Motor Circuit Protection

General Information

The parameters to be considered for motor-feeder protection depend on:

the application (type of machine driven, operating safety, frequency of operation, etc.)
the level of continuity of service required by the load or the application
the applicable standards for the protection of equipment.

The required electrical functions are:

isolation
switching, generally at high endurance levels
protection against overloads and short-circuits, adapted to the motor
additional special protection.

A motor branch circuit must comply with the requirements of standard UL 508 concerning contactors and their protection:

coordination of feeder components
overload relay trip classes.

Motor Branch Circuit Protection Function

A motor branch circuit comprises a set of devices for motor protection and control, as well as for protection of the branch circuit itself.

Switching

The purpose is to control the motor (ON / OFF), either manually, automatically or remotely, taking into account overloads upon start-up and the long service life required. This function is provided by a contactor. When the coil of the contactor's electromagnet is energized, the contactor closes and establishes, through the poles, the circuit between the upstream supply and the motor, through the circuit breaker.

Basic Protection

Short-circuit protection
Detection and breaking, as quickly as possible, of high short-circuit currents to avoid damage to the installation. This function is provided by a circuit breaker.
Overload protection
Detection of overload currents and motor shutdown before temperature rise in the motor and conductors damages insulation. This function is provided by a circuit breaker or a separate motor overload relay.
Phase unbalance or phase loss protection
Phase unbalance or phase loss can cause temperature rise and braking torques that can lead to premature aging of the motor. These effects are even greater during starting, therefore protection must be virtually immediate.

Additional Electronic Protection

Locked rotor
Under-load
Long starts and stalled rotor
Insulation faults

Trip Class of an Overload Relay Device

The motor branch circuit includes thermal protection that may be built into the circuit breaker. The protection must have a trip class suited to motor starting. Depending on the application, the motor starting time varies from a few seconds (no-load start) to a few dozen seconds (high-inertia load).

Trip Class of Overload Relays as a Function of Their FLA Setting

Class	1.05 FLA*	1.2 FLA*	1.5 FLA *	6.0 FL*
5	t > 2 h	t < 2h	t < 2 mn	2 s < t ≤ 5 s
10	t > 2 h	t < 2h	t < 4 mn	4 s < t ≤ 10 s
20	t > 2 h	t < 2h	t < 8 mn	6 s < t ≤ 20 s

Example: In class 20, the motor must have finished starting within 20 seconds
(6 to 20 s) for a starting current of 6 x FLA.

Asynchronous-Motor Starting Parameters

The main parameters of direct on-line starting of three-phase asynchronous motors (90% of all applications) are listed below.

FLA: full load amperes
This is the current drawn by the motor at full rated load.
Id: locked rotor current
This is the current drawn by the motor during starting, on average 6.0 x In for a duration of 5 to 30 seconds depending on the application. These values determine the trip class and any additional “long-start” protection devices that may be needed.
Id: peak starting current
This is the sub-transient current during the first two half-waves when the system is energized, on the average 14 In for 10 to 15 ms (e.g. 1840 A peak).

The protection settings must effectively protect the motor, notably through a suitable overload relay trip class, but let the peak starting current through.

Motor-Feeder Solutions

PowerPacT H-, J-, and L-frame circuit breakers motor circuit breakers are designed for motor-feeder solutions using:

three devices, including an electronic MCP or 1.3 M instantaneous-only trip unit
two devices including a 2 M electronic trip unit.

PowerPacT H-, J-, and L-Frame with MicroLogic Trip Units Motor-Protection Range

PowerPacT H-, J-, and L-frame circuit breakers with MicroLogic trip units can be used to create motor-feeder solutions comprising two or three devices. The protection devices are designed for continuous duty at 104°F (40°C).

Three-device solutions

1 PowerPacT circuit breaker with MicroLogic 1.3 M trip unit
1 contactor
overload relay

Two-device solutions

1 PowerPacT circuit breaker with a MicroLogic 2 M electronic trip unit.
1 contactor

Motor Protection Specifications

Type of Motor Protection			3 Devices (Circuit Breaker + Contactor + Overload Relay)	2 Devices (Circuit Breaker + Contactor)
PowerPacT H-, J-, or L-Frame Circuit Breaker			PowerPacT L-Frame 400/600 A	PowerPacT H-, J-, and L-Frame 100–600 A
	Type 2 Coordination with:		Contactor + Overload Relay	Contactor
Trip Unit	Type		MicroLogic 1.3 M Electronic Trip Unit	MicroLogic 2 M Electronic Trip Unit
Overload Relay	Separate		X
	Built-in, Class:	5		X
		10		X
		20		X
Protection Functions of PowerPacT H-, J-, and L-Frame Circuit Breaker
Short Circuits			X	X
Overloads				X
Special Motor Functions	Phase Unbalance			X

Electronic Motor Circuit Protectors (AC Only)

PowerPacT H- and J-frame Electronic Motor Circuit Protectors (MCP) are instantaneous-trip circuit breakers. They are designed to offer short-circuit protection and are National Electrical Code^® (NEC^®) compliant when installed as part of a combination controller having motor overload protection. MCP circuit breakers accept the same accessories and terminals as the equivalent thermal-magnetic circuit breakers. (See Accessories and Auxiliaries for Accessories.)

The unique design of the PowerPacT MCPs includes two rotary switches to allow quick setting adjustments based on the characteristics of the motor.

The first rotary switch allows for Full Load Amperes (FLA) adjustment across the range of the frame size.

The second rotary switch selects the type of motor protection based on Automatic 1 for Standard Efficiency or Automatic 2 for High Energy Efficient. When using the automatic settings the MCP microprocessor automatically adjusts the trip settings for both current and time to align with the start-up characteristic for the motor type, whether it is a standard or energy-efficient motor. This includes a dampening means to accommodate a transient motor in-rush current without nuisance tripping of the circuit breaker. Rotary switch 2 also allows for traditional motor protection from 8 to 13 times the selected FLA.

The MCP rotary switches allow the device to be set to specific trip values within a typical accuracy range of +/-5%.

Full Load Ampere Settings

Determine the motor’s full-load current by referring to the nameplate on the motor.
Set the trip range by turning the FLA rotary switch to the setting closest to the motor’s full load current.

Automatic Protection Settings

The MCP microprocessor automatically adjusts the trip settings for both current and time to align with the start-up characteristics for the motor type selected. This includes a dampening means to accommodate a transient motor in-rush current without nuisance tripping of the circuit breaker.

Automatic Protection Settings

Manual Protection Settings

The manual settings may be adjusted to multiples of current based on the rotary switch setting for motor Full Load Amperes (FLA).

Instantaneous
Trip Point

(FLA) x (I_m)

For example, if FLA rotary switch is set to 20 and I_m rotary switch is set to 9x, then the instantaneous trip point will be 180 A.

See Additional Technical Characteristics for more information.

H- and J-Frame Electronic Motor Circuit Protectors (MCP)

Frame	Current	Full Load Amperes Range	Adjustable Instantaneous Trip Range	Suffix	J Interrupting	L Interrupting*	R Interrupting*
Frame	Current	Full Load Amperes Range	Adjustable Instantaneous Trip Range	Suffix	Cat. No.	Cat. No.	Cat. No.
H-Frame	30 A	1.5–25 A	9–325 A	M71	HJL36030M71	HLL36030M71	HRL36030M71
	50 A	14–42 A	84–546 A	M72	HJL36050M72	HLL36050M72	HRL36050M72
	100 A	30–80 A	180–1040 A	M73	HJL36100M73	HLL36100M73	HRL36100M73
	150 A	58–130 A	348–1690 A	M74	HJL36150M74	HLL36150M74	HRL36150M74
J-Frame	250 A	114–217 A	684–2500 A	M75	JJL36250M75	JLL36250M75	JRL36250M75

High Short-Circuit Current Ratings (SCCR)
The PowerPacT MCP helps achieve the high UL508A Short-Circuit Current Rating (SCCR) needed to meet NEC Article 409 requirements for industrial control panels. They deliver up to 100 kA at 480 Vac SCCR when used in combination with approved Square D NEMA or Schneider Electric IEC motor starters.

Short-Circuit Current Ratings (SCCR)

Contactor/Starter	J Interrupting			L Interrupting			R Interrupting
Contactor/Starter	200–240 Vac	480 Vac	600 Vac	200–240 Vac	480 Vac	600 Vac	200–240 Vac	480 Vac	600 Vac
TeSys D-line and F-line	100 kA	65 kA	25 kA	100 kA	100 kA	50 kA	200 kA	200 kA	100 kA
NEMA Type S	100 kA	65 kA	25 kA	100 kA	100 kA	50 kA	200 kA	200 kA	100 kA

MCP Selection by HP Ratings of Induction-Type Squirrel-Cage and Wound-Rotor Motors

Horsepower Rating of Induction-Type Squirrel-Cage and Wound-Rotor Motors 3Ø 60 Hz					NEC Full Load Amperes	PowerPacT H-Frame and J-Frame Electronics MCP
Starter Size	200 Vac	230 Vac	480 Vac	575 Vac	NEC Full Load Amperes	PowerPacT H-Frame and J-Frame Electronics MCP
				1/2	0.9 A	HJL36030M71 and HLL36030M71 1/2 — 10 hp
			1/2		1.1 A
				3/4	1.3 A
			3/4	1	1.7 A
			1		2.1 A
		1/2			2.2 A
				1–1/2	2.4 A
	1/2				2.5 A
				2	2.7 A
			1–1/2		3 A
00		3/4			3.2 A
			2		3.4 A
	3/4				3.7 A
				3	3.9 A
		1			4.2 A
	1				4.8 A
			3		4.8 A
		1–1/2		5	6 A
					6.1 A
		2			6.8 A
	1–1/2				6.9 A
			5		7.6 A
	2				7.8 A
0				7–1/2	9 A
		3			9.6 A
	3		7–1/2	10	11 A
			10		14 A		HJL36050M72 and HLL36050M72 10–25 hp
		5			15.2 A
				15	17 A
1	5				17.5 A
			15		21 A
		7–1/2		20	22 A
	7–1/2				25.3 A
			20	25	27 A
2		10			28 A
				30	32 A	HJL36100M73 and HLL36100M73 15–50 hp
	10				32.2 A
			25		34 A
			30		40 A
				40	41 A
		15			42 A
	15				48.3 A
3			40	50	52 A
		20			54 A
	20			60	62 A		HJL36150M74 and HLL36150M74 30–100 hp
			50		65 A
		25			68 A
			60	75	77 A
	25				78.2 A
		30			80 A
	30				92 A
4			75		96 A
				100	99 A
		40			104 A	JJL36250M75 and JLL36250M75 50–150 hp
	40				120 A
			100		124 A
				125	125 A
		50			130 A
				150	144 A
	50				150 A
5		60			154 A
			125		156 A
	60				177.1 A
			150		180 A
		75		200	192 A
	75				221 A
			200		240 A
		100			248 A
Shaded area is not covered by J-Frame electronic motor circuit protector.

MicroLogic 1.3 M Electronic Trip Units for Instantaneous Protection Only (L-Frame Circuit Breakers Only)

MicroLogic 1.3 M trip units are used in 3-device motor-feeder solutions on PowerPacT L-frame circuit breakers with performance levels G/J/L. They provide short-circuit protection for motors up to 250 kW at 400 V.

MicroLogic 1.3 M trip units provide instantaneous protection only, using electronic technology. They are dedicated to 600 A three-pole (3P 3D) circuit breakers or four-pole circuit breakers with detection on three poles (4P, 3D). They are especially used in three-pole versions for motor protection.

Circuit breakers equipped with MicroLogic 1.3 M trip units, without thermal protection, are used in certain applications to replace automatic switches. MicroLogic 1.3 M trip units are available on PowerPacT L-frame circuit breakers only.

NOTE: All MicroLogic trip units have a transparent, sealable cover that protects access to the adjustment rotary switches.

They also provide the benefits of electronic technology:

accurate settings
tests
“Ready” LED.

Circuit breakers with a MicroLogic 1.3 M trip unit are combined with a overload relay and a contactor.

Protection settings are made using a rotary switch.

Protection Version

Three pole (3P): three-pole frame circuit breakers equipped with detection on all three poles.

Indications

The green “Ready” LED blinks slowly when the electronic trip unit is ready to provide protection. It indicates the trip unit is operating correctly.

NOTE: All the trip units have a transparent sealable cover that protects access to the adjustment rotary switches.

MicroLogic 1.3 M Electronic Trip Unit

Rating: In at 104°F (40°C)*		400 A	600 A
Circuit Breaker	PowerPacT L-frame	X	X
Short-time protection
Pick-up (A) accuracy ±15%	Isd There is a very short delay to let through motor starting currents.	Adjustable directly in amperes
Pick-up (A) accuracy ±15%		9 settings: 2000-2400-2800-3200-3600-4000-4800 A	9 settings: 3000-3600-4200-4800-5400-6000-6600-7200 A
Time delay (ms)	tsd	Non-adjustable
Time delay (ms)	Non-tripping time Maximum break time	20 60
Instantaneous protection
Pick-up (A) accuracy ±15%	Ii non-adjustable	4800	7200
Pick-up (A) accuracy ±15%	Non-tripping time Maximum break time	0 30 ms

MicroLogic 2.2 M and 2.3 M Electronic Trip Units

MicroLogic 2.2 M and 2.3 M trip units provide built-in thermal and instantaneous protection. They are used in two-device motor-feeder solutions on PowerPacT H-, J-, and L-frame circuit breakers with performance levels J/L. They provide protection for motors up to 315 kW at 400 V against:

short-circuits
overloads with selection of a trip class (5, 10 or 20)
phase unbalance.

Circuit breakers with a MicroLogic 2.2 M / 2.3 M trip unit include protection similar to an inverse-time overload relay. They are combined with a contactor.

Protection settings are made using a rotary switch.

Overloads (or Thermal Protection)

Long-time protection and trip class (FLA)

Inverse-time thermal protection against overloads with adjustable pick-up FLA.
Settings are made in amperes. The tripping curve for long-time protection, which indicates time delay tr before tripping, is defined by the selected trip class.

Trip Class

The class is selected as a function of the normal motor starting time.

Class 5: starting time less than 5 s
Class 10: starting time less than 10 s
Class 20: starting time less than 20 s

For a given class, all motor-feeder components must be sized to carry the 6 x FLA starting current without excessive temperature rise during the time corresponding to the class.

Short Circuits

Short-time protection (I_sd)

Provides protection with an adjustable pick-up I_sd.
There is a very short delay to let through motor starting currents.

Non-adjustable instantaneous protection (l_i)

Instantaneous protection with non-adjustable pick-up l_i.

Phase Unbalance or Phase Loss (l_unbal)

This function opens the circuit breaker if a phase unbalance occurs that is greater than the 30% fixed pick-up I_unbal following the non-adjustable time delay t_unbal equal to:

0.7 s
4 s during normal operation

Phase loss is an extreme case of phase unbalance and leads to tripping under the same conditions.

Indications

Front indications

The green “Ready” LED blinks slowly when the electronic trip unit is ready to provide protection. It indicates the trip unit is operating correctly.
Red alarm LED for motor operation goes ON when the thermal image of the rotor and stator is greater than 95% of the permissible temperature rise.

Remote indications using SDTAM module

PowerPacT H-, J-, and L-frame devices with a MicroLogic 2 M trip unit can be equipped with an SDTAM module dedicated to motor applications for:
— A contact to indicate circuit-breaker overload.
— A contact to open the contactor. In the event of a phase unbalance or overload, this output is activated 400 ms before circuit-breaker tripping to open the contactor and avoid circuit breaker tripping

This module takes the place of the shunt trip (MN)/undervoltage trip (MX) coils and an auxiliary switch (OF) contact

SDTAM remote indication relay module with its terminal block.

NOTE: All the trip units have a transparent sealable cover that protects access to the adjustment rotary switches.

MicroLogic 2.2 M and 2.3 M Electronic Trip Unit

Rating: In at 104°F (40°C)*			30 A	50 A	100 A	150 A	250 A	400 A	600 A
Circuit Breaker	PowerPacT H-frame		X	X	X	X	—	—	—
	PowerPacT J-frame		—	—	—	—	X	—	—
	PowerPacT L-frame		—	—	—	—	—	X	X
Overloads (or Thermal Protection): Long-Time Protection and Trip Class
Pick-Up (A) Tripping between 1.05 and 1.20 FLA	FLA		Value depending on trip unit rating (In) and setting on rotary switch
	In = 30 A	FLA =	14	16	18	20	21	22	23	24	25
	In = 50 A	FLA =	14	17	21	24	27	29	32	36	42
	In = 100 A	FLA =	30	35	41	45	51	56	63	71	80
	In = 150 A	FLA =	58	71	78	86	91	97	110	119	130
	In = 250 A	FLA =	114	137	145	155	163	172	181	210	217
	In = 400 A	FLA =	190	210	230	250	270	290	310	330	348
	In = 600 A	FLA =	312	338	364	390	416	442	468	484	520
Time Delay
Trip Class			5	10	20
Time Delay (s) Depending on selected trip class	tr	1.5 x FLA	120	240	480	For warm start
		6 x FLA	6.5	13.5	26	For cold start
		7.2 x FLA	5	10	20	For cold start
S Short Circuits: Short-time protection with fixed time delay
Pick-up (A) accuracy ±15%	Isd = FLA x		5	6	7	8	9	10	11	12	13
Time delay (ms)	tsd		Non-adjustable
	Non-tripping time		20
	Maximum break time		60
I Short Circuit: Non-adjustable instantaneous protection
Pick-up (A) accuracy ±15%	Ii non-adjustable		450	750	1500	2250	3750	4800	7200
Time delay (ms)	Non-tripping time		0
Time delay (ms)	Maximum break time		30 ms
Phase unbalance or phase loss
Pick-up (A) accuracy ±20%	I_unbalin % average current*		30%
Time delay (ms)	Non-adjustable		0.7 s during starting 4 s during normal operation

Additional Technical Characteristics

Unbalance of Phase Currents and Voltages

Motor Starting and Long Starts

Phase unbalance

An unbalance in three-phase systems occurs when the three voltages are not equal in amplitude and/or not displaced 120° with respect to each other. It is generally due to single-phase loads that are incorrectly distributed throughout the system and unbalance the voltages between the phases.
These unbalances create negative current components that cause braking torques and temperature rise in asynchronous machines, thus leading to premature aging.

Phase loss

Phase loss is a special case of phase unbalance.

During normal operation, it produces the effects mentioned above and tripping must occur after four seconds.
During starting, the absence of a phase may cause motor reversing, i.e. it is the load that determines the direction of rotation. This requires virtually immediate tripping (0.7 seconds).

Starting time in compliance with the class (MicroLogic 2 M)

For normal motor starting, MicroLogic 2 M checks the conditions below with respect to the thermal-protection (long-time) pick-up FLA:

current > 10% x FLA (motor-off limit)
overrun of 1.5 x FLA threshold, then return below this threshold before the end of a 10 s time delay.

If either of these conditions is not met, the thermal protection trips the device after a maximum time equal to that of the selected class. Pick-up FLA must have been set to the current indicated on the motor rating plate.

Starting time in compliance with the class (MicroLogic
2 M)

For normal motor starting, MicroLogic 2 M checks the conditions below with respect to the thermal-protection (long-time) pick-up FLA:

current > 10% x FLA (motor-off limit)
overrun of 1.5 x FLA threshold, then return below this threshold before the end of a 10 s time delay

If either of these conditions is not met, the thermal protection trips the device after a maximum time equal to that of the selected class.

Pick-up FLA must have been set to the current indicated on the motor rating plate.

L-Frame Electronic Trip Unit Magnetic Only Three-Pole, 600 Vac, 50/60 Hz—Three Device Solutions

Sensor Rating		Trip Unit	Adjustable Trip Range (A)*	G Interrupting Cat. No.	J Interrupting Cat. No.	L Interrupting Cat. No.	R Interrupting Cat. No.
PowerPacT L-Frame*	400	1.3 M	500–1200%	LGL36400M37X	LJL36400M37X	LLL36400M37X	LRL36400M37X
PowerPacT L-Frame*	600	1.3 M	500–1200%	LGL36600M37X	LJL36600M37X	LLL36600M37X	LRL36600M37X

H-Frame (150 A), J-Frame (250 A) and L-Frame (600 A) Electronic Motor Protector Circuit Breakers (UL Ratings)—Two Device Solutions

Electronic Trip Unit Type*	Frame	Sensor Rating	Trip Unit	FLA Range	Isd (x FLA)	G Interrupting Rating Cat. No.	J Interrupting Rating Cat. No.	L Interrupting Rating Cat. No.	R Interrupting Rating Cat. No.
Standard*	H	30	2.2 M	14–25	5-13 x FLA	HGL36030M38X	HJL36030M38X	HLL36030M38X	HRL36030M38X
		50		14–42	5-13 x FLA	HGL36050M38X	HJL36050M38X	HLL36050M38X	HRL36050M38X
		100		30–80	5-13 x FLA	HGL36100M38X	HJL36100M38X	HLL36100M38X	HRL36100M38X
		150		58–130	5-13 x FLA	HGL36150M38X	HJL36150M38X	HLL36150M38X	HRL36150M38X
	J	250		114–217	5-13 x FLA	JGL36250M38X	JJL36250M38X	JLL36250M38X	JRL36250M38X
	L	400	2.3 M	190–348	5-13 x FLA	LGL36400M38X	LJL36400M38X	LLL36400M38X	LRL36400M38X
	L	600	2.3 M	312–520	5-13 x FLA	LGL36600M38X	LJL36600M38X	LLL36600M38X	LRL36600M38X

Motor Circuit Protection

General Information

Motor Branch Circuit Protection Function

Switching

Basic Protection

Additional Electronic Protection

Trip Class of an Overload Relay Device

Trip Class of Overload Relays as a Function of Their FLA Setting

Asynchronous-Motor Starting Parameters

Motor-Feeder Solutions

PowerPacT H-, J-, and L-Frame with MicroLogic Trip Units Motor-Protection Range

Motor Protection Specifications

Electronic Motor Circuit Protectors (AC Only)

Full Load Ampere Settings

Automatic Protection Settings

Automatic Protection Settings

Manual Protection Settings

H- and J-Frame Electronic Motor Circuit Protectors (MCP)

Short-Circuit Current Ratings (SCCR)

MCP Selection by HP Ratings of Induction-Type Squirrel-Cage and Wound-Rotor Motors

MicroLogic 1.3 M Electronic Trip Units for Instantaneous Protection Only (L-Frame Circuit Breakers Only)

Protection Version

Indications

MicroLogic 1.3 M Electronic Trip Unit

MicroLogic 2.2 M and 2.3 M Electronic Trip Units

Overloads (or Thermal Protection)

Trip Class

Short Circuits

Phase Unbalance or Phase Loss (lunbal)

Indications

MicroLogic 2.2 M and 2.3 M Electronic Trip Unit

MicroLogic 2.2 M and 2.3 M Electronic Trip Unit

Additional Technical Characteristics

Unbalance of Phase Currents and Voltages

Motor Starting and Long Starts

L-Frame Electronic Trip Unit Magnetic Only Three-Pole, 600 Vac, 50/60 Hz—Three Device Solutions

H-Frame (150 A), J-Frame (250 A) and L-Frame (600 A) Electronic Motor Protector Circuit Breakers (UL Ratings)—Two Device Solutions

Phase Unbalance or Phase Loss (l_unbal)