conductors between the controller and the motor are sized at about 72% of the motor full-load current.