What is the purpose of a coordination study, and does your facility need one?
It stops a fault on one feeder from blacking out the rest of the plant. For emergency and standby circuits, the NEC makes that a requirement.
Does your facility need a coordination study now?
Two answers you already know. Your verdict appears here, with the clause cited. No email needed.
Free · instant · based on NFPA 70B-2023 and NEC 2023 700.32
Trusted by the World’s Most Demanding Plants.
Which NEC articles require selective coordination?
Four instruments carry the requirement. Three articles of the NEC (NFPA 70) make selective coordination mandatory for named systems. NFPA 70B makes the coordination study part of the maintenance program for every facility that adopts it.
| Instrument | Clause | What it requires | Interval |
|---|---|---|---|
| NEC (NFPA 70) 2023 | 700.32 | Emergency system overcurrent devices selectively coordinated with all supply-side and load-side devices. The selection is made by a licensed professional engineer or other qualified person, documented, and made available to those who design, install, inspect, maintain and operate the system. | At design, and re-evaluated when devices or the system change |
| NEC 2023 | 701.32 | The same selective coordination duty for legally required standby systems. | At design, and on change |
| NEC 2023 | 708.54 · 620.62 | Critical operations power systems, and elevator feeders where one feeder supplies more than one driving machine. | At design, and on change |
| NFPA 70B-2023 | Ch. 6 (6.4) | Coordination studies as part of the electrical maintenance program, kept current with the short-circuit and incident energy studies. | 5 years maximum |
Editions matter. NEC adoption is decided state by state, so a site may be enforced to an earlier edition than 2023. Name the edition your jurisdiction enforces in the specification. VB confirms it for every project.
Not sure which NEC edition your state enforces?
When is a coordination study required, beyond the five years?
The five-year interval is the ceiling. Any of these changes the fault currents or clearing times the settings were chosen for, so coordination has to be checked again.
Added a source or replaced devices since your last study?
Who must select and document selective coordination?
NEC 700.32 is specific about who makes the selection and who must be able to see it.
- The licensed engineer or qualified personSelects the overcurrent devices and settings that achieve selective coordination, and documents the selection.
- The authority having jurisdictionMust be able to see the documentation at inspection. The code requires it to be made available.
- The installing contractorInstalls the devices, ratings and trip settings the selection specifies, not a near equivalent.
- The facility ownerKeeps settings as documented, and has coordination re-checked whenever a device or source changes.
How is selective coordination applied in a data center?
In a data center the requirement applies to the emergency and legally required standby paths. Those are also the paths where a coordination failure costs the most.
- Generator and transfer-switch paths that feed life-safety loads are selectively coordinated under NEC 700.32.
- UPS, static transfer switch and PDU breakers carry critical load, so a mis-graded trip at the PDU can drop a whole row.
- Arc energy reduction settings under NEC 240.87 shorten clearing times, so they are checked against coordination rather than set in isolation.
How is a coordination study done, step by step?
VB models every protective device in ETAP or SKM PowerTools. No setting is calculated by hand.
Collect device data
Relay types, trip units, CT ratios and existing settings read at each device during the walkdown.Build the model
Single-line verified against the installed system, with the utility fault level and every source modeled.Run short circuit
Maximum and minimum fault currents at every bus: the limits each device must coordinate within.Plot the curves
Time-current curves plotted for every path from source to load, with overlaps and gaps marked.Set and resolve
Pickup and delay settings chosen. Where a trade-off between speed and selectivity remains, it is stated in writing.Issue and sign
Settings table, curves and report signed by the engineer of record, ready for the inspector.What does a coordination study deliver?
Two artifacts carry the proof: the settings at the device, and the curves that justify them.
The settings table
The time-current curvesWho signs the study?
The study is signed by a named engineer, not by a company. Three roles keep responsibility visible.
Reviewing engineer
Checks the model and the settings basis independently of the modeler.Professional Engineer
A PE licensed in the facility’s state signs the study, as standard practice.Documented selection
The signed settings table is the documentation NEC 700.32 requires to be made available.Illustrative case: one feeder fault, one bus lost
Modeled on a typical finding. A colocation data center in the US Midwest saw its main switchboard breaker trip during a fault on a downstream panel feeder. The study traced it to a replaced feeder breaker installed with factory trip settings.
| What was checked | What was found |
|---|---|
| Feeder breaker settings | Factory defaults after replacement, never re-coordinated |
| Main and feeder curves | Overlapping in the short-time band, so either could trip first |
| Fix | Feeder short-time delay and main pickup reset; selectivity restored on the emergency path |
Send this to the person who owns the shutdown calendar.VB Engineering capability brochure. One file, linked, not attached to this page.
Questions facility engineers ask about coordination studies
What is a relay coordination study?
A relay coordination study sets the pickup and time delay of every protective relay, breaker trip unit and fuse so the device nearest a fault clears it first. It is built on a short-circuit study and delivered as time-current curves and a settings table.
What is the difference between an arc flash study and a coordination study?
A coordination study decides which device trips and how fast. An arc flash study uses those clearing times to calculate incident energy at each piece of equipment. Slow settings chosen for selectivity raise incident energy, so the two studies are best done together.
What is the difference between a short circuit study and a coordination study?
The short circuit study calculates the fault current at every bus. The coordination study uses those currents to set devices so they trip in sequence. Coordination cannot be done without the short circuit results.
What is a TCC curve?
A time-current curve plots how long a protective device takes to trip at each level of current. Overlaying the curves of devices in series shows whether the downstream device clears first, and by what margin.
How often must a coordination study be updated?
NFPA 70B-2023 calls for coordination studies to be reviewed at intervals of no more than five years, and sooner when devices, sources or the utility supply change.
Is NFPA 70B mandatory?
Since its 2023 edition NFPA 70B is a standard written in mandatory language, not a recommended practice. Authorities, insurers and client specifications that adopt it hold facilities to its maintenance and study requirements.
What is selective coordination?
Selective coordination is the NEC term for localizing an overcurrent condition to the circuit or equipment affected. It is achieved by choosing overcurrent devices, ratings and settings so that only the device nearest the fault opens, across the full range of fault currents.
Which systems must be selectively coordinated?
NEC 700.32, 701.32 and 708.54 require it on emergency, legally required standby and critical operations power systems, and 620.62 on elevator feeders. Many owners extend it to the whole distribution because a nuisance trip anywhere costs production.
Who can perform a coordination study?
NEC 700.32 assigns the selection to a licensed professional engineer or other qualified person engaged primarily in the design, installation or maintenance of electrical systems. VB studies are signed by a PE licensed in the facility’s state.
Is type 1 or type 2 coordination the same thing?
No. Type 1 and type 2 describe how a motor starter must withstand a short circuit under IEC 60947-4-1. Selective coordination is about which upstream or downstream device trips first.
How does NEC 240.87 arc energy reduction affect coordination?
NEC 240.87 requires an arc energy reduction method on breakers that can be set to 1,200 A or more, such as a maintenance switch or differential relaying. Those faster settings are checked against coordination so they do not trip the wrong device.
When is a coordination study required in Texas or California?
Both states enforce the NEC through state adoption, so the selective coordination articles apply to emergency, standby and critical operations systems there. Confirm the NEC edition your jurisdiction enforces before the study is specified.
Question not answered here? That is usually the one worth asking.
Where to go once you know you need a study
These pages answer the next questions: what the study includes, what it costs, and how it fits the other studies.
Scope, cost and duration
What a relay coordination study includes, how long it takes and how it is priced.
The inputShort circuit study
The fault currents every coordination setting depends on.
Done togetherArc flash study
How coordination settings drive incident energy, and what the study costs.
RenewablesSolar and BESS
Protection coordination when inverter sources supply little fault current.
Send us the year of your last study
Tell us when your coordination study was last done and what has changed since. We reply in writing with where you stand and what to do next.
- We confirm whether coordination is current against the interval and the change triggers
- We name the NEC edition your state enforces, not the newest published
- You get the answer in writing whether or not you invite us to bid
Confirm where you stand
- A written answer from a power system engineer, not a sales desk
- Your position checked against NEC 700.32 and NFPA 70B-2023
- The NEC edition your state enforces, named
Prefer to write? connect@groupvb.com · or WhatsApp us from the chat button