25KV underground system

[Alim]

We are going to installed a 25KV three phase underground system which consists of two PVC ducts, one ducts will have main three single phase cables and another duct (spare) will have one spare cable. I am wondering if I need to attach any caps or something at the both ends of the spare cable for weather seal or can I keep them open? Your response or comments will be greatly appreciated.

The U/G cables run from riser pole to a three phase pad mounted transformer.

 

[charlie b]

I don't see this as a code issue, but rather a matter of good practices. I do wonder, however, what the purpose of the spare cable might be. You can't use it as a replacement for a damaged cable in the other duct, nor to parallel with a conductor in the other duct. I would have left that duct with nothing more than a pull string.

 

[Alim]

I don't see this as a code issue, but rather a matter of good practices. I do wonder, however, what the purpose of the spare cable might be. You can't use it as a replacement for a damaged cable in the other duct, nor to parallel with a conductor in the other duct. I would have left that duct with nothing more than a pull string.

Thanks. I think we can use the spare cable in case a single conductor out of the three is damaged. It may save some time for installing a new cable. Isn’t it?

 

[zbang]

If one pipe has ABC and the other has S, if C fails you could use S as a temporary although non-compliant patch*, but you can't pull the failed C out while AB are energized. Also, pulling the failed C might damage AB in the process.

* probably different lengths & impedance, etc Charlie can fill in that info better than I

 

[tom baker]

Yes please close end with pvc cap. Dont glue, just tap on with mallet. A pull string or better yet mule tape, tie to a foam plug stuffed in end of conduit

 

[Alim]

Yes please close end with pvc cap. Dont glue, just tap on with mallet. A pull string or better yet mule tape, tie to a foam plug stuffed in end of conduit

Yes ww will do that for the spare conduit but the question is about the spare cable

 

[charlie b]

If one pipe has ABC and the other has S, if C fails you could use S as a temporary although non-compliant patch*. . . .

I would not even use this as a "temporary patch," as "temporary" installations tend to linger on for years. It would be non-compliant because all conductors of the same circuit must be in the same conduit.

Following on to what zbang said, if one phase conductor fails, I see two possible choices. One is to remove all three conductors (while deenergized) and pull the good two along with a replacement for the bad one. Another is to pull three new conductors in the spare conduit (at which point, the one spare you mentioned putting in that conduit becomes useless).

My suggestion is either install a pull string or pull a complete set of conductors.

 

[electrofelon]

I would not even use this as a "temporary patch," as "temporary" installations tend to linger on for years. It would be non-compliant because all conductors of the same circuit must be in the same conduit.

Following on to what zbang said, if one phase conductor fails, I see two possible choices. One is to remove all three conductors (while deenergized) and pull the good two along with a replacement for the bad one. Another is to pull three new conductors in the spare conduit (at which point, the one spare you mentioned putting in that conduit becomes useless).

My suggestion is either install a pull string or pull a complete set of conductors.

any idea what the chances of collateral damage to the good conductors if one fails is? A friend of mine dug up a 15 KV class CN cable (not his fault, bad locate) and he didnt even know it, and it tripped out. But I could see it go the other way and turn the adjacent cables to chowder depending......

 

[Hv&Lv]

We are going to installed a 25KV three phase underground system which consists of two PVC ducts, one ducts will have main three single phase cables and another duct (spare) will have one spare cable. I am wondering if I need to attach any caps or something at the both ends of the spare cable for weather seal or can I keep them open? Your response or comments will be greatly appreciated.

The U/G cables run from riser pole to a three phase pad mounted transformer.

IF you use a spare cable it needs a parking bushing on both ends. My concern isn't code related. Why pull in one? You hinking one may go bad in conduit with all three in the same conduit? What if one cable blows out and takes another cable out? now you have two bad cables and only one spare.
as others have suggested, leave the spare conduit empty with nothing but a pull string in it.

 

[Alim]

IF you use a spare cable it needs a parking bushing on both ends. My concern isn't code related. Why pull in one? You hinking one may go bad in conduit with all three in the same conduit? What if one cable blows out and takes another cable out? now you have two bad cables and only one spare.
as others have suggested, leave the spare conduit empty with nothing but a pull string in it.

Thanks

 

[Alim]

I would not even use this as a "temporary patch," as "temporary" installations tend to linger on for years. It would be non-compliant because all conductors of the same circuit must be in the same conduit.

Following on to what zbang said, if one phase conductor fails, I see two possible choices. One is to remove all three conductors (while deenergized) and pull the good two along with a replacement for the bad one. Another is to pull three new conductors in the spare conduit (at which point, the one spare you mentioned putting in that conduit becomes useless).

My suggestion is either install a pull string or pull a complete set of conductors.

Thanks

 

[Alim]

Thanks all.. really appreciate it.. it helped me to take the right decision.