Induced Currents in Ferrous Metal Enclosures or Ferrous Metal Raceways

Status
Not open for further replies.

Adnan Hasan

Member
Location
baghdad, Iraq
section 300.20 Induced Currents in Ferrous Metal Enclosures or Ferrous Metal Raceways
(A) Conductors Grouped Together. Where conductors carrying alternating current are installed in ferrous metal enclosures or ferrous metal raceways, they shall be arranged so as to avoid heating the surrounding ferrous metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.
question:
1- does this section apply on all sizes of of conductors carrying alternating current?
2- how do I group conductors of different sizes in the same raceway (steel cable tray)? conductor sizes start from 14 to 1 AWG 3 cores per cable for single phase (230v 50Hz) and 4 cores per cable for 3 phases (400v 50Hz)
 

templdl

Senior Member
Location
Wisconsin
This is the way that I look at it otherwise you can generate some serious heating:
1)A single conductor that has alternating current through it will induce current to flow in the ferrous raceway that it runs through. Because the ferrous metal is not a very good conductor it will get warm and depending upon the magnitude of current running in that single conductor can get very hot. This also is true should you enter ferrous enclosure with a single conductor through a single hole even though when the wire is protected grommet that wire will induce current to flow in a circular fashion at the point where the wire enters the enclosure.
As such all wires that are used for that circuit must be run together such that their alternating magnetic fields cancel one another.
The only way that I'm aware of that you can enter an enclosure with a single wire is with a properly sized and installed nometalic glastic type material gland plate.
2) When running your conductor make sure that the circuits are run together as a set, that is you can run a single circuit together as a set or wore than one circuit as long as all of the conductors for each individual circuits are included for each circuit.
That way you will as sore that the magnetic fields for each wire balance out to zero.

I believe this is the basis of you question.
 
Status
Not open for further replies.
Top