Line Induction
Line Induction
(OP)
Hello,
I'm planning to run a 500 Amp 60Hz AC line, secured to the ground by short 2" steel clamps spaced at certain intervals. If the clamps I used went around the whole cable and were closed metallically via a bolt, would there be any significant induced currents flowing in the clamp, such that the clamp itself would heat up?
Thanks!
EMan
I'm planning to run a 500 Amp 60Hz AC line, secured to the ground by short 2" steel clamps spaced at certain intervals. If the clamps I used went around the whole cable and were closed metallically via a bolt, would there be any significant induced currents flowing in the clamp, such that the clamp itself would heat up?
Thanks!
EMan






RE: Line Induction
If you use a separate clamp for each circuit conductor (or any other similar installation such that all conductors don't pass through the clamp), the net current through the clamp will not be zero. That will heat the clamp.
RE: Line Induction
Regards,
EMan
RE: Line Induction
RE: Line Induction
"(B) Individual Conductors. Where a single conductor carrying alternating current passes through metal with magnetic properties, the inductive effect shall be minimized by (1) cutting slots in the metal between the individual holes through which the individual conductors pass or (2) passing all the conductors in the circuit through an insulating wall sufficiently large for all of the conductors of the circuit. "
This is written more to address something like a steel escutcheon plate, but you'll get a similar effect with your clamps. BTW -- there's many half-circle shaped clamps available for electrical work with a tab for the fastener, you might consider something like that in lieu of your full-circle clamp. Alternately, perhaps you could use nylon wire ties to attach your cabling to a fastener.
I'm still concerned about you running wiring on the floor -- what's up with that? How are you protecting wiring fastened to the floor?
RE: Line Induction
The clamps in question are Unistrut's Cush-A-Clamps (as in the above pic), and ideally, we would like metal for strength in our application.
As a background, the current design calls for putting two of these side-by-side (but not touching). A circuit phase will go through each of these, and the third conductor would go in the central space on top between the clamps; all three cables will then be tie wrapped together.
Regarding the connection to the ground, I meant to simplify the issue by saying that the clamps would be mounted on the floor, but in actuality, their layout will span across an elevated, grounded tray.
I am wondering how big of a difference a semi-circular clamp would make, as I take it from the NEC quote that the generated currents are due to magnetization.
RE: Line Induction
RE: Line Induction
RE: Line Induction
RE: Line Induction
P-clamps might be more suitable for your application than U-bolts.
Also, have you considered installing all three conductors within a single clamp?
Why do you feel that cable ties are OK for 1/3 of your conductors? Why wouldn't you provide metal clamps for all or none of the cables?
See http://www.cooperbline.com/pdf/catalogs/CT02MAN.pdf for more info on ties & clamps.
RE: Line Induction