Motor Protection Circuit Breakers Selection Guide
A motor protection circuit breaker opens all poles together on overload with a bimetal and clears a short circuit with magnetic tripping; when choosing, look at the setting range, Ii, Icu and Ics.
This guide covers what to look at when choosing products in the Motor Protection Circuit Breakers category.
How a motor protection circuit breaker works
In the classic bimetal design, the motor current passing through each pole heats a bimetal. When the current exceeds the setting value, the breaker opens all poles together in a time that gets shorter as the excess grows. When one of the phases is lost, the bimetals do not heat equally and tripping is brought forward; phase loss sensitivity comes from this. Magnetic tripping acts without delay and is not adjustable in this design; its threshold is kept above a normal inrush current and appears on the product card as the rated instantaneous short-circuit current setting (Ii) (for example 150 A on the ABB MS132 set to 6.3-10 A).
IEC 60947-4-1 defines these devices as manually operated starters with short-circuit protection built into the housing. For this reason, product cards give the circuit breaker standard IEC 60947-2 alongside the starter standard, and the Icu and Ics values according to that standard.
What to look at when choosing
- Thermal setting range. The ranges are arranged in narrow steps such as 0.16-0.24 A, 4-6 A, 17-23 A, 45-63 A, and each step is a separate product. The current calculated from power is for preliminary selection only (the Current and Fuse Calculation from Active Power tool can be used for this); the setting is made according to the value on the motor label.
- Tripping type. Thermal-magnetic models include both protections; magnetic-only models are short-circuit elements only. The distinction is not written in every product name and is read from the code: at Schneider Electric, GV2ME, GV2P, GV3P and GV4P are thermal-magnetic and GV2LE, GV3L and GV4L are magnetic; in EasyPact TVS, GZ1E is thermal-magnetic and GZ1LE magnetic; at ABB, MS116, MS132 and MS165 are thermal-magnetic and MO132 is magnetic only.
- Short-circuit breaking capacity (Icu). It is compared with the prospective short-circuit current at the point where the breaker will be installed. Values such as 10 kA, 50 kA and 100 kA are listed in the category; the value varies with the current step and the voltage, and a value given for 400 V can be much lower at 690 V.
- Trip class. It is written as class 10 and class 10A on ABB product cards. For loads with long starting times, check from the manufacturer's tripping curve whether the class is sufficient.
- Housing and series. As the current grows, the housing grows too; at Schneider Electric, the TeSys series from GV2 to GV6 follow this order. Panel layout and the parts for joining with a contactor depend on the housing.
- Connection and accessories. Screw-connection and spring-connection models are listed with separate codes. Blocks that carry position and fault information to the control circuit are in Auxiliary Contacts; undervoltage and shunt trip coils, connection busbars and rotary handles are in the Switch Accessories category; an accessory must match the series of the breaker.
Use together with a contactor and thermal overload relay
A motor protection circuit breaker protects and opens and closes by hand; for remote or automatic control, a contactor is added to the circuit. A thermal-magnetic breaker and a contactor form a two-element starter. When a magnetic-only breaker is used, overload protection is provided by a thermal overload relay connected to the contactor; in this arrangement an overload trip drops out the contactor, the breaker stays set, and the two faults can be monitored separately. The compatibility of the breaker, contactor and relay with one another is selected from the manufacturer's coordination tables. Enclosed starters and soft starters are in the Motor Starters category.
Star-delta and drive circuits
In star-delta starting, the thermal setting depends on where the protective element sits in the circuit: the breaker at the line input sees the line current and is set to the motor's rated current; the overload element connected in the winding leg sees the phase current and is set to 1/√3 of the rated current (about 0.58 times). Starters used at the output of a frequency converter are outside the scope of IEC 60947-4-1; in a drive circuit, the position and type of the breaker are selected according to the data of the drive and breaker manufacturers.
Brands in this category
- Schneider Electric: TeSys GV2, GV3, GV4, GV5 and GV6 series and EasyPact TVS; thermal-magnetic and magnetic-only models.
- Siemens: 3RV2 and 3MV8 series; the product name states the thermal setting range.
- ABB: MS116, MS132 and MS165 thermal-magnetic, MO132 magnetic breakers. HK1 and SK1 are auxiliary and signal contact, UA1 undervoltage coil, and AA1 shunt trip coil codes.
- Chint: NS2 series 3-pole thermal-magnetic breakers.
Order notes
Products are sold by the piece. For models listed as made to order, the lead time is confirmed before the order. Because the setting steps of the same series differ only in the last digits of the code, search with the full manufacturer code such as GV2ME21 or 3RV2011-1JA10 and compare the setting range in the product name with the motor label.
Motor Protection Circuit Breaker (MPCB) Current Ranges and Selection Table
| Motor Power (400V 3-Phase) | Typical Full-Load Current | Thermal Setting Range (Ir) | Short-Circuit & Accessory Compatibility | Category / Spec Link |
|---|---|---|---|---|
| 0.37 kW – 0.75 kW Induction Motor | ~1.0 A – 2.0 A | 1–1.6 A or 1.6–2.5 A | Auxiliary contact (NO+NC) + undervoltage release compatible | 1.6-2.5 A Motor Protection Breakers |
| 1.5 kW – 2.2 kW Induction Motor | ~3.5 A – 5.0 A | 2.5–4 A or 4–6.3 A | Direct contactor link module and IP55 surface enclosure | 4-6.3 A Motor Protection Breakers |
| 3 kW – 4 kW Induction Motor | ~6.5 A – 8.5 A | 6–10 A | Phase-loss sensitive thermal-magnetic trip · 50–100 kA Icu | 6-10 A Motor Protection Breakers |
| 5.5 kW – 15 kW Induction Motor | ~11 A – 30 A | 9–14 A / 13–18 A / 20–25 A / 24–32 A | Door-mounted rotary handle and fault signaling contact | Motor Protection Circuit Breakers |
Frequently asked questions
What current should a motor protection circuit breaker be set to?
The thermal setting is brought to the rated current on the motor label that corresponds to the connection type and voltage in use; the breaker's scale is therefore in amperes. The current calculated from power is for preliminary selection only. In a star-delta starter, the breaker at the line input is set to the rated current, and the overload element connected in the winding leg to 1/√3 of it (about 0.58 times). For corrections such as ambient temperature, see the breaker manufacturer's data.
What is the difference between a motor protection circuit breaker and a thermal overload relay?
A thermal overload relay senses only overload and opens the contactor's coil circuit with its own auxiliary contact; it has no short-circuit tripping, so a fuse or breaker must sit upstream of it. A motor protection circuit breaker carries overload and short-circuit tripping in the same housing and opens the main circuit directly. Both are set to the motor current; the choice depends on whether the starter will be built with two elements or three.
Can a motor protection circuit breaker be used without a contactor?
In a motor that is started and stopped by hand, the breaker alone serves as the starter; IEC 60947-4-1 defines this device as a manually operated starter with short-circuit protection built into the housing. Where remote, automatic or frequent switching is needed, a contactor is added. If you do not want the motor to start by itself when power is cut and comes back, an undervoltage coil is fitted to the breaker or the control is built through the contactor.
Can a 3-pole motor protection circuit breaker be used on a single-phase motor?
It can in models the manufacturer allows, but the current must pass through all three poles. When only one or two poles are loaded, the bimetals do not heat equally and the breaker may trip early as if there were a phase loss; for this reason the poles are connected in series. Verify the wiring diagram and the voltage and breaking capacity values valid for single-phase from the product's user manual.
Can the setting be raised if a motor protection circuit breaker trips often?
Raising the setting above the label current leaves the overload protection ineffective; the cause of the tripping must be found first. If tripping occurs at start, the starting time and load are checked; if it occurs during operation, the current the motor draws, the phase voltages and the terminal block connections are checked. High ambient temperature can also bring thermal tripping forward. If tripping continues while the current is below the label value, the breaker and the motor should be checked by a qualified electrician.