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Methods Of Mounting LV Circuit Breakers
Methods Of Mounting LV Circuit Breakers

Three general groups

Methods used to mount circuit breakers can be divided into three general groups, those being:

  1. Fixed
  2. Removable (disconnectable unit), and
  3. Drawout (withdrawable)

A review of these mounting methods follows.


Fixed Mounted Circuit Breakers

Siemens fixed air circuit breaker
Siemens fixed air circuit breaker

A circuit breaker that is bolted in its enclosure and wired to the load frame, we can call a fixed mounted circuit breaker. These units are typically rated 600 volts or less and are front mountable. Power is provided to the breaker typically by wires or sectional type bus bars.

Power feeding the circuit breaker must be turned off in order to physically remove the fixed mounted breaker.

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Removable Mounted Circuit Breakers (Disconnectable units)

Removable disconnectable circuit breaker
Removable disconnectable circuit breaker (photo credit: electrical-installation.org)

A removable circuit breaker (Disconnectable unit) has two parts, a base, which is bolted to and wired to the frame, and the actual breaker, which has insulated parts that electrically mate with the base. This means of mounting allows the unit to be replaced with out re-wiring the unit on the line side of the breaker.

This type of mounting is typically used for breakers rated 600 volts or less.

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Drawout (Withdrawable) Mounted Circuit Breakers

Withdrawable Circuit Breaker
Withdrawable Circuit Breakers (on photo: ABB’s Emax Low voltage air circuit-breaker)

A drawout circuit breaker also has two parts, the base, which is bolted and wired to the frame and the actual breaker, which slides into and electrically mates with the base. This allows the unit to be replaced without having to turn off the power feeding the breaker.

The load must be turned off in order to test, remove or replace the unit.

As a safety feature these units are interlocked to automatically turn the power off just before removal of the breaker begins. By design, only the circuit breaker’s load must be turned off to remove the breaker. This method of mounting allows for a single breaker to be disconnected from the power supply.

That is to say that it does not require that all of the power be disconnected from all of the breakers installed in the larger enclosure such as a motor control center.

There are various designs used to facilitate the “racking-in”(installation) and “racking out”(withdrawal) of the drawout type circuit breaker. Commonly some form of jacking screw is used to initially move and thus electrically disengage the breaker, then a traveling trolley type of hoist (somewhat like a small boat winch) supports the breaker during removal and re-installation.

A transient supporting device is necessary as these sizes of breakers are too heavy and too bulky to be safely moved into and out of position by one person.

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Reference: Electrical Circuit Breakers – L.W. BRITTIAN Mechanical & Electrical Instructor

About Author //

author-pic

Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on

One Comment


  1. trongtrinhvan
    Aug 26, 2014

    hi Mr. Edvard i am everyday see the EEP new paper , i want see the single line for recloser, and same problem typical error-prone of it
    Thank yous

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