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Gather what exists. Missing one-lines or utility data will stall the study later.
Utility available fault current: request from the serving utility, ideally with X/R ratio3-phase symmetrical short circuit current at the service entrance (kA)
Critical Existing one-line diagram:even if outdated, it reduces field time significantly
Previous arc flash study or short circuit study:useful as a cross-check
Equipment room access schedule:confirm who has keys to every electrical room and substation
Facility voltage levels:confirm whether medium voltage (>1kV) distribution exists
PPE:bring appropriate arc-rated PPE for the voltage levels present
Recorded at the service entrance. If the facility has an on-site generator, document it here too.
Available fault current (kA, 3-phase) at service entranceFrom utility letter or engineering data:do not estimate
Critical Utility X/R ratioIf not provided, use default per IEEE 1584 based on voltage level
Service voltage (V or kV)
Number of utility feeds:single service or redundant
Generator data (if present):kW rating, voltage, power factor, subtransient reactance (X"d)From generator nameplate or spec sheet
Collect for every transformer in the system. Impedance is the most important field:errors here shift fault current across the entire model.
Nameplate data:collect for each transformer
Tag / equipment ID (matches one-line label)
Location (building, room, pad number)
Primary voltage (V or kV)
Critical Secondary voltage (V or kV)
Critical Impedance (%Z)Read directly from nameplate. Do not use a standard value unless nameplate is missing.
Critical X/R ratio (if listed on nameplate)
Winding connection (Delta-Wye, Wye-Wye, Delta-Delta, etc.)
Tap position (if adjustable, note current position)
Photograph nameplate
Photo Collect for every breaker that is a main or feeder device. Branch circuit breakers within a panel are recorded at the panel level.
Identification
Nameplate and frame data
Model and frame designation
Sensor or trip rating (A)
Critical Interrupting rating (kA at rated voltage)
Trip unit settings:electronic trip units only
Long-time pickup (LTP, in multiples of sensor)
Critical Long-time delay (LTD, in seconds or band)
Critical Short-time pickup (STP, in multiples)
Critical Short-time delay (STD, in seconds)
Critical Instantaneous pickup (INT, in multiples, or OFF)
Critical Ground fault settings (if present)
Photograph trip unit faceplate with all dials visible
Photo MV protective devices are relay-operated. Get both the breaker data and the relay settings.
Breaker data
Equipment ID and location
Continuous current rating (A)
Interrupting rating (kA or MVA)
Relay data
Relay manufacturer and model
Overcurrent pickup setting (amps secondary or multiples)
Critical Time dial setting
Critical Instantaneous pickup (if enabled)
Critical Curve type (very inverse, extremely inverse, etc.)
Photograph relay faceplate and settings display
Photo Fuse type and manufacturer significantly affect clearing time. "600A fuse" is not enough information.
Equipment ID and location
Type and class (Class J, Class R, Class L, current-limiting, etc.)
Critical Speed designation (fast, standard, slow, time-delay)
Photograph fuse label or cartridge
Photo Collect for all significant feeders. Branch circuits within a panel can often use standard assumptions. Cable length is frequently estimated:measure when possible.
Source and destination (from Panel A to MCC-1)
Conductor size (AWG or kcmil)
Critical Conductor material (copper or aluminum)
Critical Number of conductors per phase
Insulation type and voltage rating (THWN, XHHW, 600V, 15kV, etc.)
One-way length (feet or meters)Measure or estimate from cable tray runs and conduit routing
Installation method (conduit, cable tray, direct buried)
Document the lineup as a whole, then list each section and its protective device.
Equipment-level data
Short-circuit rating (kA)
Per section / compartment
Section ID and load description
Protective device type (breaker or fuse) and rating
Breaker or fuse settings (per LV breaker or fuse sections above)
Photograph nameplate and directory
Photo Collect one record per panel. Branch circuit detail matters for panels that feed downstream equipment included in the study.
Voltage and phase/wire configuration (120/208V 3P4W, 277/480V 3P4W, etc.)
Main device:type, manufacturer, and rating (or "main lugs only")
Critical Circuit directory:circuit number, breaker size, load description
Photograph nameplate and directory card
Photo Large motors contribute fault current during the first few cycles after a fault. Only motors above a threshold set by the engineer need to be individually modeled.
Motor tag and description
NEMA code letter (for locked rotor kVA)
Photograph nameplate
Photo Do this at the end of the walkdown, not as a separate trip. Discrepancies found in the field are far cheaper to resolve than discrepancies found after the model is built.
All equipment on one-line confirmed to exist in field
Undocumented equipment found and noted
Equipment tags match one-line labels
Tie breakers and alternate sources documented
All discrepancies photographed and noted for engineer
Photo This checklist is provided for general reference only. 70Ez makes no warranties regarding its accuracy, completeness, or suitability for any specific application. It does not constitute engineering advice. Always engage a licensed professional engineer for arc flash studies and electrical safety work. Use of this document is at your own risk.