MITSUBISHI ELECTRIC Low-voltage Products
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Frequently Asked Questions

MCCB, ELCB, and Others
Specifications/Configuration

What is the setting of the overcurrent characteristic setting control of electronic breakers when the products are shipped?

Unless we receive specific instructions, the adjustment control for the overcurrent trip characteristic is set to maximum when the products are shipped. However, the pre-alarm is set to the minimum value (70%).

When we have to change the breaker's overcurrent and earth-leakage trip characteristic, will it cause any problems if we turn an adjustment control?

The settings of the adjustment controls and the switchover screw should only be altered by someone with specialist electrical knowledge.

When adjusting settings, switch the master breaker OFF or switch OFF or trip the breaker that will be reset, and ensure that the power is off.

Working with live wires carries the risk of accidents such as electric shocks or, in the event of a short circuit, arc burns.

In older models, in some cases the setting will revert to its minimum value when it is being changed, and modifying the settings while current is being carried can be dangerous due to the possibility of the unit tripping spontaneously. (Reversion to the minimum setting does not occur in current models).

What is the temperature range for storage of the no-fuse and ELCB, etc.?

The no-fuse and ELCB and others can be stored between -25 and +55°C.

However, even for short-term storage, ensure that the environment is free from condensation and ice.

MCCB, ELCB, and Others
Mounting and connection

We don't have much space on our boards. Can the no-fuse and ELCB and others be close-mounted?

If there is no difficulty in ensuring an insulating distance around live parts such as the terminal bars, the units can be used close-mounted and operated at load currents of 80% or less of rated current.

However, in the case of the ELCB, the effect of the magnetic field might cause unwanted operation if a current of 2,500 A or more flows through a neighboring breaker. In these circumstances, please ensure a distance of 50 mm or more between the units.

In addition, when an SHT or UVT is mounted, the effect of the magnetic field might cause unwanted operation when a current of 50 kA or more flows through a neighboring breaker. In these circumstances, please ensure a distance of 50 mm or more between the units.

Can we convert the unit for back connection rather than front connection?

We sell connecting parts for the back surface including terminals, terminal blocks, and mounting frames, and customers can therefore convert the units. (With the exception of units with 400A or higher electrically-operated devices).

Please see the Mounting and Connection section of our catalogue for information on the designations of the connecting parts that we sell and the applicable models.

Details of methods of conversion can be found in the instruction manual shipped with the unit, and in the "Type of Connection" section of Handling and Maintenance.

MCCB, ELCB, and Others
Features and external configuration

What temperature range can the breakers be used in?

The temperature range for all the breakers, including ELCB, earth leakage relays, and circuit protectors, etc. in addition to MCCB, is -10°C to 40°C. (However, the average figure for a 24-hour period should not exceed 35°C.)

The overcurrent trip characteristic of the breakers is adjusted for a standard surrounding temperature of 40°C when shipped.

(Circuit protectors and safety breakers are set for a basic surrounding temperature of 25°C.)

MCCB, ELCB, and Others
Technical terms/Other

What is the AL (alarm switch)?

The AL (alarm switch) is a switch that electrically displays the trip status of the breaker.

The operation of the switch and the signal to the terminal are shown below.

Switch operation
What is the AX (auxiliary switch)?

The AX (auxiliary switch) is a switch that electrically displays the ON/OFF status of the breaker.

The operation of the switch and the signal to the terminal are shown below.

Switch operation
What is the SHT (voltage trip device)?

The SHT is an inbuilt device enabling the breaker to be tripped remotely.

  • The allowable operating voltage range is 85%–110% of rated voltage in the case of AC, and 75%–125% of rated voltage in the case of DC.
  • Durability (number of trips) is 10% of the maximum number of times for opening and closing of the breaker.

* Please see the Auxiliary Equipment section of our catalogue for further details (coil rating, etc.).

What is the UVT (under voltage trip)?

The UVT is an inbuilt device that trips the breaker when the circuit voltage drops to 35%–70% or below, and that allows the unit to be switched ON following manual resetting when the voltage has recovered to at least 85%.

There are two types of UVT: A "resettable" type, which can be reset even when non-excited, and a "reset prevention" type, which cannot be reset when non-excited.

The following points should be noted when using a UVT.

  • (a)

    Always reset or conduct input with the UVT coil at rated voltage.

  • (b)

    Durability (number of trips) is 10% of the maximum number of times for opening and closing of the breaker.

  • (c)

    Do not reset the breaker (in the case of the reset prevention type) or conduct input (in the case of the resettable type) with the UVT non-excited, because this will result in early breakdown due to wear of the trip latch.

  • (d)

    A small breaker or a fuse must be set in the UVT circuit.

* Please see the Auxiliary Equipment section of our catalogue for further details (feasibility of manufacture, coil rating, etc.).

How does a selective breaker system work?

This is a method of circuit protection in which only the breaker directly related to a circuit in which a short circuit occurs goes into operation, while electricity supply continues to other unaffected circuits. In specific terms, only a particular branch breaker goes into operation, while the master breaker and other branch circuit breakers do not operate.

Generally, a selective breaker system can ensure a breaking capacity up to the instantaneous trip current for the master breaker, but if breakers with excellent current limiting performance are used for the branch breakers and the current to the master breaker can be minimized, the breaking capacity of the selective breaking system can be increased.

The breaking capacity of a selective breaking system will also be increased by the use of electronic breakers or air circuit breakers, which generally have higher instantaneous trip currents, for the master breaker.

How does a cascade breaker system work?

This is a system in which backup protection is provided by the main circuit breakers when the estimated short-circuit current at the position in which a branch breaker is located exceeds the breaking capacity of the branch breaker.

Cascade systems are also employed for economic efficiency when the breaking capacity of the breakers in a system becomes insufficient due to increases in the power of the electricity supply system.

The use of cascade breaker systems is regulated by Article 37 of the Electrical Installation Engineering Standards.

Manufacturers offer various combinations of breakers to make up cascade systems, offering supporting data from tests of combinations of two breakers.

Please refer to our own cascade breaking figures for the combinations that can be used in the Choices section of our catalogue.

What does the pre-alarm mean?

This is a function associated with electronic breakers.

The pre-alarm offers a warning if a load current in excess of the set value (rated current or below) is flowing continuously.

This warning enables measures to be taken to avoid power shutdown.

The set value for the pre-alarm can be adjusted.

What does "instantaneous tripping" mean?

This refers to tripping that occurs immediately when a short-circuit current or other comparatively high overcurrent is detected in the circuit.

MCCB and ELCB
Specifications/Configuration

How much power do the breakers consume?

The power consumption of the MCCB is shown in the Features and Performance section of the collection of materials on MCCB.

The power consumption of the ELCB is shown in the Features and Performance section of the collection of materials on ELCB.

The amount of heat generated by the units can be calculated by multiplying the amount of power consumed by time. ... 1J=1W (power consumed) × S (second)

MCCB and Others
Mounting and connection

Can we use a two-pole breaker as a one-pole breaker?

A two-pole breaker should not be used as a one-pole breaker (one-pole connection for single phase and single pole). Please note the information in (1) and (2) below.

  • (1)

    If a two-pole MCCB is used as a one-pole breaker, the unit may not trip at 125% of rated current, or the procedure may take more time. (Operation cannot be guaranteed at 125%). From the perspective of regulations also, no regulations cover the trip performance of a single pole of a two- or three-pole breaker at 125%, and we do not conduct operating tests prior to shipping by applying 125% of rated current to single poles.
    However, no problems will be encountered in using a single pole for tripping at 200% or more of rated current or for opening and closing the current at rated current or below. (Applicable circuit voltages are shown in (2) below.)

  • (2)

    When two-pole MCCB are used as one-pole breakers, single-pole breaking performance, assuming a ground fault, is as follows:

Two-pole MCCB with a breaking capacity exceeding AC5000A have single-pole breaking performance of AC5000A.

Single-pole breaking performance (applicable voltage) for breakers with a rated voltage exceeding AC265V is up to AC265V.

ELCB and Others
Specifications/Configuration

How do the test buttons and trip buttons on the ELCB function?
Test button

Pushing the test button enables the user to test whether the breaker will operate correctly (trip) when an earth leak occurs. An earth leakage display button protrudes to enable earth leakage operation during this test.

However, voltage must be present in the main circuits to enable testing of electrical operation.

Trip button

Pushing the trip button mechanically trips the breaker, based on the assumption of an overcurrent trip. This button is used when checking the operation of the mechanical section, the alarm switch (AL), etc.

The earth leakage display button does not protrude when the trip button is used.

ACB (AE)
Selection

Can these units be used for ground-fault protection and earth-leak protection?

Not at the same time.
One function must be selected.

ACB (AE)
Specifications/Configuration

What is the difference between breakers for generator protection and breakers for general protection?

AE air circuit breakers also basically possess specific trip characteristics and functions in order to protect wiring.

AE air circuit breakers are widely used in generator circuits, and we therefore also offer relays for generator protection, with special trip characteristics for generator protection.

In the case of relays for generator protection, the rated current is a designated value corresponding to the rated current of the generator, and adjustment of the 120% time limit and fine adjustment of the long delay current setting in line with the excess load characteristic of the generator is also possible.

MDU breaker
Technical terms/Other

What is an MDU breaker?

An MDU breaker is a breaker which is integrated with a measuring display unit (MDU) that measures, displays and transmits information on electrical pathways.

A CT and VT are built into the breaker to enable measurement of current and voltage.