Rules for Connection
Allowed Connections
While connecting single-phase equipment to other single-phase or 3-phase equipment, the only allowed connections are those described in Distribution Systems.
For example:
- 1PH-3W equipment cannot be directly connected to 3-phase equipment.
- A 1PH-3W connection can originate a 1PH-3W source or a center-tapped single-phase transformer.
- 1PH-3W equipment can only be fed by 1PH-3W equipment.
- A 1PH-3W source can only feed a 1PH-3W bus.
- A 1PH-2W source can only feed a 1PH-2W bus.
Single-Phase Lines
Single-phase lines such as cables, transmission lines, busways, and CL reactors do not have the option for service type like buses or sources do. The type of connection made at the upstream bus determines the service for the line.
For example:
- A single-phase cable connected to a 3-phase bus with a phase connector of BN is interpreted as 1PH-2W with a BN connection (line-to-neutral).
- If a single-phase cable is connected between two 1PH-3W buses, the cable is interpreted as 1PH-3W.
- When a single-phase cable is connected to a 1PH-3W bus with a either L1N, L2N or LL connection, the cable is 1PH-2W.
Transformers
- A single-phase transformer’s primary side (the “From” side) can only be 1PH-2W. When the center-tap check box is selected, the secondary side (the “To” side) becomes 1PH-3W; otherwise the secondary side is 1PH-2W (line-to-neutral).
- The secondary side of a center-tapped transformer can only be connected to a bus that is 1PH-3W.
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Center-tapped transformers cannot be fed from a 1PH-3W system. For example, you cannot connect two center-tapped transformers in series.
Loads, Motors, POCs, Shunts, and Capacitors
For single-phase, these equipment types are considered 1PH-2W. These can be line-to-neutral or line-to-line, depending upon the upstream phase connector.
Radial System in Single-Phase Models
For single-phase models, only radial systems are supported.
Any single-phase subsystem (contiguous block) can only be fed from one source. If it is already fed by a 3-phase system, it cannot also be fed from another 3-phase system or a single-phase source. Similarly, a single-phase subsystem cannot be fed by two single-phase sources.
A 1PH-2W subsystem can only be fed from one of the following:
- A 3-phase distribution system.
- A 1PH-3W distribution system.
- A 1PH-2W source (such as a generator or utility).
Loops in Single-Phase Subsystems
Single-phase subsystems cannot have loops within the subsystem. If there is more than one path to get from one bus to another bus within the same single-phase subsystem, the subsystem is considered to have one or more loops.
Single-Phase ATS Sources
A single-phase ATS is allowed to be fed from two sources. The ATS model is considered to isolate one source path from the other.
