rating of cable with 100% rated breakers

Status
Not open for further replies.
mshields

mshields

Senior Member
Location
Boston, MA
If you are protecting cable with a 100% rated breaker, should the cable be larger than it would be with an 80% rated breaker. e.g. if I've got a 1000A feeder, does my cable need to be rated for 1000A x 1.25%.

I believe cable is fully rated for whatever is listed in Table 310-15(B)16 but I'm having a moment of doubt.

thanks,

Mike
 
T

templdl

Senior Member
Location
Wisconsin
This is how I understand it:
Refer to NEC 210.19, 210.20, 215.2, 215.3 and 230.42 which permit conductors and overcurrent protection to be rated for 100 percent rather than 125 percent of continuous current ?where the assembly, including the overcurrent devices protecting the "circuit" is listed for operation at 100 percent of its rating.? It is important to note that the cable is to be 90degC rated but must be applied at 75degC.
As such one may be able to save by using a smaller cable size size depending upon where the cable ampacity ratings end up to be (100% of non-continuous loads + 100% of continuous loads instead of using 100% of non-continuous loads + 125% of continuous loads) as well as the distinct posibility of being able to use a smaller frame breaker. I believe the biggest savings may be provided by your ability to apply a smaller cable since the breaker manufacturer digs in your pocket a bit more for the 100% rated breaker for which the enclosure must be sized and rated for such an application.
 
Status
Not open for further replies.
Top