Quick Hits

Episode 3: Overload & Short-Circuit/Ground-Fault Protection (Parts III & IV)

SLIDE 2 (MOTOR OVERLOAD PROTECTION)

Protecting Against Overheating:

• Continuous Duty Sizing (430.32): Motors with a service factor of 1.4 or greater or a temperature rise of 40°C or less must have overloads sized at no more than 125% of the motor nameplate current rating. All other motors are capped at 115%.

• Purpose: Overload devices protect motor windings, control apparatus, and branch-circuit conductors against excessive heating due to overloads or failure to start.

SLIDE 3 (BRANCH-CIRCUIT SHORT-CIRCUIT & GROUND-FAULT PROTECTION)

Handling Fault Currents (430.52):

• Device Sizing (Table 430.52): Branch-circuit short-circuit and ground-fault protective devices must be capable of carrying the starting current of the motor. Inverse-time circuit breakers are typically permitted up to 250% (and up to 400% for specific designs) of the motor FLC.

• Maximum Rating: If the standard OCPD rating does not correspond to the calculated percentage, the next higher standard size is permitted.

SLIDE 4 (WRAP-UP)

💡 Apprentice Pro-Tip: Remember the golden split: Overloads protect against running overcurrents (thermal/overheating), while Short-Circuit/Ground-Fault OCPDs (breakers/fuses) protect against catastrophic short circuits!

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