Size of 2 breakers on same circuit

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NEC User

Senior Member
My design has a 45A breaker in a distribution panel to feed a load using #2 AWG cables (for voltage drop). My client has standard drawings that shows installation of a 100A breaker just prior to the load (a traffic sign). The load for the traffic sign is only 25A max. The 45A breaker and 100A breaker are spaced roughly 500 feet apart.

Is it a code violation to have a 45A breaker feed a 100A breaker located so far away? My thoughts are no since the cables are protected by the 45A breaker and the 45A breaker will trip and thus protect the wires. Thus, the 100A breaker simply acts as a disconnect. Is there any code requiring the breaker closest to the load to trip first?
 

templdl

Senior Member
Location
Wisconsin
Breakers protect cable. The cable is sized to carry the load. Is the wire protected? Unless the device manufacture specifies that a specific OCPD be used to protect it.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Is there any code requiring the breaker closest to the load to trip first?
The rules for "selective coordination" only apply to specific installations, such as emergency or legally required standby systems. The purpose is to ensure that a fault does not cause a loss of power to anything upstream of that "closest breaker." Note that in your case, whichever breaker trips first (or even if they both trip), the total number of loads that lose power are exactly the same. So even if you could select breaker ratings and trip settings so as to achieve selective coordination, it would not matter in terms of the impact of a fault on the operation of the system.

 

JDB3

Senior Member
What brand/type of breaker is going to be used? At a job I am working on, they had a 2 pole 60 amp for #2 hard drawn wire, it was pigtailed with #6 copper. I put one of the #2's on the breaker, & it did go. The other one did not? Upon closer inspection, I saw some strands had been cut. #2 would not go into the 60 amp breaker. I purchased a 90.
 
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