Temporary Medium Voltage Cable

[philly]

I am working on a project where we are replacing existing 4.16kV outdoor Switchgear that is connected to overhead tubular bus. In order to install the new switchgear while the existing switchgear is still in service we will need to demo a portion of the the overhead bus. When demo'ing the over OH bus we will need to run temporary feeder cables from the existing switchgear to a portion of the remaining OH bus that will still be connected to loads.

My question.....When running temporary MV cables in an outdoor application like this are there any particular standards or Code sections that apply to this situation? For instance can cable be run on ground or does it have to be run in tray? Does cable tray have to have cover and be enclosed?

The existing switchgear had top entry bushings that are used for connection to OH bus and can be used for connection of temporary cable.

Is there a particular type of MV cable that is best suited for this temporary application? Temporary in this case will be 6-7 months.

I appreciate any feedback on this type of application.

 

[just the cowboy]

call Carr & Duff

call Carr & Duff

I am working on a project where we are replacing existing 4.16kV outdoor Switchgear that is connected to overhead tubular bus. In order to install the new switchgear while the existing switchgear is still in service we will need to demo a portion of the the overhead bus. When demo'ing the over OH bus we will need to run temporary feeder cables from the existing switchgear to a portion of the remaining OH bus that will still be connected to loads.

My question.....When running temporary MV cables in an outdoor application like this are there any particular standards or Code sections that apply to this situation? For instance can cable be run on ground or does it have to be run in tray? Does cable tray have to have cover and be enclosed?

The existing switchgear had top entry bushings that are used for connection to OH bus and can be used for connection of temporary cable.

Is there a particular type of MV cable that is best suited for this temporary application? Temporary in this case will be 6-7 months.

I appreciate any feedback on this type of application.

If you havn't done MV before I would not try it, it is something you don't guess at. In the Philly area Call Carr & Duff to do your temp service, great results from them for years.

 

[philly]

If you havn't done MV before I would not try it, it is something you don't guess at. In the Philly area Call Carr & Duff to do your temp service, great results from them for years.

I'm looking at this from an engineering perspective. I've done several MV projects before, just wanted to get some feedback on temporary installations like this with MV cables.

 

[Julius Right]

All requirements of NEC for permanent wiring shall apply to temporary wiring installations.
See: NEC/2014 Art.590 Temporary Installation ARTICLE 328 Medium Voltage Cable: Type MV and Art.300.37 Aboveground Wiring Methods.
NESC/2007 Rule 311. Installation and maintenance C.:For emergency installations, supply and communication cables may be laid directly on grade if they are guarded or otherwise located so that they do not unduly obstruct pedestrian or vehicular traffic and are appropriately marked. Supply cables operating above 600 V shall meet either Rule 230C or 350B.
Rule 350 General B. Cables operating above 600 V to ground shall have a continuous metallic shield, sheath, or concentric neutral that is effectively grounded.
EXCEPTION: At a splice or joint, the current path of the metallic shield, sheath, or neutral shall be made continuous but need not be concentric.

 

[steve66]

590 also limits temp. installations to 90 days. So this really needs to be installed with standard methods for a couple of reasons.

 

[philly]

300.37 states:

"In locations accessible to qualified persons only, exposed runs of Type MV cables, bare conductors, and bare bursars shall also be permitted"

Does this mean that type MV cable do not necessarily have to be installed in a raceway (conduit, cable tray, etc...) but can be exposed on ground or other means? I'm not suggesting this is the best way to do this, just trying to interpret this section of the code.

Also 328.10(3) and 328.10(6) both reference type MV cable that has an overall metallic sheath or armor and is identified as "MV" or "MC". Is this the same cable type as an MV-90 cable that is typically used which has a copper shield located under the cable jacket and insulation?

 

[iceworm]

590 also limits temp. installations to 90 days. So this really needs to be installed with standard methods for a couple of reasons.

The 90 day restriction only applies to "holiday decorative lighting and similar purposes". For construction is for as long as one needs. (590.3.A - 2017)

 

[iceworm]

... Is there a particular type of MV cable that is best suited for this temporary application? ....

I've done a few MV temporary feeders over the last few years. My preference is 5kV 3-c MCHL. 590.7 discusses guarding for wiring over 600V. Interesting this one didn't make the change to over 1000V. 590.4.J (Support) says you can't lay cables on the floor or the ground. I usually will put the cable up on a 2 x 6 laid on the floor (fastened with 2-hole clamps), or use treated wood sleepers (4 x 4, 6 x 6, 4 x 6) on 6' centers on the ground. Meets code - works well

... NESC/2007 Rule 311. ....

Philly - For my stuff, we are under the NEC. NESC does not apply. I don't know about yours. However, I highly suspect that if the NESC does apply - then the NEC does not.

ice

 

[steve66]

The 90 day restriction only applies to "holiday decorative lighting and similar purposes". For construction is for as long as one needs. (590.3.A - 2017)

That's right. I should have read it before I posted. For some reason that 90 day limit sticks in my head.

Still, I think there should be some reasonable limit to "temporary", and IMO, in most cases it should be a lot less than 90 days. I suppose the time limit is up to the AHJ.

 

[iceworm]

Limiting my discussion to NOT holiday lighting. Specifically, "Period of Construction"

... Still, I think there should be some reasonable limit to "temporary", and IMO, in most cases it should be a lot less than 90 days. ....

Okay. What would be your criteria? What number are you going to pick? How long does it take to build a house? How about a 20 story building? I'm liking, "As long as it takes."

... I suppose the time limit is up to the AHJ.

I hope not.

 

[steve66]

Limiting my discussion to NOT holiday lighting. Specifically, "Period of Construction"

Okay. What would be your criteria? What number are you going to pick? How long does it take to build a house? How about a 20 story building? I'm liking, "As long as it takes."

I hope not.

No, I wasn't suggesting any set time limit to cover all temporary installations. I'm just saying some consideration should be given to the need for the temporary installation, and any risks it might pose.

Your two examples both have definite goals and a definite end to construction. The owners and the contractors are normally all motivated to get the project finished, remove the temp, and get the final complete. So yes, I'd agree - As long as it takes.

I'm just saying I wouldn't want to be the Engineer or AHJ that approved having 4160 cables ran across the ground for 6 months. (And from the previous post, that wouldn't really be allowed anyway.)

I'm somewhat reading between the lines here, because the OP doesn't really say why its needed for 6-7 months, but it sounds a lot like "We'll just slap it in for now, and come back to fix it right when we don't have anything better to do, or when our budget gets a windfall." I don't think that was ever the intent of allowing temporary installations.

 

[iceworm]

Not discussing house ropers winding spliced and taped romex through a house while building. My discussion limited to industrial grade, 4160 and 480.

...I'm just saying I wouldn't want to be the Engineer or AHJ that approved having 4160 cables ran across the ground for 6 months. (And from the previous post, that wouldn't really be allowed anyway.) ....

Well, I have - a few longer than a year. And they looked safe to me. Consider reviewing a plan for temporary power should include: OC protection, ampacity, guarding, grounding, bonding.

Could the construction period have been shorter? Probably. As always, it comes down to money. Temporary power is in cause the company wants to stay in production. So the construction schedule has to work around the production needs. That usually costs plenty just by it's self.

Although one recommendation I would make to the OP is to have a documented inspection program, for all temp power, say every 90 days. Send someone out to see - is it still put in the way we originally put it in.

... I'm somewhat reading between the lines here, because the OP doesn't really say why its needed for 6-7 months, but it sounds a lot like "We'll just slap it in for now, and come back to fix it right when we don't have anything better to do, or when our budget gets a windfall." I don't think that was ever the intent of allowing temporary installations.

No, the OP did not say why they wanted 6 - 7 months. My between the lines said that was what the job will take. Nothing says your translation is just as good as mine - maybe better.

However:

NEC 590 does not really authorize "just slap it in" One still has to follow 240.100, 240.101. And then per 590.2.A, still have to follow all other requirements for permanent installations. And then there is the guarding per 590.7. And of course MCHL (my preferred for MV) has to follow 330 for specific uses, uses not permitted, securing and supporting. And I have on one occasion speced cable tray - so that brings in 392.

590 is pretty well written. It trades off installation requirements for requiring hard usage cord, extra guarding, extra GFCI.

Yes, it is somewhat disturbingly frightening that I agree with a code section.:jawdrop:

ice