Motor Circuit Protector Sizing Chart

Other means such as overload relays provide the motor overload protection.

Motor circuit protector sizing chart. Motor wire size and circuit protection calculator. The table will give you the size of the short circuit protection as a percentage of the full load current. Time delay fuse ratings may be increased to 225 and non time delay fuse ratings to 400 300 if over 600 amperes if the ratings. A motor protection circuit breaker or mpcb is a specialized electromechanical device that can be used with motor circuits of both 60 hz and 50 hz it has several functions that allow it to provide a safe electrical supply for motors.

Locate where your motor falls in table 430 52 based on the full load current and motor size. Circuit breakers which are called mcps or motor circuit protectors are sized with the intent to provide only short circuit and ground fault protection for the motor branch circuit protection per 430 52. When used in tested motor starter combinations they provide complete ul listed motor control and protection and short circuit current ratings up to 100 000a. Short circuit protection the motor branch circuit fuses may be sized as large as shown in table 2 when an overload relay or motor thermal protector is included in the branch circuit.

Protection against electrical faults such as short circuits line to ground faults and line to line faults. This is called circuit protection or feeder protection. Typical thermal magnetic circuit. Selecting fuses for motor running protection.

The first is to protect the cable supplying the motor the power source and any components upstream on the circuit from the motor. A good field reference for maintenance and troubleshooting is ugly s electric motor and controls ugly s electric motors and controls 2014 edition this calculator is based on information found in this reference guide and can help electricians troubleshoot maintenance and control circuits. The next size up protection rule for branch circuits 430 52 c 1 ex 1 doesn t apply to motor feeder short circuit and ground fault protection device sizing. This level of protection requires a well designed true dual element fuse.

The fuse sizing in column 4 for lps rk sp lpn rk sp frs r and frn r fuses provides a degree of motor and circuit overload protection to back up the normal motor overload protective device. For motor circuit conductors tapped from a feeder 430 28 determine the ampacity per 430 22. Motor protection uide using ac motor protection tables to select fuse ratings time delay rk1 and rk5 fuse ratings selected in accordance with the following recommendations also meet nec motor service requirements for motor branch circuit and short circuit protection. This table is used to size the short circuit protection check the motor data sheets for the motor s full load current.