This NFPA 110 Type 10 system's generator actually takes 11.8 seconds to be ready — 1.8 seconds over its own Type 10 target — but the UPS bridge easily covers the gap.
| Target maximum interruption | 10 seconds (defines NFPA Type 10) |
| Minimum runtime requirement | 48 hours (defines NFPA Class 48) |
| ATS start delay | 1.5 s |
| Genset crank-to-rated time | 10 s |
| ATS transfer time | 0.3 s |
| UPS autonomy (battery ride-through) | 30 s |
| Generator rated output | 500 kW |
| Load steps | 50 kW emergency @5s, 80 kW legally-required @10s, 150 kW optional @15s |
The bridge check requires the UPS autonomy to exceed the genset-ready time by a 25% safety margin, not just barely cover it.
| Time | Load step | Priority | Cumulative | % of rated |
|---|---|---|---|---|
| 5 s | +50 kW Life-Safety Lighting | Emergency | 50.0 kW | 10% |
| 10 s | +80 kW Load 2 | Legally-Required | 130.0 kW | 26% |
| 15 s | +150 kW Load 3 | Optional | 280.0 kW | 56% |
| Check | Requirement | Actual | Status |
|---|---|---|---|
| Generator alone meets Type 10 target | gensetReadyS ≤ 10 s | 11.8 s | ✗ FAIL |
| UPS bridge covers the gap with 25% margin | UPS autonomy ≥ 14.75 s | 30 s | ✓ PASS |
| Staged load pickup sequence | Priority order correct, no overload | No warnings | ✓ PASS |
Key insight: A generator's crank-to-rated time is a real physical characteristic of the machine, not something a specification can simply overrule — when an NFPA Type rating demands a faster restoration time than the generator alone can deliver, a UPS bridge (or a faster-starting generator) is a genuine engineering necessity, not a redundant nice-to-have. This calculator's separate 'genset alone vs. Type target' and 'does the UPS bridge cover the gap' checks are what surface a mismatch like this before it becomes a real-world life-safety gap.
Every input in this example is editable in the live calculator — free, no signup.
Open Emergency Power (Genset+UPS) calculator →Real generator starting times vary run to run (battery condition, ambient temperature, fuel system priming, and simple mechanical variability all affect actual crank time), so a bridge system sized with zero margin against a single nominal genset-ready time could fail on a day when the generator happens to start slightly slower than usual — the 25% margin exists specifically to absorb that real-world variability.
NFPA 110 Chapter 6.3 requires higher-priority loads (Emergency, NEC 700) to be restored before lower-priority loads (Legally-Required Standby, then Optional Standby) — the calculator specifically flags a warning if a lower-priority step is scheduled to pick up before a higher-priority one, since that would mean life-safety loads are waiting behind less critical loads for power restoration, which is a genuine code violation, not just a scheduling inefficiency.