Equipment Duty for Single-Phase Devices
While performing equipment duty calculations for 1-phase devices at a 3-phase bus, you can choose to use the fault types specific to faults within the outgoing 1-phase circuit or the types of faults available for 3-phase buses.
Similarly, while performing equipment duty calculations for 1-phase devices at a 1PH-3W bus, you can choose to use the fault types specific to faults within the outgoing 1-phase circuit or the fault types available for 1PH-3W buses.
Figure 1: Short Circuit Options - Control Tab
In the Short Circuit Options dialog box on the Control tab, use the Compare 1PH Device Rating option to select which current you want to use. You can choose from the following:
- Device: This applies the 1-phase fault type and compares the device ratings with the fault currents through the 1-phase devices (see the options under Fault Type for 1PH buses). This applies to protective devices that appear in the one-line view. Devices within panels and MCCs are compared to the bus current.
- For 1PH-3W equipment you can choose between line-to-neutral fault (LN) and line-to-line fault (LL).
- For 1PH-2W line-to-neutral connected equipment, the fault type is line-to-neutral. This applies for equipment fed from 3-phase or 1PH-3W services.
- For 1PH-2W line-to-line connected equipment that is fed by a 3-phase system, you can choose between a double-line-to-ground (DLG) fault and a line-to-line (LL) fault. For line-to-line connected equipment fed from a 1PH-3W system, only line-to-line faults are applied.
- Bus: This choice applies the types of fault available at the bus. 3-phase buses can have the faults 3-phase, single-line-to-ground, double-line-to-ground, or line-to-line. You can choose the fault type for 3-phase buses from the Short Circuit Options or from the short circuit menu. 1PH-3W buses can have a line-to-ground fault or a line-to-line fault. For 1PH-3W, you can choose the fault type only from within this dialog box.
The following 1-phase fault types are available:
Note: For circuits fed by a 1PH-3W service, the fault to ground can be higher than the line-to-line fault.
Example:
Figure 2: Device Current
The figure above is a representation of a 3-phase panel. The single-pole circuit breaker at circuit number 2 is connected line-to-neutral at phase A. If a fault occurs within this circuit, only a line-to-ground fault is possible. Using the equipment duty fault type option of Device, the line-to-ground fault is applied no matter what fault type you have selected for the 3-phase panel. Circuits 8, 10 and 12 are also single-pole circuits, and are all connected phase to neutral. These are fed by the A, B, and C phases respectively. To evaluate a 3-phase fault at the load side terminals of the circuit breakers, set the option to Bus and set the 3-phase bus fault type to 3 Phase.
