15KV cables AA-BB-CC - Try Eng Forum

[KarlS]

I have installed (3) 15KV bushings on top of a metal building. THese bushings connect to the 15KV swgr inside by (2) per phase 500MCM shielded cables (MV-105). The run is short maybe 10ft. The SWGR is new Eaton arc resistant type. My drawings instructed the shop to install a 1/4" alum plate on top of the swgr and cut holes for the (3) bushings due to the megnetic induced heat effect of installing cables AA-BB-CC. I had no room in the chase with the stress cones for ABC-ABC.

You guessed it! They did not install the alum plate as instructed. The stress cones will not allow the cables to be pulled back thru the 3" bushngs. Now for Plan B. I know you must install alum or Glastic to stop the heating of the metal swgr top cover or plan B you can cut a slice from bushing to bushing in the metal to stop the effect. The system is rated for 1200A.

Has anyone installed cables like this and if so, how wide should the gab be that I intend to cut? I am thinking 1/2" to stop the circulating currents inducted in the swgr top cover.

My experiance is based on 16yrs as a MV swgr manufacture running cables within gear for custom applications. That however was several yrs ago and wanted to see what other exterior cable installers have done.

Thanks and look forward to your responses.

 

[bob]

Try as I may, I could not locate an article that could provide an answer to your question. Without any evidence I would think the 1/2" would work. I was in a class a while back and the instructor provided a sketch that he said it would correct your situation. I tried to make the sketch larger but could not. The conductor is #6 cu bare and it is looped thru each conduit hole and brought back into the cabinet and the ends are connected. This is a little different because it had a neutral opening. You may want to give it a try. You can click on the dwg to get a better view. Don't know how I ended up with 3 dwgs.

 

[don_resqcapt19]

It is my understanding that the width of the cut is not important. A single pass with a saw blade will do the job.

 

[KarlS]

AA-BB-CC

AA-BB-CC

Thanks for responses!

The cable is 500MCM and shielded with little space in the chase. That is why it's not ran ABC - ABC.

 

[RUWired]

Wouldn't the shielded cables cancel the induced heating effect??

 

[Smart $]

Wouldn't the shielded cables cancel the induced heating effect??

TTBOMK, passive shielding is ineffective at reducing 60Hz magnetic fields.