Short-Circuit Study
Remake batch 25 and its neighbor re-points, batch 24 where missing, and the adopted-electrical-code parameter: brought in line with the authoring repository
Showing changes from Rev 9
to Rev 10
in Short-Circuit Study.
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title: Short-Circuit Study
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When to use: The short-circuit study for a project's electrical power distribution system, from the utility point of delivery through every point at which an interrupting rating, a close-and-latch rating, a short-time withstand rating, a bus bracing rating, or a marked short-circuit current rating is confirmed, on AC systems rated 1000 V and below through 38 kV with utility, generator, inverter-based, and paralleled sources. Covers who performs the study and when it is delivered, the calculation method and the duty networks, the fault types and the maximum and minimum cases, the system model and the data it is built from (the utility's available fault current and X/R, transformer impedances, conductor impedances and lengths, motor and generator contribution, inverter-based sources, and the survey of existing equipment on a renovation), the source operating cases, the equipment duty evaluation, the treatment of series-rated combinations, the available fault current and date that NFPA 70 110.24 requires at the service equipment, the report and the model handed to the coordination and arc-flash studies, and the events that call for a re-study.
− Not intended for: the time-current coordination of the protective devices and their settings ([[sync/protective-coordination-study]]); the incident energy and arc-flash boundary at each piece of equipment ([[sync/arc-flash-study]]); the field acceptance program applied to the installed equipment before energization ([[sync/electrical-acceptance-testing]]); the label on which the available fault current is marked, which the project's identification standard governs ([[sync/electrical-identification]]); the grounding electrode system and the bonding that forms the ground-fault return path ([[sync/grounding-and-bonding]]); the short-circuit current rating determination of an industrial control panel under UL 508A Supplement SB ([[sync/industrial-control-panels]]); load-flow, voltage-drop, motor-starting, harmonic, and transient-stability studies; DC system fault calculations; and fault calculations on the utility's side of the point of delivery.
+ Not intended for: the time-current coordination of the protective devices and their settings ([[sync/protective-coordination-study]]); the incident energy and arc-flash boundary at each piece of equipment ([[sync/arc-flash-study]]); the field acceptance program applied to the installed equipment before energization ([[sync/electrical-acceptance-testing]]); the label at the service equipment on which this study's result is marked, as a product ([[sync/equipment-labeling]]); the grounding electrode system and the bonding that forms the ground-fault return path ([[sync/grounding-and-bonding]]); the short-circuit current rating determination of an industrial control panel under UL 508A Supplement SB ([[sync/industrial-control-panels]]); load-flow, voltage-drop, motor-starting, harmonic, and transient-stability studies; DC system fault calculations; and fault calculations on the utility's side of the point of delivery.
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- the ratings the equipment is ordered to, which each equipment standard carries in its own datasheet and this study confirms, under [[sync/low-voltage-switchgear]], [[sync/medium-voltage-switchgear]], [[sync/low-voltage-switchboards]], [[sync/panelboards]], [[sync/motor-control-centers]], [[sync/busway]], [[sync/automatic-transfer-switches]], [[sync/generator-paralleling-switchgear]], [[sync/secondary-unit-substations]], and the other equipment standards that name this study
- the utility point of delivery and the rules that apply at the service, under [[sync/electrical-service-entrance]], the service conductors, under [[sync/distribution-feeder-cables]], and the service equipment as products, under [[sync/low-voltage-switchboards]], [[sync/low-voltage-switchgear]], [[sync/enclosed-switches-and-disconnects]], and [[sync/panelboards]]
−- the available fault current label at the service equipment, as a product, under the project's identification standard (see [[sync/electrical-identification]]); this study supplies the value and the date that go on it
+- the label at the service equipment, as a product, under the project's identification standard (see [[sync/equipment-labeling]]); this study supplies the available fault current value and the date that go on it
- the grounding electrode system, the bonding, and the system grounding method of each source, under [[sync/grounding-and-bonding]]; this study models the grounding method the one-line diagram shows and calculates the ground-fault current that results
- the short-circuit current rating determination of an industrial control panel, under [[sync/industrial-control-panels]]; this study compares the marked rating with the available fault current at the panel
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### The value stated for the field marking shall be the maximum-case three-phase symmetrical current calculated under this standard at the line terminals of the service equipment, with the utility's value and the growth margin shown separately in the record.
−### The field marking itself, its material, its format, and its placement on the service equipment, shall be as the project's identification standard requires (see [[sync/electrical-identification]]), and the Contractor shall apply the value and the date this study states and no other.
+### The field marking itself, its material, its format, and its placement on the service equipment, shall be as the project's identification standard requires (see [[sync/equipment-labeling]]), and the Contractor shall apply the value and the date this study states and no other.
### The calculation behind the marking shall be kept available to those who design, install, inspect, maintain, or operate the system, as NFPA 70 110.24(A) requires, and the closeout submittal of the record and the native model is how this standard meets that requirement.
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### The fault current at a bus is a property of everything upstream of it, and most of the events that change it are ordinary maintenance: a transformer swapped for the one in stock, a breaker replaced with another make, a feeder re-pulled on a different route. None of them look like a reason to commission a study, which is why the list is written for the operations staff in the words of the work they do rather than in the terms of the calculation. {note}