Does an air compressor require a disconnect?
Yes in most installations. An air compressor is a motor load, so Article 430 applies. NEC 430.102(B) requires a disconnecting means in sight from the motor location and the driven machinery. For a hardwired shop compressor, that means a disconnect at the compressor you can see from the machine, not just the breaker across the building.
Cord-and-plug compressors
For a cord-connected compressor, 430.109(F) allows the attachment plug and receptacle to serve as the disconnecting means. That covers the typical garage 120 volt or 240 volt portable unit: unplug it and it is disconnected. The receptacle needs to be accessible, and on 2023 code in a dwelling garage it needs GFCI protection under 210.8(A) regardless of voltage up to 250 volts.
Hardwired units: what qualifies
The disconnect must open all ungrounded conductors, be readily accessible, and per 430.109 can be a motor circuit switch rated in horsepower, a molded case circuit breaker, a molded case switch, or for smaller motors other listed means. It must have an ampere rating at least 115 percent of the motor full load current per 430.110. A horsepower-rated safety switch next to the compressor is the standard answer. The within sight rule means visible and within 50 feet per Article 100.
The lockable breaker exception
430.102(B) Exception allows the branch circuit disconnect to serve as the motor disconnect without being within sight where it is capable of being locked in the open position, with a permanently installed locking provision, but the exception is limited to installations where locating the disconnect at the machine is impracticable or introduces hazards, and to some industrial setups with written procedures. For an ordinary shop compressor, plan on the local disconnect; most inspectors read the exception narrowly.
Field notes
Size the branch circuit from Table 430.248 or 430.250 full load currents, not the nameplate amps, take 125 percent for the conductors per 430.22, and remember the motor's pressure switch is a controller, not a disconnect. A 5 hp 240 volt single phase compressor is 28 FLC, 35 amp conductors, and commonly a 50 amp breaker under 430.52. Put the disconnect where a tech bleeding the tank or changing a pressure switch can kill power without walking away from the machine.