Buses

Buses represent electrical connection points in your power system where multiple components connect. They are the fundamental building blocks for distributing power to loads and connecting generation sources.

What buses represent in electrical systems

In electrical power systems, a bus (or busbar) is a conductor or group of conductors that serves as a common connection point. Power enters the bus from sources (utility feeds, generators, transformers) and exits to loads or downstream distribution.

Buses appear as horizontal lines on single-line diagrams, with components connecting vertically from above or below. This matches industry-standard SLD conventions.

Creating a bus

Drag the Bus icon from the component toolbar at the bottom of the canvas.
Drop the bus where you want it positioned.
The bus snaps to the 50px grid automatically.
Configure bus properties in the edit panel (voltage, amperage, ratings).

The bus starts with minimum width and expands as you connect components.

Slack bus designation

Power flow needs a reference source (also called the slack or swing bus). The reference:

Provides the reference voltage angle (0 degrees)
Balances system real and reactive power
Absorbs power flow calculation errors
Typically represents the utility connection point

You do not designate the slack bus yourself. Each utility feed is a reference source. In any part of the diagram that no utility feed reaches, such as a panel a transfer switch has moved to its generator, the largest in-service generator in that part becomes the reference. Power flow cannot run without a utility feed or generator.

Rated voltage and amperage

Rated voltage:

Nominal system voltage in kV
Example: 0.48 for 480V system
Affects power flow calculations and voltage drop analysis
Should match connected equipment ratings

Rated amperage:

Maximum current capacity of the bus in amperes
Based on busbar size and construction
Example: 1200 for 1200A main switchboard
Does not affect power flow, but it is used by sizing as the protected-equipment rating

Set appropriate voltage for all buses to enable accurate power flow analysis.

Bus auto-sizing floors

Bus auto-sizing starts with aggregate downstream demand, then applies any bus sizing margin. It also preserves two equipment-rating floors:

directly attached terminal equipment, such as a panel-like load connected directly to the bus
upstream main breakers or fuses that protect the bus

Auto-sizing also applies the configured voltage-class minimum bus rating before selecting the nearest standard amperage:

buses at or below 1 kV use Minimum LV Bus Rating (system default: 100 A)
buses above 1 kV use Minimum MV/HV Bus Rating (system default: 600 A)

The selection then uses the effective Allowed Bus Ratings from Settings → Sizing Rules. Unchecked ratings are skipped by auto-sizing; manual bus ratings and existing buses are not changed by this availability setting.

The upstream protection floor means a bus may be proposed larger even when the bus sizing margin is 0%. For example, if aggregate demand requires a 225 A main breaker, the protected bus must also be at least 225 A unless the bus is manual or locked.

If the bus is Auto, ekx proposes the required bus rating. If the bus is Manual or Locked, it becomes a hard limit for the upstream main breaker instead.

Dynamic handle system

Buses use a unique dynamic connection system that differs from other components:

Handle generation:

Handles are not fixed positions
Each connected component gets its own handle
Handles align vertically with the connected component's position
New connections create new handles automatically

Why dynamic handles:

Allows unlimited connections to a single bus
Maintains vertical connection lines (industry standard)
Bus width adjusts to accommodate all connections
Provides intuitive drag-and-drop workflow

You never manually position bus handles - they automatically align with connected components.

Vertical connection behavior

When you connect a component to a bus:

The component's connection handle aligns vertically with the bus.
The bus creates a connection handle at the exact horizontal position of the component.
Connection lines run perfectly vertical between component and bus.
The connection line remains vertical even if you move the component horizontally.

This vertical alignment matches electrical SLD conventions where buses are horizontal and connections are vertical.

Asymmetric expansion

Buses expand and contract based on connected component positions:

Left-side expansion:

When you drag a connected component to the left of the bus left edge, the left side extends to accommodate it.
The right side of the bus stays fixed in place.
This provides visual feedback that you're expanding the bus to the left.

Right-side expansion:

When you drag a connected component to the right of the bus right edge, the right side extends.
The left side stays fixed.
Intuitive feedback for right-side expansion.

Contraction:

When you delete or move a component that was at the leftmost or rightmost position, the bus contracts.
The bus always spans exactly from the leftmost to rightmost connected component (plus small padding).

This asymmetric behavior makes editing feel natural - the side you're working on expands while the opposite side stays anchored.

Bus width calculation and layout

The visible bus line width is determined by connected components:

Bus Line Width = (Rightmost Component X) - (Leftmost Component X) + Padding

Minimum width:

Buses have a minimum width even with no connections
Prevents buses from collapsing to invisible size
Allows room for future connections

Maximum width:

No maximum width limit
Bus can span the entire canvas if needed
Common for main distribution buses with many feeders

Label space:

Bus label appears to the right of the bus line
Container width accounts for label space
Label does not affect electrical connection points

The bus container may be wider than the visible line to accommodate the label, but connection handles are positioned based on the electrical line, not the label.

Configuring bus properties

Select the bus to open the properties panel:

Name
Voltage and Amperage
Phase/Wire
Equipment class and Enclosure rating
Short-circuit ratings (Sym., Asym., Peak) and Bus bracing
Fault for short circuit and arc flash
Arc flash geometry (IEEE 1584-2018): electrode configuration, electrode gap, working distance,

and enclosure size

Accepted duration, on the Study tab: an arc flash duration you accept for this bus (see

Running an arc flash study)

Description

Each field saves when you leave it, except the accepted duration, which saves when you select Accept.

Common bus configurations

Single bus system:

One main bus receives utility power
All loads connect directly to main bus
Simple but no redundancy
Used in small facilities

Main-tie-main configuration:

Two main buses (Bus A and Bus B)
Normally open tie breaker between buses
Each bus fed from separate source
Allows load transfer during maintenance

Distribution bus hierarchy:

Main switchboard bus (480V or 13.8kV)
Feeder buses at load centers (480V)
Branch panel buses (120V, 208V)
Follows power distribution from source to loads

Connecting components to buses

To connect manually:

Click and drag from a component's connection handle.
Drop on the bus.
The bus creates a handle at the drop position.
A vertical connection line appears.

To connect via auto-connect:

Drag a component from the toolbar.
Drop it within 300px of a bus.
The system auto-connects if electrically compatible.
The bus handle positions at the component's horizontal location.

To disconnect:

Click the connection line to select it.
Press Delete key, or
Right-click the connection line and select Delete.

See Connections for detailed connection workflows.)

Bus annotations and results

After running power flow analysis, buses display voltage annotations:

Voltage magnitude (per-unit or kV)
Voltage angle in degrees
Color-coded severity (green, yellow, red)

See Interpreting power flow results for annotation details.)

Common issues

"Bus has no connections":

Warning appears if bus exists but nothing connects to it
Orphaned buses don't affect calculations but add clutter
Either connect components or delete unused buses

"Bus voltage mismatch":

Connected components have different voltage ratings
Verify transformer voltages match bus voltages
Check for incorrectly configured equipment

Connections - Creating and managing connections
Transformers - Connecting transformers to buses
Cables - Running cables between buses
Power flow analysis - Analyzing bus voltages