Coordination Studies
Time-current coordination to ensure protective devices clear faults quickly while minimizing unnecessary outages and nuisance trips.
Protection that is too slow can damage equipment; protection that is too aggressive can take down large portions of the facility. Coordination studies help find the right balance.
What Is A Coordination Study?
A coordination study examines how breakers, fuses, and relays operate together during overcurrent and short circuit events. We develop time-current curves (TCCs) that plot:
- Protective device pickup, time delay, and instantaneous regions
- Expected fault currents at various points
- Interactions between upstream and downstream devices
The goal is for the closest device to the fault to operate first, while upstream devices remain closed, whenever practical.
Why Coordination Matters
Selective coordination:
- Limits the extent of outages during faults
- Reduces the probability of tripping main devices for local problems
- Helps protect sensitive loads and critical operations
- Supports selective coordination requirements where applicable
- Provides a documented basis for protective settings
Our Process
1. Collect device data and existing settings
2. Build the protective device model in the study software
3. Plot short circuit levels and protective device curves on TCCs
4. Adjust settings to improve selectivity while maintaining adequate protection
5. Document recommended settings and any limitations or constraints
6. Coordinate with your team and, where needed, your utility or generator vendor
What We Deliver
- Time-current curves for key feeders and branches
- Recommended breaker and relay settings, including long-time, short-time, instantaneous, and ground fault elements where applicable
- Notes on selective coordination and any necessary trade-offs
- Settings sheets that maintenance staff can use for implementation and verification
What We Need From You
- Existing protective device settings, if available
- One-line diagrams and protective device schedules
- Operational priorities (for example, which loads must never trip with others)
- Any existing selective coordination requirements from codes or standards
Codes And Standards
- NEC selective coordination requirements for emergency, legally required standby, and critical branches where applicable
- NFPA 99 and NFPA 110 for certain healthcare and generator systems
- Utility interconnection or relay coordination requirements for medium-voltage systems
FAQs
Q: Do we have to change all our settings?
Not necessarily. We often retain settings that are already performing well and focus on devices where better coordination or protection is possible.
Q: Can you review an existing coordination study?
Yes. We can audit prior work, verify assumptions, and update curves and settings as the system changes.