A protective device coordination study makes sure your breakers and fuses trip in the right order. When a fault occurs, the device closest to it should clear first, isolating the problem to the smallest possible part of the system. When coordination is wrong, a fault on one branch circuit takes out the main and drops the whole building.
The analysis is done on time current curve (TCC) plots, where each protective device's operating characteristic is drawn against every other device in the path back to the utility. Where curves overlap, devices can operate together and selectivity is lost.
What coordination buys you
- Uptime. A fault in one area stops one area, not the plant.
- Faster troubleshooting. The device that opened tells you where the problem is.
- Lower incident energy. Coordination settings directly control clearing time, and clearing time drives incident energy. Most arc flash mitigation is done here, in the settings, before anyone spends money on equipment.
- Equipment protection. Devices that clear promptly limit let-through energy and mechanical stress.
Coordination and arc flash mitigation pull against each other. Longer time delays improve selectivity; they also increase incident energy, because incident energy is a function of how long the arc burns. Resolving that tension is engineering judgment, not a software output, and it is where a coordination study earns its cost.
Every panel belongs in the TCCs
This is the question to ask any firm quoting you a coordination study. Each panel should appear in the time current curve plots. Studies that only plot main switchgear and assume the branch panels have not evaluated coordination — they have evaluated part of it, and the part they skipped is usually where the miscoordination lives.
Deliverables
- Time current curve plots for every device path, branch panels included
- Recommended settings for every adjustable protective device, in a table your electrician can work from
- Identification of miscoordinated devices, with what it would take to fix each
- Arc flash impact of the recommended settings, so the two studies agree
- Report sealed by a California licensed Professional Engineer
On new construction, Division 26 05 73 requires the protective device coordination study alongside the arc flash study, completed before equipment is ordered so that final ratings and device selections reflect the analysis.
Talk to the engineer who does the work
No sales team. You speak directly with a California licensed Professional Engineer about your equipment, your schedule, and what the study will actually cost.