Racking CB's

[Rags004]

Greetings. I have a question about the proceedure of "racking circuit breakers". I would assume that this is routine maintenance and is done to make sure electrical connections are in good physical order. However, I would like to know a little more about this procedure. The CB lit I have tells me the proceedure for doing it, but not much else.

 

[Zogzog]

What kind of breaker are you talking about? There are many different racking mech types and interlocks.

Keep in mind that racking of breakers is one of th most common tasks for an arc flash to occur and should only be done by qualified personel, trained in the construction and operation of the equipment wearing the proper PPE.

 

[dpc]

Breakers are racked in and out to connect and disconnect them from the bus. A "racked out" breaker is not connected to the bus.

It is an operational procedure that allows a full disconnect of the breaker from the energized bus. It is not really a maintenance procedure.

This only applies to draw-out type breakers.

 

[Rags004]

Thanks to both of you. This was in relation to several large static trip units. I am aware of the arc flash hazard here. As it turns out the question was put to me while I was doing an arc flash analysis, Why would you "rack in and out a live CB?" Having done AF analysis for three years now, I feel that if we can't engineer down the HRC, we need to get people to de-energize the circuit. This was a Cat 4 switchboard. Testing PPE here would be like testing a bullet proof vest. So I am left still wondering why it is necessary to disconnect the CB unless there is a pressing maintenance need on the CB itself.

Thanks

 

[Zogzog]

To do routine maintenence on the circuit breaker , or to lock out the breaker for working on the system downstream, it must be racked out of the switchgear, shutting down the entire system is not always an option. There are several ways to engineer out or reduce the hazard, we do it everyday. Arc Flash reduction switches are one way, another popular way to deal with this problem is remote racking systems.

http://www.remoterackingsolutions.com/

 

[stevenal]

A circuit is considered to be deenergized for work after it is visibly isolated, tested and grounded. Openning the breaker alone does not satisfy the first requirement. Openning the breaker and racking it out does. I suggest you implement remote racking. Moving upstream to deenergize the entire bus is unlikely to improve the the incident energy level encountered during the isolate, test, and ground procedure.

 

[Zogzog]

"static trip units" is not a breaker type, it is a trip unit and that type can be on any breaker so cant help you much on any specifics without the breaker type.