Motor Circuit Protector Sizing Chart

There are typically two different sets of protections to design for when designing motor circuits.

Motor circuit protector sizing chart. This is called circuit protection or feeder protection. 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. For motor circuit conductors tapped from a feeder 430 28 determine the ampacity per 430 22. Other means such as overload relays provide the motor overload protection.

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. 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. Typical thermal magnetic circuit. This table is used to size the short circuit protection check the motor data sheets for the motor s full load current.

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 first is to protect the cable supplying the motor the power source and any components upstream on the circuit from the motor. 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.

Locate where your motor falls in table 430 52 based on the full load current and motor size. The table will give you the size of the short circuit protection as a percentage of the full load current. Selecting fuses for motor running protection. The mpcb can interrupt any electrical fault that is.

Motor circuit protectors hmcp eaton s motor circuit protectors are ul recognized instantaneous only breakers for motor short circuit protection. 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. Protection against electrical faults such as short circuits line to ground faults and line to line faults. 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.