Auto-sizing

Auto-sizing in the SLD editor is proposal-first. The engine recalculates recommended sizes as the design changes, but it shows those recommendations as pending suggestions before writing them to the circuit.

This page describes the current workflow: what creates sizing suggestions, what Re-size does, how acceptance works, and why some suggestions are linked.

How auto-sizing works now

The current workflow is:

You edit an electrical property, create/delete a connection, or use Re-size.
The sizing engine recalculates the affected upstream path.
The editor shows pending suggestions in green.
You review them and choose Accept, Dismiss, or Accept all.
Accepted changes are written to the components and any visible studies are marked stale and refreshed as needed.

Auto-sizing is no longer a silent "change values immediately" feature. It is a review-and-apply workflow.

Where suggestions appear

Pending sizing suggestions appear in three places:

On the canvas as green proposed values beside the current value
In the canvas header under Sizing suggestions
In the edit panel under Pending sizing suggestions

These views all refer to the same pending proposals.

What Re-size does

Re-size is the explicit action that runs the sizing flow for the selected component path and refreshes stored sizing details.

Use it when:

You want fresh sizing result cards for a component
The panel says No sizing results available
The panel says Sizing details are stale. Re-size to refresh.
You changed a component setting that affects sizing and want the latest detailed explanation

Re-size and pending suggestions work together:

Suggestions are the review layer
Re-size refreshes persisted sizing details

When you accept a bus amperage suggestion, ekx immediately refreshes that bus's stored sizing details so the bus rating and calculation card stay aligned. For cable conductor, parallel-run, transformer, and protection-device suggestions, accepting the suggestion writes the reviewed component value first. Use Re-size afterward when you need a fresh detailed sizing card for that component.

How the sizing cascade works

Auto-sizing still follows an upstream cascade from loads toward sources. The difference is that the cascade now produces suggestions for review instead of silently rewriting the branch.

A typical sequence is:

You change a load or motor input.
The branch cable serving that load is recalculated.
Upstream feeder cables are recalculated from downstream demand.
Upstream branch protection devices are recalculated from load current and conductor limits.
Breakers or fuses that protect a downstream bus are recalculated from aggregate downstream demand.
Buses may be recalculated.
Transformers may be recalculated.
Transformer primary feeders may be recalculated when transformer sizing changes.

The cascade stops at source boundaries such as utility feeds and generators. Unaffected branches are left alone.

Branch circuit vs feeder cable sizing

The cascade distinguishes between two types of cables:

A branch circuit cable connects directly to a load or motor. It is sized for that single load's current.
A feeder cable serves multiple downstream loads through buses and protection devices. It is sized based on the aggregated demand of all reachable downstream loads, applying demand factors and the continuous load multiplier at the feeder level (NEC 215.2(A)(1)).

The engine identifies feeder cables automatically based on topology — a cable whose neighbors are not terminal loads is treated as a feeder.

Branch protection vs bus protection

Protection devices follow the same branch-vs-aggregate distinction:

A branch breaker or fuse that protects one terminal load or motor sizes from that connected branch load.
A breaker or fuse whose downstream side reaches a distribution bus sizes from the aggregate demand on that protected bus.

This includes layouts where the protected bus is reached through a cable or another pass-through component. If the device is drawn as protecting a bus, ekx treats it as aggregate bus protection rather than as the first single load it can find.

What triggers a sizing preview

These changes typically refresh sizing suggestions:

Changing load or motor power (kW, HP, kVA)
Changing load current or power factor
Changing whether a load is continuous
Changing cable installation conditions (ambient temperature, conductor count)
Changing conductor material or termination temperature
Changing cable series or cable variant selection
Changing transformer rated kVA
Unlocking a previously locked component or resuming auto-sizing
Creating a new connection between components

Changes to component names, positions on the canvas, or other non-electrical properties do not trigger sizing preview.

> Note: Auto-sizing requires cables to have a cable series selected. If a cable has no series, the engine sizes the conductor but cannot apply a cable variant. A warning appears: "Cable has no series selected. Select a cable series to enable auto-sizing."

Component-level sizing modes

Each sizable component can be in one of three modes:

Auto: participates in suggestions and re-size actions
Manual: your value is preserved and suggestions stay suppressed until you resume auto-sizing
Locked: the component is frozen for sizing purposes

This is useful when you have already selected specific equipment and do not want the sizing engine to keep proposing changes.

To lock a component:

Select the component on the canvas.
In the edit panel, click the lock icon next to the sizing result.
The component now retains its current size regardless of upstream or downstream changes.

To unlock a component, click the lock icon again. When you unlock or resume auto-sizing, the editor can begin showing suggestions for that component again.

Locked components still affect the rest of the branch. For example, if you lock a cable at a specific size, the upstream protection device still uses that cable's ampacity when it calculates a breaker recommendation.

Linked suggestions

Some sizing suggestions are intentionally linked.

Example:

A breaker recommendation may be calculated using a proposed cable ampacity.
If you accept that breaker recommendation, the editor may also accept the dependent cable suggestion.

This is done to keep the accepted proposal set internally consistent.

Important distinction:

NEC rule: a breaker recommendation can depend on conductor ampacity
Editor behavior: accepting one suggestion can also apply a dependent suggestion

The linked acceptance behavior is an ekx workflow choice. It is not a separate NEC approval requirement.

Auto-parallel conductor sizing

For high-current circuits, the engine can automatically split a cable into multiple parallel conductor runs instead of selecting a single oversized conductor. This feature is enabled by default.

When a single conductor would exceed your configured maximum conductor size (default 500 kcmil), the engine tries 2, 3, or more parallel runs until it finds a configuration that keeps conductor size manageable. It enforces NEC 310.4 requirements including the 1/0 AWG minimum for parallel conductors.

You can configure auto-parallel behavior in Settings > Component Defaults > Sizing Defaults:

Auto Parallel Sizing (enable/disable)
Max Single Conductor Size (350 to 750 kcmil)
Max Parallel Runs (2 to 6)

See Auto-parallel conductor sizing for configuration details and examples.

Auto-rerun behavior

When calculation results are visible on the canvas, accepted sizing changes and other technical edits can automatically rerun studies after a short delay. This keeps displayed results current as you make changes.

Auto-rerun only reacts to changes that affect a source-connected electrical island. Editing an isolated fragment that has no utility feed, generator, or slack bus does not stale or rerun the visible study results for the energized system.

Topology changes such as adding or removing connections, creating new components, or deleting components clear the old visible study results because the network changed. If results are currently visible, ekx attempts a silent refresh after the change; if the updated topology is not solvable, run the study manually after reconnecting the system.

When to use auto-sizing vs manual sizing

Auto-sizing works best during the early design phase when load values are still changing and you want the system to keep recommendations current. Use it when:

You are exploring different load configurations
You want quick "what-if" sizing to compare options
You are building a new diagram and want NEC-compliant sizing suggestions
You want to see how a load change ripples through the system

Switch to manual sizing when:

You are in the final design phase and have selected specific equipment
You need to override a size for voltage drop, coordination, or other engineering reasons
You are matching an existing installation where equipment is already in place
You want full control over every conductor and device rating

You can mix both approaches in the same project by keeping some components in auto mode and placing others in manual or locked mode.

Sizing overview - Introduction to the NEC sizing engine
Cable sizing - Detailed cable ampacity calculations
Auto-parallel sizing - Automatic parallel conductor configuration
OCPD sizing - Overcurrent protection device selection
Sizing warnings and errors - Resolving sizing issues
Component defaults - Setting default sizing parameters