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HOW TO CHOOSE PPE
Select the type of AC equipment:
Panelboards or other equipment rated 240 volts and belowPanelboards or other equipment rated greater than 240 volts and up to 600 volts600-volt class motor control centers (MCCs)Maximum of 65 kA available fault current600-volt class motor control centers (MCCs)
Maximum of 42 kA available fault current600-volt class switchgear
(with power circuit breakers or fused switches)
and 600-volt class switchboardsOther 600-volt class equipment
(277 volts through 600 volts, nominal) NEMA E2 (fused contactor) motor starters,
2.3 kV through 7.2 kVMetal-clad switchgear, 1 kV through 15 kVArc-resistant switchgear 1 kV through 15 kV
[for clearing times of less than 0.5 sec (30 cycles) with an available fault current not to exceed the arc-resistant rating of the equipment], and metal-enclosed interrupter switchgear, fused or unfused of arc-resistant-type construction,
1 kV through 15 kVOther equipment 1 kV through 15 kV
Note: For equipment rated 600 volts and below and protected by upstream current-limiting fuses or current-limiting circuit breakers sized at 200 amperes or less, the arc flash PPE category can be reduced by one number but not below arc flash PPE category 1.
Informational Note to NFPA 70E Table 130.7(C)(15)(a): The following are typical fault clearing times of overcurrent protective devices:
- 0.5 cycle fault clearing time is typical for current limiting fuses when the fault current is within the current limiting range.
- 1.5 cycle fault clearing time is typical for molded case circuit breakers rated less than 1000 volts with an instantaneous integral trip.
- 3.0 cycle fault clearing time is typical for insulated case circuit breakers rated less than 1000 volts with an instantaneous integral trip or relay operated trip.
- 5.0 cycle fault clearing time is typical for relay operated circuit breakers rated 1 kV to 35 kV when the relay operates in the instantaneous range (i.e., "no intentional delay").
- 20 cycle fault clearing time is typical for low-voltage power and insulated case circuit breakers with a short time fault clearing delay for motor inrush.
- 30 cycle fault clearing time is typical for low-voltage power and insulated case circuit breakers with a short time fault clearing delay without instantaneous trip.
Informational Note No. 1: See Table 1 of IEEE 1584TM, Guide for Performing Arc Flash Hazard Calculations, for further information regarding Notes b through d.
Informational Note No. 2: An example of a standard that provides information for arc-resistant switchgear referred to in Table 130.7(C)(15)(a) is IEEE C37.20.7, Guide for Testing Metal-Enclosed Switchgear Rated Up to 38 kV for Internal Arcing Faults.
All notes are from 2018 edition of NFPA 70E Table 130.7(C)(15)(a): Arc-flash PPE Categories for Alternating Current (ac) Systems.
