Trip Tolerances for Field Testing of Circuit Breakers

Tech Library Technical Notes
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Instantaneous Trip Tolerances for Field Testing of Circuit Breakers

Tolerances of Manufacturer's Published Trip Range
Circuit Breaker Type Tolerance of Settings High Side Low Side
Electronic Trip Unit (1) +30% / -30% ---- ----
Adjustable (1) +40% / -30% ---- ----
Nonadjustable (2) ---- +25% -25%

Notes:

  1. Tolerances are based on variations from the nominal settings.
  2. Tolerances are based on variations from the manufacturer's published trip band (i.e., -25% below the low side of the band; +25% above the high side of the band).

References: NEMA publication AB4, Table 4. ANSI/NETA-ATS 2013 Table 100.8.

Inverse Time Trip Test at 300% of Rated Continuous Current of Circuit Breakers Molded-Case Circuit Breakers

Range of Rated Continuous Current (Amperes) Maximum Trip Time in Seconds For Each Maximum Frame Rating (1)
≤ 250V 251 - 600V
0-30 50 70
31-50 80 100
51-100 140 160
101-150 200 250
151-225 230 275
226-400 300 350
401-600 ---- 450
601-800 ---- 500
801-1000 ---- 600
1001-1200 ---- 700
1201-1600 ---- 775
1601-2000 ---- 800
2001-2500 ---- 850
2501-5000 ---- 900
6000 ---- 1000

Notes

  1. Trip times may be substantially longer for integrally-fused circuit breakers if tested with the fuses replaced by solid links (shorting bars).

References: NEMA Standard AB 4-1996: Guidelines for Inspection and Preventive Maintenance of Molded-Case Circuit Breakers Used in Commercial and Industrial Applications, Table 5-3. ANSI/NETA ATS-2013 Table 100.7