magnetic duct

[whycliffrussell]

For the purposes of short circuit calculations does anyone know if teck cable is considered 'magnetic duct' (due to the fact that it is encased in metallic armor)?

 

[davidbeach]

Steel armor - yes; aluminum armor - no.

 

[cuky2000]

The type of raceway may not have significant impact in the SC rating of the cable. This mainly is a function of the insulation withstand temperature (initial & Max.), the conductor material and the duration of the SC (protective device tripping characteristics).

The enclose link will help to illustrate the SC effect on cable.

http://cuky2000.250free.com/Cable_SC_IEEE-Std-242.jpg

 

[whycliffrussell]

I'm not concerned about the SC rating of the cable in this case - I'm am modeling an existing system and am only concerned with how the magnetic duct effects the cable impedance and hence the downstream short circuit.

 

[cuky2000]

For practical purposes, resistance is unaffected by the conduit or armor material (magnetic or nonmagnetic). However, cable reactance may vary significantly if compared with single conductor cables installed in conduit. A rough approximation may be estimated as follow:
a) For nonmagnetic armor consider approx 20% less reactance than 3 single conductor in magnetic conduit.
b) For magnetic armor, consider approx 50% less reactance than 3 single conductor in magnetic conduit.