Introduction: More Than Just Wires and Breakers
When most people think of an electrical system, they picture wires, panels, and switches. But for engineers and facility managers, the real challenge is ensuring that the system behaves safely and reliably under all conditions. That’s where system analysis comes in.
Fortunately, you don’t need to be a mathematician or run advanced modeling software to understand the big picture. Here’s what facility managers need to know about short-circuit currents, coordination, and voltage drop — the three pillars of system analysis.
Short-Circuit Current: Planning for the Worst
A short circuit is when electricity takes an unintended path — often with devastating consequences.
- Why it matters: Fault currents can be 10 to 20 times higher than normal operating currents.
- The risk: If equipment isn’t rated to handle those currents, breakers can fail, gear can explode, and safety is compromised.
- Facility manager’s role:
- Ensure switchgear and breakers have ratings that match the available fault current.
- Update fault current studies whenever utility service or system configuration changes.
Example: A data center upgrading to larger utility transformers suddenly faces much higher fault current. If breakers aren’t upgraded too, the system may no longer be safe.
Coordination: Making Sure the Right Device Trips
Selective coordination ensures that only the breaker nearest the fault opens, leaving the rest of the system running.
- Why it matters: Without coordination, a fault in one lab hood could trip a feeder breaker — shutting down an entire science building.
- Tools: Engineers use time-current curves (TCCs) to align settings so downstream devices trip first.
- Facility manager’s role:
- Ask vendors and engineers for coordination studies.
- Require compliance with NEC 700 and NEC 517 for emergency and healthcare systems.
- Keep one-line diagrams and breaker settings updated.
Example: Hospitals are legally required to maintain selective coordination so a fault in a non-critical outlet doesn’t black out operating rooms.
Voltage Drop: Keeping Equipment Healthy
Electricity isn’t free of losses — voltage drops as it travels through wires.
- Why it matters: Too much voltage drop reduces equipment performance, overheats motors, and can damage sensitive electronics.
- Typical limits: NEC recommends no more than 3% drop on feeders and 5% total from source to load.
- Facility manager’s role:
- Pay attention to long cable runs (like parking lot lighting or remote buildings).
- Work with engineers to size conductors appropriately.
- Monitor PQ (power quality) to catch undervoltage conditions early.
Example: An MRI machine starved of proper voltage may malfunction, requiring costly service calls and risking patient care.
The Facility Manager’s Toolkit
While the math behind these studies is handled by engineers using software like ETAP or SKM, facility managers don’t need to crunch numbers. What matters is:
- Asking the right questions:
- “Is our gear rated for available fault current?”
- “Do we have selective coordination on emergency circuits?”
- “Are we monitoring voltage drops or PQ issues?”
- Keeping documentation current: One-line diagrams, breaker settings, and study reports.
- Using monitoring platforms: Systems like NovaVue provide real-time alarms and historical reports, ensuring problems are caught before they become outages.
Final Thoughts
System analysis isn’t about equations — it’s about protecting people, ensuring uptime, and avoiding expensive failures. By understanding the basics of short-circuit current, coordination, and voltage drop, facility managers can bridge the gap between technical studies and operational decision-making.
With NovaVue, these insights become even more accessible, as the platform automatically collects, organizes, and reports on the data needed to validate safety, compliance, and efficiency.