Auto-sizing

Auto-sizing in the SLD editor is proposal-first. The engine recalculates recommended sizes as the design changes and represents those recommendations as sizing proposals. Depending on the project mode, EKX either shows proposals for review or applies the same proposals automatically.

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

How auto-sizing works now

In Suggest mode, sizing waits for your review:

You edit an electrical property or create/delete a connection.
The sizing engine recalculates the affected upstream path.
The editor shows pending suggestions in green and a sizing bar at the bottom of the canvas.
You review them and choose Accept (for example Accept 6 A), Keep (for example Keep 70 A), or Accept all. Keep leaves the current value in place until the inputs change again.
Accepted changes are written to the components and any visible studies are marked stale and refreshed as needed. The bar shows what was applied with an Undo control until your next edit.

New projects run in Auto-apply mode. In that mode, EKX uses the same preview and proposal-apply checks, but writes eligible proposals automatically after an SLD edit or a REST API import. If a proposal cannot be applied safely, EKX leaves it in the review UI instead of hiding it.

Project-level auto-sizing mode

New projects start in Auto-apply. A duplicated project keeps the mode of the project it was copied from, and existing projects keep their mode.

To change the mode for a whole project:

Open Diagram Settings.
Select Project Settings.
Set Auto-sizing to Off, Suggest, or Auto-apply.

Modes:

Off turns sizing off for projects you size entirely by hand. The editor shows no suggestions, no Re-size system control, no Sizing tab, no selection checks and no lock buttons or lock icons, on the canvas or in exported drawings. The sizing evidence report is not offered, although saved sizing reports still download. Server-side auto-sizing writes are blocked. Nothing stored is removed: ratings, saved sizing results and component Auto/Manual/Locked settings return when you switch back to Suggest or Auto-apply. A rating, size or conductor you enter by hand is marked Manual, and sizing does not change it after you turn sizing back on.

> Warning: With sizing Off, the editor shows no voltage-drop, undersized-conductor or protection-mismatch warnings. Power flow analysis bus voltages are still shown.

Suggest shows sizing proposals on the canvas, in the sizing bar, and in the edit panel. You choose Accept, Keep, or Accept all before values change.
Auto-apply runs the same proposal flow after eligible edits and applies safe proposals automatically. Each run reports once in the status bar at the bottom of the editor, for example "Auto-sizing updated 2 components · TX-001, BUS-001", with Undo. The message stays in Messages, so its Undo stays available after newer messages. Changed components use the same sizing-change highlight used by Re-size system.

Selected protection equipment

A selected part remains linked to its actual ratings. When sizing recommends a different protection current, EKX first checks for a supported trip adjustment on the installed equipment. If an adjustment cannot meet the recommendation, it looks for an equivalent part in the same series. This works for both larger and smaller recommendations.

For example, accepting a 25 A recommendation for an AJT60 fuse selects the matching AJT25 when available. If no suitable part exists, EKX keeps the installed part, rating, settings and curve unchanged. Open the recommendation to choose a replacement or explicitly use generic equipment. Generic equipment has no manufacturer curve or implied catalogue capabilities.

Settings > Profile > Automatic protection updates controls part replacement and trip adjustment across your projects. It is on by default. Turning it off blocks those changes through automatic sizing and Accept all; you can still review and accept an individual device. Project Off and equipment locks always block sizing writes. Selecting a part does not lock the device.

In Suggest mode, ordinary edits leave protection recommendations pending. Re-size system is a separate explicit acceptance: it refreshes the plan and applies every acceptable suggestion with its required protection and conductor changes as one change. If a required change needs your decision or cannot be completed, EKX leaves that group unchanged and identifies the blocker. In Auto-apply, eligible changes can also follow an electrical edit; opening the project, refreshing a panel or changing this preference does not apply sizing.

Use Undo to restore an accepted sizing change, including its part, settings, curve and dependent equipment. Saved changes are also available under Activity > Sizing history after reopening the project. If the affected equipment has since changed, EKX asks you to review the conflict instead of overwriting it.

Where suggestions appear

Pending sizing suggestions in Suggest mode appear in three places:

On the canvas as green proposed values beside the current value. Click the value to accept it, or the x that appears on hover to keep the current value
In the sizing bar at the bottom of the canvas
In the edit panel under Sizing suggestion

These views all refer to the same pending proposals and use the same wording.

Each suggestion shows the device, the change (for example 70 A → 6 A), and one sentence saying where the size comes from, such as the motor it protects or the demand on the bus it feeds. Why 6 A? opens the arithmetic and limits behind it. A warning line appears only when accepting changes more than the number, for example when no part in the selected series is rated for the new size and the part would be removed.

When there is one plain suggestion, the sizing bar shows it and you decide there. With several, the bar shows how many devices need review and whether any need a part choice or missing input. Review opens the list in this order: components that need input before they can be sized, devices that need a part choice, changes ready to accept, blocked changes, voltage-drop checks, and applied changes.

Changes that only work together, such as the cables on one load's voltage-drop path or a main breaker with the bus and feeder it protects, appear as one card with a single Accept and the note "Applied together or not at all".

In Auto-apply mode, proposals usually do not remain pending. Like Re-size system, each run repeats until nothing acceptable is left, so a change that makes room for the next one is followed through. After EKX writes them, the status bar names the changed components with an Undo control, and Messages keeps each run's message. Nothing covers the drawing. If EKX cannot safely apply a proposal, that proposal remains pending for review.

What Re-size system does

Re-size system is the one explicit sizing action. It recalculates the whole project and accepts every acceptable suggestion, with its dependencies, as a change you can undo in one step. Because one accepted change can create the next (a smaller motor breaker can allow a smaller transformer, which resizes its secondary), it repeats the calculate-and-accept round until nothing acceptable is left, up to three rounds, and one Undo reverses them all. If changes are still waiting after the third round, EKX says how many so you can review them or run Re-size system again. It applies in both Suggest and Auto-apply modes, then refreshes the stored sizing details. Find it in the project header, to the left of the study buttons; on a phone it is Re-size in the bottom action bar. It is unavailable in a scenario, so switch to the baseline to use it.

Use it when:

You want the system sized now rather than reviewing suggestions one at a time
The panel says No sizing results available
The panel says Sizing details are stale.
You changed a component setting that affects sizing and want the latest detailed explanation

Re-size system and pending suggestions work together:

Suggestions are the review layer; each card still offers Accept and Keep for one change
Re-size system is your instruction to apply everything valid now, including suggestions you previously kept
A transformer group includes its required primary and secondary protection and conductors
If any required change is blocked, none of that dependent group is applied

Recheck the current selection

Use Recheck when you need to evaluate the equipment currently installed in the diagram. The check reads the current project and scenario facts and does not write component values, sizing modes, settings, or historical sizing results. It is not shown when project auto-sizing is Off; the REST API check endpoint still runs it on request.

The check evaluates Auto, Manual, and Locked components. Manual and locked values are not treated as failures merely because they differ from a recommendation. A recommendation is listed separately, and a conditional recommendation can require dependent equipment changes before it can be applied. If the check cannot establish a requirement because inputs or support are missing, it reports review or unavailable status instead of a pass.

Scenario values are hypothetical. A scenario check evaluates its effective overrides and shows the inherited base selection mode; it does not change the base rating, part, or mode.

When you accept bus, cable conductor, cable parallel-run, protection-device, or transformer suggestions, ekx refreshes the affected stored sizing details after writing the reviewed values.

How the sizing cascade works

Auto-sizing still follows an upstream cascade from loads toward sources. The cascade produces proposals first; project mode decides whether those proposals wait for review or are applied automatically.

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 together with their required primary and secondary protection.
Transformer primary and secondary conductors may be recalculated when transformer sizing changes.

The cascade stops at source boundaries such as utility feeds and generators. Unaffected branches are left alone. Changes that depend on the same transformer are accepted as one group, so a blocked protection device or conductor cannot leave an earlier transformer or feeder change behind.

Auto-sizing uses the effective electrical topology, not every line drawn on the canvas. It ignores non-electrical connections, open connections (including open ties), and components marked out of service before it looks for downstream loads, upstream feeders, main breakers, buses, or transformers. This lets you keep control links, maintenance-open equipment, and spare ties on the one-line without having them accidentally contribute to sizing.

Scenario sizing applies component overrides before this topology check. For example, a scenario that marks a cable or load out of service removes that component and its connected path from sizing for that scenario only. Connection-level scenario switching overrides are not part of the current workflow; ordinary auto-sizing is not a worst-case envelope across multiple switching states.

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. Non-motor loads use the explicit diversity × demand × utilization factor, followed by feeder-level continuous-load treatment. When motors are present, the conductor also enforces NEC 430.24: 125% of one largest motor FLC, all other motor FLC, 100% of noncontinuous non-motor load, and 125% of continuous non-motor load.

New general loads use a unity demand factor by default. Reduction factors should represent an intentional project/load assumption; ekx does not apply a generic 75% reduction to newly created loads.

Aggregate sizing also checks voltage context. If a 208 V three-phase load is drawn directly on a 480 V bus with no transformer, ekx leaves the existing ratings unchanged and reports the missing voltage boundary. Common 277 V line-to-neutral loads on 480Y/277 V and 120 V loads on 120/240 V remain valid.

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

Direct bus-to-load equipment floors

Some one-lines use a bus directly connected to a load or motor as an ETAP-style label point for terminal equipment such as a panel, MCC, switchboard, or packaged load. ekx accepts this shortcut without requiring a separate checkbox.

When a terminal load or motor is connected directly to a bus, bus auto-sizing preserves the directly attached equipment rating while still using aggregate demand for the rest of the downstream network. It starts from:

aggregate downstream demand, including demand factors and the bus sizing margin
the connected rating of the directly attached terminal equipment
the configured voltage-class minimum bus rating: Minimum LV Bus Rating for buses at or below 1 kV, or Minimum MV/HV Bus Rating for buses above 1 kV

For example, a 200 A panel-like load at 50% demand contributes 100 A of aggregate demand, but a directly connected bus will add back the 100 A shortfall so the panel is still represented at 200 A. If the same bus also feeds modeled branch loads, those branches keep their normal aggregate-demand contribution. If the same load is reached through modeled branch equipment, such as bus -> breaker -> cable -> load, the bus uses the normal aggregate-demand basis.

Main breaker and bus rating coordination

A main breaker protects the bus downstream of it. That means the protected bus rating must be at least the selected main breaker rating.

When both components are in Auto mode, ekx makes that decision automatically:

the main breaker sizes from aggregate downstream demand
breakers and switches above 1 kV apply the configured Minimum MV/HV Breaker and Switch Rating. A new breaker or switch placed or connected above 1 kV starts at this rating instead of 400 A, unless it has a catalogue part or a rating you set
the main breaker margin is applied when protected equipment and conductor limits allow it
the protected bus receives an upstream protection floor equal to the main breaker rating
preview links the main-breaker proposal and bus amperage suggestion when the bus must move with the breaker

The breaker and switch floor and the bus rating floor are intentionally separate settings. Minimum MV/HV Breaker and Switch Rating controls breaker and switch selection above 1 kV; Minimum MV/HV Bus Rating controls auto-sized bus ratings above 1 kV.

The linked bus amperage proposal stays coordinated with the breaker proposal. In Suggest mode, EKX shows the group for review before writing it. In Auto-apply mode, EKX applies the group only if the same server-side coordinated validation passes.

If the protected bus is Manual or Locked, its rating becomes a hard cap. ekx will not silently choose a larger main breaker that exceeds the bus. The sizing result explains whether the optional main-breaker margin was blocked or whether no compliant size exists until the bus or downstream demand changes.

The source-side protected conductor must also be clear. If ekx finds one protected conductor, its ampacity is a hard cap unless that conductor is part of a reviewed coordinated upsize. If there is no conductor because the breaker is proven to connect directly to one source or transformer, ekx sizes from aggregate demand without a conductor cap. A simple one-in/one-out upstream bus does not make the path ambiguous by itself; ekx keeps the nearest breaker-side cable as the protected conductor and uses the upstream bus/cable chain only to prove the source boundary. If the source side is ambiguous, has a branched upstream bus, has multiple possible source paths, or reaches non-source topology before a conductor, ekx blocks the breaker upsize and explains the topology issue.

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
Saving a cable, bus, or transformer sizing margin
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; current selection checks still evaluate it
Locked: the component is frozen for sizing writes; current selection checks still evaluate it

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

CEC 2024 conductor sizing checks whole protected circuits and the declared service-to-load path. The sizing review shows the voltage-drop check even when missing inputs produce no conductor suggestions. Use its Open buttons to find the component needing correction. A complete passing group can include several cables, field-installed bonding conductors and dependent protection changes. Accept the group together. If the installation already passes, Re-size system records that result without changing equipment. See CEC voltage-drop inputs and review.

For a VFD branch, the supply-side voltage-drop check ends at the drive input. With one connected three-phase motor, input current is estimated automatically at full motor load using 95% drive efficiency and 0.90 true input power factor. The voltage-drop calculation assumes 0.98 displacement power factor. An unset motor phase assumes a three-phase output. Review details identify these assumptions; they are estimates, not manufacturer ratings. To use manufacturer data, select the VFD, open Equipment, and override Input current (A) or Input displacement PF. Clear an override to return to Automatic. If the motor demand or connection cannot be resolved, enter the drive input current. The VFD output cable and motor still show a separate unsupported voltage-drop calculation.

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.

For main or aggregate bus protection, linked breaker, bus, and protected-conductor suggestions are applied as one coordinated group. Before writing anything, ekx recomputes the current server-side sizing plan and validates every required member, current value, sizing mode, cable catalog option, and protected-conductor path. If one required member is stale, missing, manual/locked, catalog-invalid, or topology-invalid, none of the group is applied.

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 310.10(G) requirements including the 1/0 AWG minimum for parallel conductors. EKX's six-run ceiling is a product guardrail, not an NEC maximum.

You can configure auto-parallel behavior in the Sizing Rules category of any defaults editor (for example Settings > My 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