This is called circuit protection or feeder protection.
Motor circuit protector sizing chart.
Motor wire size and circuit protection calculator.
The mpcb can interrupt any electrical fault that is.
Protection against electrical faults such as short circuits line to ground faults and line to line faults.
Typical thermal magnetic circuit.
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.
There are typically two different sets of protections to design for when designing motor circuits.
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.
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.
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.
Selecting fuses for motor running protection.
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.
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.
Motor circuit protectors hmcp eaton s motor circuit protectors are ul recognized instantaneous only breakers for motor short circuit protection.
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.
Other means such as overload relays provide the motor overload protection.
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.
Locate where your motor falls in table 430 52 based on the full load current and motor size.
This table is used to size the short circuit protection check the motor data sheets for the motor s full load current.
For motor circuit conductors tapped from a feeder 430 28 determine the ampacity per 430 22.
This level of protection requires a well designed true dual element fuse.
