Interpret the Two-Cycle Parameter as a Limit
Table 130.7(C)(15)(A)(b) identifies a maximum clearing time of 2 cycles, shown as 0.03 seconds, for the referenced Category 1 and Category 2 PPE entries. Treat this value as an equipment-parameter boundary, not as evidence that the protective device must be a fuse.
The available evidence does not restrict the entries to fuse protection. A molded-case circuit breaker can satisfy the boundary if its documented clearing time under the applicable fault condition does not exceed 2 cycles.
Evaluate Breaker Size and Interruption Method
Small molded-case circuit breakers, described in the evidence as generally under 100 A, may operate in 1–2 cycles. Larger frame sizes can require 3–5 cycles because physical contact movement becomes limiting. Older breakers and some higher-voltage SF6 breakers may require 10–12 cycles.
| Device or condition | Clearing or opening time stated in evidence | Decision relative to 2-cycle limit |
|---|---|---|
| Small molded-case breaker, generally under 100 A | Typically 1–2 cycles | Potentially within the limit; verify the installed device |
| Larger-frame breaker | 3–5 cycles | Outside the limit if the applicable clearing time exceeds 2 cycles |
| Older breaker or some higher-voltage SF6 breakers | Up to 10–12 cycles | Outside the 2-cycle limit |
| Vacuum interrupter | Typical specifications list 3 cycles for opening time | Do not assume compliance with a 2-cycle maximum |
Distinguish Opening Time from Total Clearing Time
The vacuum-interrupter discussion identifies 3 cycles as an opening-time specification: the contacts move approximately 1/4 to 3/8 inch, and the arc clears after separation at the next current-zero crossing. Because the table parameter is described as maximum clearing time, do not substitute an opening-time value without confirming that both terms represent the same interval in the device documentation.
The evidence does not provide a breaker model, trip setting, fault current, or time-current curve. It therefore cannot establish compliance for a specific installation.
Verify the Installed Protective Device
- Identify the actual fuse or circuit breaker and its frame size; do not infer the device type from the PPE category.
- Obtain the manufacturer's applicable clearing-time data for the installed configuration and fault condition.
- Confirm whether the published value is opening time or total clearing time.
- Compare the applicable clearing time directly with the 2-cycle, 0.03-second maximum. If it exceeds that boundary or cannot be established, do not apply the table entry on the assumption that the breaker behaves like a fuse.
FAQ
Does the 2-cycle clearing-time limit apply only to fuses?
No such restriction appears in the supplied evidence. A molded-case circuit breaker may meet the parameter when its documented clearing time is no more than 2 cycles.
Can a molded-case circuit breaker clear a fault in 2 cycles?
Small molded-case breakers, generally under 100 A in the evidence, are described as typically operating in 1–2 cycles. Verify the actual breaker and applicable fault condition rather than relying on that general range.
Can I use a 3-cycle breaker with a 2-cycle table limit?
Not on the basis of the supplied timing alone. A documented 3-cycle value exceeds the stated 2-cycle maximum, and an opening-time rating must not be treated as total clearing time without confirmation.