Connection rules

Electrical components must connect according to electrical engineering principles. Understanding valid connection patterns helps you build correct power system models.

Valid connection patterns

These connection patterns represent real electrical systems:

Radial distribution (most common):

Utility Feed → Main Breaker → Transformer → Distribution Bus → Feeder Breakers → Loads

Power flows one direction from source to loads.

With generation:

Generator → Breaker → Bus ← Utility Feed

Multiple sources can feed a common bus.

With redundancy:

Utility A ──┐
            ├─ Transfer Switch → Main Bus → Loads
Utility B ──┘

Automatic or manual source transfer.

Multi-level distribution:

Utility → Primary Bus (13.8kV) → Transformer → Secondary Bus (480V) → Loads

Voltage transformation between distribution levels.

Component role classifications

Components have roles that determine valid connections:

Sources (inject power):

• Utility feeds - External grid connection
• Generators - On-site generation

Distribution (route power):

• Buses - Common connection points
• Transformers - Voltage conversion
• Cables - Conductors between points

Protection (interrupt faults):

• Breakers - Resettable overcurrent protection
• Fuses - One-time fault interruption

Loads (consume power):

• Motors - Mechanical conversion
• Generic loads - Any electrical equipment

Source-to-bus connections

Sources must connect to buses (directly or through protection):

Valid:

Utility Feed → Breaker → Main Bus
Generator → Breaker → Emergency Bus

Sources provide the reference voltage (slack bus) for power flow analysis.

Invalid:

Utility Feed → Load (no bus)
Generator → Motor (direct connection)

All sources require a bus for proper power distribution and voltage reference.

Bus-to-load connections

Loads connect downstream from buses through protection:

Valid:

Bus → Breaker → Motor
Bus → Breaker → Cable → Load
Bus → Fuse → Transformer

Protection devices must exist between bus and load for overcurrent protection.

Invalid:

Bus → Motor (no protection)
Bus → Load (missing breaker/fuse)

NEC requires overcurrent protection for all feeders and branch circuits.

Protection device placement

Protection devices sit between sources/buses and loads:

Valid:

Bus → Breaker → Load (protection on load side)
Utility → Breaker → Transformer (protection on line side)

Invalid:

Load → Breaker → Bus (reversed - protection on wrong side)
Breaker → Breaker (no intermediate component)

Protection must be closer to the source than the component it protects.

Transformer connections

Transformers require connections on both primary and secondary:

Valid:

Primary Bus (13.8kV) → Transformer Primary
Transformer Secondary → Secondary Bus (480V)

Transformer impedance isolates primary and secondary voltage systems.

Invalid:

Transformer with only primary connected (no secondary load)
Transformer with only secondary connected (no primary source)

Both windings must connect for power transfer and analysis.

Cable connections

Cables conduct power between any two compatible components:

Valid:

Bus → Cable → Load
Breaker → Cable → Motor
Transformer → Cable → Bus

Cables have resistance and reactance that cause voltage drop.

Invalid:

Cable → Cable (series cables should be single cable with combined length)

Multiple cables in series should be represented as one cable with total impedance.

Voltage compatibility

Components at different voltage levels require transformers:

Valid:

13.8kV Bus → Transformer (13.8kV/480V) → 480V Bus

Transformer voltage ratings must match connected buses.

Invalid:

13.8kV Bus → 480V Load (no transformer)
480V Breaker on 13.8kV Bus (voltage mismatch)

All components on a bus must have compatible voltage ratings.

Multiple connections

Some components allow multiple connections per handle:

Buses:

• Unlimited connections on top and bottom
• Each connected component gets its own dynamic handle
• See Buses

Most components:

• One connection per handle maximum
• Breakers, fuses, transformers, loads, motors all single-connection

Cables:

• Exactly two connections (one per end)
• Cannot branch - use bus for branching

Power flow direction

Connections should follow typical power flow:

Top to bottom (conventional):

      Utility (top)
          ↓
      Transformer
          ↓
         Bus
       ↙  ↓  ↘
    Load Load Load (bottom)

This matches industry standard SLD layout conventions.

Bottom to top (generation):

    Generator (bottom)
          ↑
      Breaker
          ↑
         Bus

Generators inject power upward into the system.

Prohibited connections

The system prevents these invalid electrical connections:

Load to load:

Motor → Load (two sinks, no source)

No power source to energize the loads.

Source to source:

Utility Feed → Generator (no bus)

Sources require a bus connection point.

Circular references:

Bus A → Transformer → Bus B → Cable → Bus A

Creates unsolvable electrical loops in most cases.

Reverse protection:

Load → Breaker → Bus (protection on wrong side)

Protection must be upstream of protected equipment.

Grounding and neutral

Current version focuses on phase connections:

• Three-phase connections shown as single line
• Neutral and grounding connections not explicitly shown
• Ground fault analysis requires ground impedance modeling (future feature)

Assume proper grounding per NEC Article 250 for all installations.

Orphaned components

Components must connect to a source-fed network:

Valid network:

• At least one utility feed or generator
• All components trace back to a source
• Complete electrical path from source to loads

Orphaned (invalid):

• Components with no connections
• Components isolated from sources
• Sub-networks without sources

Run validation warnings to identify orphaned components.

Connection validation workflow

Before analysis:

1. Verify at least one source exists
2. Check all components connect to source-fed network
3. Validate voltage compatibility across connections
4. Confirm protection devices protect downstream equipment
5. Ensure transformers connect both primary and secondary

Validation warnings identify connection violations before calculations.

Related topics

• Understanding components - Component categories and roles
• Connections - Creating and managing connections
• Validation warnings - Connection validation system