Short-Circuit and Protective Device Coordination Studies

Matthew Lohens

Oct 11

3 min read

By Matt Lohens, P.E., MHL Consulting PLLC. Last reviewed: October 2026

Short answer: A short-circuit study finds the maximum fault current at every point in your electrical system and checks that each breaker, fuse and switchboard can safely interrupt or withstand it. A coordination study sets protective devices so that only the device closest to a fault opens, instead of tripping a main and shutting down the whole facility. Together with an arc flash study they form a complete power system study. MHL Consulting performs and stamps these studies as a licensed Professional Engineer in AZ, CA, HI, IL, NV, OR, PA, TX, UT and VA.

What does a short-circuit study tell me?

It answers one question: if a fault happens here, how much current flows, and can the equipment handle it? NEC 110.9 requires equipment to have an interrupting rating at least equal to the available fault current, and 110.10 requires protective devices and component ratings to be selected so a fault will not damage the equipment. The study, which we run in SKM PowerTools, starts with the utility's available fault current and adds transformer impedance, cable impedance and motor or generator contribution at each bus. It flags any equipment whose rating is too low, which matters most after a utility upgrade, a new transformer or a generator addition.

What does a coordination study do?

It plots the time-current curves of upstream and downstream protective devices on one chart and checks that they do not overlap in the fault range that matters. The result is a set of recommended settings and, where the existing devices cannot coordinate, a list of device changes.

The NEC requires selective coordination in specific cases, including emergency systems (700.32), legally required standby systems (701.32), critical operations power systems (708.54) and elevator circuits (620.62). Check which NEC edition your jurisdiction has adopted, and note that healthcare facilities have additional requirements.

When do I need these studies?

A new or upgraded service, transformer or switchgear
Adding a generator, transfer switch or large motor
A utility change that raises available fault current
Selective coordination is required for emergency or standby systems
Insurance, lender or owner requirements, or buying a facility
Service equipment where the NEC requires the maximum available fault current to be field marked (110.24)
Large breakers: NEC 240.87 requires an arc energy reduction method for breakers rated or adjustable to 1,200 amps or more, which is easier to document with a coordination study in hand

What do I need to send to start?

One-line diagram, or permission for a site walk to build one
The utility's available fault current and transformer data
Breaker, fuse and relay manufacturer, model and settings
Cable sizes, lengths and conductor material
Motor, generator and UPS ratings

What do I receive?

Short-circuit results at each bus, with equipment ratings checked against them
Time-current curves for each coordinated path
Recommended device settings and any device replacements needed
An updated one-line diagram
A report sealed by a licensed PE

FAQ

What is the difference between coordination and selective coordination? Coordination in a general study aims to minimize the outage when a fault occurs. Selective coordination is the stricter code term: for the covered systems, only the nearest device may open for the full range of overcurrent.

Can I coordinate my system with molded-case breakers only? Often not at high fault currents. Selective coordination may need fuses, breakers with adjustable short-time delay, or zone-selective interlocking, which is what the study determines.

Do I need all three studies? Not always, but they share the same data, so doing the short-circuit, coordination and arc flash studies together avoids collecting the data twice and keeps the results consistent.

Which states do you work in? We are licensed in AZ, CA, HI, IL, NV, OR, PA, TX, UT and VA.

Next step

Send us your one-line diagram and a short description of the facility, or book a 15-minute call. We will tell you which studies you need and what data to gather. We take on facilities of any size and voltage class.