Vitalink MC Cable

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infinity

infinity

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We've been running miles of Vitalink MC Cable for fire alarm and fire pump power. I've been told that according to the instructions you can space the cables like shown in the photo. I'm wondering, how this does not cause heating the surrounding ferrous metal by induction? Where is enters the steel enclosures a slot is cut between the individual KO's that complies with 300.20(B). Is it that a ferrous strut and strap about every 5' surrounding the cable is too small to cause any inductive heating?

20180727_120203 (1).jpg
 
It looks neat that way but back in eighties my boss made me carry a toy matchbox car with me... actually made a keychain of one... He had worked for a major manufacturer in both USA and Europe he found that One needed space between the conduits or you could have equipment problems. He insisted that the car was the perfect width to use for spacing wires above each other or for conduit spacing... he was boss so I did it.. never saw it in code, however, but still a GTO judge in my toolbox for that reason..plus car looks cool...lol
 
infinity said:
We've been running miles of Vitalink MC Cable for fire alarm and fire pump power. I've been told that according to the instructions you can space the cables like shown in the photo. I'm wondering, how this does not cause heating the surrounding ferrous metal by induction? Where is enters the steel enclosures a slot is cut between the individual KO's that complies with 300.20(B). Is it that a ferrous strut and strap about every 5' surrounding the cable is too small to cause any inductive heating?

View attachment 20898
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If that is not a problem then there shouldn't be a need to cut slots between KO's in the panel cabinet either. JMO. (assuming strut and clamps are indeed ferrous)
 
wwhitney said:
Stainless steel, of course, is ferrous. Would a non-magnetic alloy of stainless steel eliminate the heating due to magnetic hysteresis?

Cheers, Wayne
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304 stainless is very slightly magnetic, 316 stainless has negligible magnetic properties (both are austenitic). I believe the 400 series stainless steels are magnetic (martensitic). At home, the stainless steel front of the dishwasher is covered with all kinds of stickups for the kids. The refrigerator, on the other hand, would need epoxy to stick anything to the doors.
 
Adamjamma said:
It looks neat that way but back in eighties my boss made me carry a toy matchbox car with me... actually made a keychain of one... He had worked for a major manufacturer in both USA and Europe he found that One needed space between the conduits or you could have equipment problems. He insisted that the car was the perfect width to use for spacing wires above each other or for conduit spacing... he was boss so I did it.. never saw it in code, however, but still a GTO judge in my toolbox for that reason..plus car looks cool...lol
Click to expand...

Picture of car required :D
 
wwhitney said:
Stainless steel, of course, is ferrous. Would a non-magnetic alloy of stainless steel eliminate the heating due to magnetic hysteresis?

Cheers, Wayne
Click to expand...
The correct word in the code section should have been ferromagnetic rather than ferrous, but it is a common mistake.
 
GoldDigger said:
The correct word in the code section should have been ferromagnetic rather than ferrous, but it is a common mistake.
Click to expand...

Are you saying that this incorrect?

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 ar-
ranged 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.
Click to expand...
 
infinity said:
We've been running miles of Vitalink MC Cable for fire alarm and fire pump power. I've been told that according to the instructions you can space the cables like shown in the photo. I'm wondering, how this does not cause heating the surrounding ferrous metal by induction? Where is enters the steel enclosures a slot is cut between the individual KO's that complies with 300.20(B). Is it that a ferrous strut and strap about every 5' surrounding the cable is too small to cause any inductive heating?

View attachment 20898
Click to expand...

I'm assuming these are single conductor cables and hence the question. I think you really should contact Vitalink on this. I'm inclined to think this is an issue. I also believe that these should be bundled in a triangular fashion and all run thru 1 clamp. You would have to check but I think the listing (FHIT?) requires bundling when used on a trapeze.
Not sure of your application but in some cases where used for fire pump feeder downstream of a OCPD rated for locked rotor you might require a supplemental EGC rather than just rely in the jacket for EGC.
 
texie said:
I'm assuming these are single conductor cables and hence the question. I think you really should contact Vitalink on this. I'm inclined to think this is an issue. I also believe that these should be bundled in a triangular fashion and all run thru 1 clamp. You would have to check but I think the listing (FHIT?) requires bundling when used on a trapeze.
Not sure of your application but in some cases where used for fire pump feeder downstream of a OCPD rated for locked rotor you might require a supplemental EGC rather than just rely in the jacket for EGC.
Click to expand...

Yes, these are individual 350 kcmil conductors. According to the instructions it can be strapped in a triangular configuration with a single strap or individually as shown in the photo. I've been told that he individual method with some spacing in between each conductor allows for a higher ampacity since it's in free air. In this application that's not applicable because the conductors have been oversized considerably for voltage drop so either method would work.
 
infinity said:
Are you saying that this incorrect?
Click to expand...

Yes, I am. The heating problem results from magnetic hysteresis, not eddy currents, and so will occur with any ferromagnetic (magnetizable) material that encloses a significant current.
Not all iron alloys are ferromagnetic, but all are ferrous (containing iron.)
Not all ferromagnetic materials contain iron. Cobalt and nickel are mildly ferromagnetic, as is neodymium. (But "neodymium magnets" are actually an alloy of neodymium, iron, and boron).

To make physical sense and to apply to less common materials, the Code section should have cited ferromagnetic materials, not ferrous metals.
And, no, I have no intention of submitting public input on the subject. Feel free to notch up points if you are inclined. :)
 
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