Minimizing Inductive Heating by cutting slots

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tom baker

First Chief Moderator
Staff member
To minimize inductive heating where single conductors enter a metal enclosure slots can be cut between the separate openings.
Has anyone ever done this?
What would the AHJ say - would it violate the listing of the enclosure?

Here is the code section:

300.22(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
 

templdl

Senior Member
Location
Wisconsin
To minimize inductive heating where single conductors enter a metal enclosure slots can be cut between the separate openings.
Has anyone ever done this?
What would the AHJ say - would it violate the listing of the enclosure?

Here is the code section:

300.22(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

That?s and option but if you would cut a rectangular opening for all conductors and then fastened a sheet of fiberglass insulating material over the opening to the enclosure and then drilled your holes for the conductors through the insulating material that would solve your inductive heating issue. The name escapes me regarding what this method is called.
My factor made the mistake of running each phase conductor through its own grommet into the LV compartment of a pad mt transformer. To this day don't know what the heck they were thinking. Needless to say to have it corrected in the field was a bit expensive. It was embarrassing.
 
To minimize inductive heating where single conductors enter a metal enclosure slots can be cut between the separate openings.
Has anyone ever done this?
What would the AHJ say - would it violate the listing of the enclosure?

Here is the code section:

300.22(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

So how would one do that in anything other than NEMA 1 type enclosures and still maintain their rating?
 

iwire

Moderator
Staff member
Location
Massachusetts
That?s and option but if you would cut a rectangular opening for all conductors and then fastened a sheet of fiberglass insulating material over the opening to the enclosure and then drilled your holes for the conductors through the insulating material that would solve your inductive heating issue. .

In the field I doubt that reduction in enclosure wall would be allowed. Usually we use a brass or bronze plate.


MICableLahey009.jpg
 

renosteinke

Senior Member
Location
NE Arkansas
The copper tubing IS the wires. Each tube is a single conductor.

Induction equipment often has the wires inside water jackets to provide cooling. Lose the water flow, and a meltdown isn't far behind.
 

templdl

Senior Member
Location
Wisconsin
They are called Glan plates

They are called Glan plates

In the field I doubt that reduction in enclosure wall would be allowed. Usually we use a brass or bronze plate.


MICableLahey009.jpg

When it was necessary we used a glastic material for use as a gland plate similar to the attached picture.
 

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captainwireman

Senior Member
Location
USA, mostly.
The copper tubing IS the wires. Each tube is a single conductor.

Induction equipment often has the wires inside water jackets to provide cooling. Lose the water flow, and a meltdown isn't far behind.

This looks like MI cable. If it is, the conductors are inside a magnesium oxide material and the copper is the ground. We used it a lot at the North Slope oil fields. I would be most interested in learning about the style of wiring you are referring to. Can you give a link?
 

renosteinke

Senior Member
Location
NE Arkansas
Link? Not offhand. I do, though, have several components in our induction heating equipment with this stuff. It's all 'part of the appliance,' and not an actual wiring method that you assemble in bulk. Manufacturers of such equipment include Pillar and Elva.

There are wires inside, AND there is water being pumped through. In some instances, the exposed copper is itself the 'electrode,' with cooling water lines brazed to the copper plates.

It doesn't always seem to make sense, until you realize that this stuff often has 800+ amps being pushed through the equivalent of #10 wires. Toss in some truly wild waveforms and frequencies only a dog can hear, and there's a real heat problem.

I agree, though ... it does sort of look like MI.
 

captainwireman

Senior Member
Location
USA, mostly.
Link? Not offhand. I do, though, have several components in our induction heating equipment with this stuff. It's all 'part of the appliance,' and not an actual wiring method that you assemble in bulk. Manufacturers of such equipment include Pillar and Elva.

There are wires inside, AND there is water being pumped through. In some instances, the exposed copper is itself the 'electrode,' with cooling water lines brazed to the copper plates.

It doesn't always seem to make sense, until you realize that this stuff often has 800+ amps being pushed through the equivalent of #10 wires. Toss in some truly wild waveforms and frequencies only a dog can hear, and there's a real heat problem.

I agree, though ... it does sort of look like MI.

Thanks for the info. ...will check it out.
 

renosteinke

Senior Member
Location
NE Arkansas
It is MI? I stand corrected.

I haven't seen MI for decades ... yet I see induction stuff daily. I guess when you're a hammer, everything looks like a nail :D
 
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