What do the letters and numbers on the molded case circuit breaker mean? Teach you how to read nameplates

You must have seen plastic case circuit breakers (MCCB) in distribution boxes, factory floors or construction sites. The small nameplate on it is full of letters and numbers - Arm3, In, Icu, Ics... To those who are unfamiliar with it, these symbols are like a "heavenly book".

 

But as long as you understand their meaning, you can quickly determine whether a Circuit Breaker is suitable for your circuit. Today I will take Ruirui Electric’s products as an example and show you how to dismantle them one by one.

 

Model series code: such as ARM3, ARXM3, ARM5...

The first few letters of the molded case circuit breaker model are usually the manufacturer's own series code. Take Ruirui Electric as an example:

- ARM3 series: The main series of thermal magnetic molded case circuit breakers, with five frame levels of 125A, 250A, 400A, 630A, and 800A, with current coverage from 16A to 800A

- ARXM3 series: the same platform as ARM3, the same five frame levels

- ARM3E series: electronic molded case circuit breaker, equipped with electronic tripper, more complete protection functions

- ARM5 series: double breakpoint products with higher breaking capacity, up to 150kA-200kA

- ARM6 series: New energy-specific series, including DC photovoltaic model (ARM6DC) and AC high-voltage model (ARM6HU), etc.

The suffix number (such as 125, 250, 400, 630, 800) represents the frame level current, which is the maximum frame current specification that this circuit breaker can withstand.

> Tips: Circuit breakers with the same frame current have basically the same appearance and installation dimensions, but can be set to different rated currents.

 

Rated current In - one of the most important numbers

Common markings on the nameplate:

- In = 100A

- Rated current: 63A

This is the current that the circuit breaker can pass for a long time without tripping at a specified ambient temperature (usually 40°C). If it is too large, it will not provide protection; if it is too small, it will trip frequently.

> Practical experience: It is recommended that the long-term load current should not exceed 80%~90% of In. It is safer to leave a little margin.

 

Rated voltage Ue and insulation voltage Ui

- Ue (rated operating voltage): such as AC400V, AC690V, AC800V, AC1000V. The circuit breaker can normally break and close the circuit under this voltage

- Ui (rated insulation voltage): usually higher than Ue, most Ruirui products are 1000V. It determines the electrical clearance and creepage distance of the circuit breaker

Two voltages often appear on the nameplate at the same time. Remember: Ui ≥ Ue, and the system voltage cannot exceed Ue.

 

Breaking ability Icu and Ics - life-saving indicators

This is the number that is most easily overlooked by novices, but is actually the most critical.

- Icu (rated ultimate short-circuit breaking capacity): For example, Icu = 50kA. This means that the circuit breaker can successfully cut off a 50kA short-circuit current once, and may be scrapped afterwards, but it will not explode or catch fire.

- Ics (rated operating short-circuit breaking capacity): For example, Ics = 35kA. It means it can cut off 35kA short-circuit current and can continue to be used normally after cutting off.

 

Ruirui products are divided into four levels according to breaking capacity:

- Type C (economical type): Icu 35kA / Ics 22kA

- L type (standard type): Icu 50kA / Ics 35-50kA

- M type (higher breaking type): Icu 65-75kA / Ics 42-75kA

- Type H (high breaking type): Icu 100kA / Ics 65-75kA

> Selection principle: Icu is used for “life-saving bottom line”, and Ics is used for “daily reliability”. The expected short-circuit current of the distribution system should be ≤ Ics, at least ≤ Icu.

 

Pole number code: 3P / 4P

- 3P: three-pole, controlling three phases L1, L2 and L3 at the same time, neutral line straight through

- 4P: Four-pole, three-phase + N line is also controlled by the switch. Commonly used in main incoming lines or situations with leakage protection

 

Release type: thermal magnetic type vs electronic type

There is often a line of small words on the nameplate:

- Thermal magnetic type (TM): main configuration of ARM3/ARXM3 series

- Thermal bimetal is responsible for overload protection (inverse time limit)

- The electromagnetic coil is responsible for instantaneous protection against short circuits

- Electronic type (ETU): ARM3E series

- Multi-stage protection such as long delay, short delay, instantaneous and ground fault can be set

- Ruirui electronic products are equipped with 6 adjustable knobs, corresponding to the overload long delay current Ir1, long delay time tr1, short delay current Ir2, short delay time tr2, instantaneous current Ir3, and pre-alarm current Iro

- The panel is also equipped with indicator lights: green light (normal operation), yellow light (pre-alarm), red light (overload)

 

Breaking capacity code: C / L / M / H

Ruirui products usually have a letter at the end of the model number, which represents the breaking capacity level: 

| Code | Meaning | Typical Icu |

|------|------|---------|

| C | Economical type | 35kA |

| L | Standard type | 50kA |

| M | Higher breaking type | 65-75kA |

| H | High breaking type | 100kA |

For example: ARM3-630L means 630 frame, standard breaking capacity

 

Full interpretation of common nameplate examples

Let’s practice with an actual nameplate:

> ARXM3-125L/3300

> Ue AC400V / Ui 1000V

> In 100A

>Icu 50kA/Ics 35kA

> 3P

>50/60Hz

> IEC 60947-2

Translate it:

- ARXM3-125L: Ruirui 125 frame, L type (standard breaking type)

- 3300: Common internal code (3 poles + thermal magnetic + no accessories)

- Rated current 100A

- Limit breaking 50kA, running breaking 35kA

- Three-phase, suitable for 50/60Hz power supply

- Complies with IEC 60947-2 low voltage circuit breaker standard

Quick check of special function models

Ruirui also has some special-purpose models with additional markings on the nameplate:

- ARM3R: economical series, optimizing cost based on ARM3

- ARM6Z: Intelligent measurement switch with "four remote" functions (telemetry, remote signaling, remote control, remote adjustment), optional LCD screen display

- ARM5HU: high voltage series, suitable for AC1000V-1200V system

- With "overload alarm without tripping" function: meets the requirements of Article 6.3.6 of GB50054 to ensure the continuity of power supply

 

 A practical tip to help you remember

> Please refer to the series for the model number and In for the current.

> Look at Ue for voltage, and look at Icu for breaking

> The level depends on C/L/M/H, the number of poles is 3P or 4P

> For tripping, see TM/electronic type, for special purposes, see the suffix

 

write at the end

The nameplate of the molded case circuit breaker is not for good looks, but its "identity card" and "capability specification".

Next time you see the letters and numbers on the Ruirui electrical circuit breaker, you won't feel unfamiliar - In is the capacity, Icu is the confidence, Ics is the reliability, C/L/M/H is the breaking level, the number of poles determines the circuit, and the release determines the protection method.