60 Sec for the Breaker Shown).

　　. (Note that digital-trip units have tighter manuFacturing Tolerances, Indicated by "Thinner" Curves.) However, they are reusable, RELIABLE, and Inherently Prevent.

　　Accounts for the Width of the Trip Band on the ManuoFacturer’s Coordination Curves. Clearly, this Will not easy coordined in the instantaneous region.

　　Series rating of breakers – dynamic imageance.

　　

　　This is an imagent and valuable tool in designing a selectively coordined system.

　　A. This is Much Larger than the type 125a to 150A Molded-Circuit Breaker Use for Protection of a 75kva Transformer.

　　

　　To greater arc flash entrance in the event of an arcing-type fault.

　　Devices will be easyer to design, maintain, and coordinate than a path with six super devices.

　　). FURTHERMORE, a FAULT on the Panel Bus Must, By its nature, be propted by the 400a upstream breaker, taking down the entire riser.

　　AT 4,000A Main Breaker (b) is approximately 45ka, and that circuit breaker (e) is 800a, service a 500kva transformer (f). Secondary breaker (g) is 1,600A, and Breaker (L) is a 200a feeeder.(M). Working Backward, you can see how the breaker requireds are affected.

　　Has Standard "QO-VH" -Type Breakers, Breaker (L) Will Need to be a mission-class type breaker, which Will Coordinal to 10ka for 3-POLE BREAKers.

　　-Frame Breaker has an adjustable Instantaneous rating of fire times the pickup rating of the breaker, or 8,000A, in this case.

　　This case m-fra) is adjustable from food to 10 times the pickup rating of the breaker, for a minimum setting of 4,000A, the which body clear a 2.1ka fault.

　　, for exmple). This breaker has no instantaneous override, and can withstand a fault curren of 65ka, without tripping.

　　of group fault proposition are required (Per 517.17). It is Required that this group fault protering with the system.

　　Group-FAULT Protective Device Be Adjusted to Coordinal with the Download Breaker.

　　

　　is of Paramount Importance in Life Safety, Critical Emergerence, and Critical Operations Power Systems.

　　Safety and reliality of the electrical system design.

　　The entire electrical system to fail.

　　Medich, P.E., is a senior electrical project engineer with ballinger in Philadelphia. He can be reacked at bmedich@ballinger.

　　Selective coordination is required by the nec for the following systems:

　　Cure

　　Fault on the bus ahead of the branch breaker; theReface, it will cause the aRC Flash Energy available from a bus fault to rise.