replacing freestanding switchboard

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malachi constant

Senior Member
Location
Minneapolis
We're looking at replacing a freestanding main entrance switchboard (2000A, 208V/3p/4w, if it matters). The existing switchboard contains one incoming/main section, and three distribution sections - the new one will be basically the same. For a number of good reasons we are looking at locating the new switchboard in the same room, about eight feet away, parallel to the existing equipment, on an exterior wall. At first glance this will be a very clean installation and switchover, but looking closer there is one detail that is bugging me. There are very few conduits coming out of the top of the equipment, and as we can see the back, front and sides we have every reason to believe most of the conduits are fed from below. We are on grade, there is no crawl space or basement below. We do not want to leave this in place as a massive pullbox - we want it gone.

My first thought was to write up the contract documents to state contractor shall cut and trench the floor from old gear to new, and intercept and extend buried conduits as required. Unfortunately the conductors will almost certainly not be long enough to reach the new switchboard. So can I have the contractor cut a pull box into the floor under (or immediately adjacent to) where the switchboard presently sits, and then pipe from there underslab over to the new switchboard? Is this a bad solution? What would you do?

Thanks!
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
We're looking at replacing a freestanding main entrance switchboard (2000A, 208V/3p/4w, if it matters). The existing switchboard contains one incoming/main section, and three distribution sections - the new one will be basically the same. For a number of good reasons we are looking at locating the new switchboard in the same room, about eight feet away, parallel to the existing equipment, on an exterior wall. At first glance this will be a very clean installation and switchover, but looking closer there is one detail that is bugging me. There are very few conduits coming out of the top of the equipment, and as we can see the back, front and sides we have every reason to believe most of the conduits are fed from below. We are on grade, there is no crawl space or basement below. We do not want to leave this in place as a massive pullbox - we want it gone.

My first thought was to write up the contract documents to state contractor shall cut and trench the floor from old gear to new, and intercept and extend buried conduits as required. Unfortunately the conductors will almost certainly not be long enough to reach the new switchboard. So can I have the contractor cut a pull box into the floor under (or immediately adjacent to) where the switchboard presently sits, and then pipe from there underslab over to the new switchboard? Is this a bad solution? What would you do?

Thanks!

I can think of a number of good reasons why every attempt should be made to put the new gear where the old was. I am guessing that the biggest good reason not to is the down time for the swap. Get a good EC and you should be able to do that work over a weekend with proper planning. Cutting the box in the ground is probably going to take as long and cost more. But, yes you can do it. Without a lot of thought, I start to think down time may not be your "good reason" because the only way you avoid down time is to leave the old gear as a junction box.
 

JoeStillman

Senior Member
Location
West Chester, PA
Intercepting conduits below the floor is a nasty bit of business. Can your loads be shut down long enough to do the work?

I would rent a substation and back-feed the loads with temporary wiring, then locate the new board on top of where the old one was and refeed the old cables.

If you can't live with the old board as a splice box, could you live with a smaller box in the same place? There might even be enough room to put a box inside each switchboard section. if not, you could remove the old board one section at a time, replacing each section with a smaller splice box. It depends on what kind of old gear you have. Use temporary wiring as above to do it in phases.
 

malachi constant

Senior Member
Location
Minneapolis
The "lots of good reasons" are:
* minimize downtime (which with the underfloor conduits makes this a moot point)
* clean up the room - get the equipment out of the middle where it wastes the longest wall. Though to be honest moving it to one wall will somewhat negate the wall that will now be freed up.
* the existing gear is fed from the utility via concrete encased conductors running right across the floor. So as soon as you walk into the room you have a significant trip hazard.
* the existing gear faces a wall, and is exactly 36" from face of gear to face of wall. In most opinions this is legal, but certainly not optimal when there is so much other space in the room. (I guess it's not legal when you consider there is only the one exit.)

Moving the gear solves all of these. Or on its face it did, until the underfloor conduits were realized.

As for the reason, there is money in the budget to do upgrade old electrical equipment, and this stuff is 50 years old...presto, it gets changed.

I'll probably replace it in place, but mirror it 180 degrees to open to the main part of the room, giving us twice the clearance and making one door acceptable again. I will likely have the utility feeder trenched in instead of concrete-encased to eliminate the tripping hazard.

Any other thoughts let me know. Thanks all!
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
The "lots of good reasons" are:
* minimize downtime (which with the underfloor conduits makes this a moot point)
* clean up the room - get the equipment out of the middle where it wastes the longest wall. Though to be honest moving it to one wall will somewhat negate the wall that will now be freed up.
* the existing gear is fed from the utility via concrete encased conductors running right across the floor. So as soon as you walk into the room you have a significant trip hazard.
* the existing gear faces a wall, and is exactly 36" from face of gear to face of wall. In most opinions this is legal, but certainly not optimal when there is so much other space in the room. (I guess it's not legal when you consider there is only the one exit.)

Moving the gear solves all of these. Or on its face it did, until the underfloor conduits were realized.

As for the reason, there is money in the budget to do upgrade old electrical equipment, and this stuff is 50 years old...presto, it gets changed.

I'll probably replace it in place, but mirror it 180 degrees to open to the main part of the room, giving us twice the clearance and making one door acceptable again. I will likely have the utility feeder trenched in instead of concrete-encased to eliminate the tripping hazard.

Any other thoughts let me know. Thanks all!

That sounds good from the information you gave. There are a couple of things I think about regarding the feeder. Is there a way you can set your first section where there is no gear now, allowing you to do your new feeder and section before the shutdown? I am thinking you are installing a new service lateral. Is the service lateral done by the EC or the Utility company? Draw a picture of the room layout and the direction the feed comes from and the experience represented on this site will surely offer you a good solution. PS, don't forget to require meggering of the existing feeders!
 

malachi constant

Senior Member
Location
Minneapolis
That sounds good from the information you gave. There are a couple of things I think about regarding the feeder. Is there a way you can set your first section where there is no gear now, allowing you to do your new feeder and section before the shutdown? I am thinking you are installing a new service lateral. Is the service lateral done by the EC or the Utility company? Draw a picture of the room layout and the direction the feed comes from and the experience represented on this site will surely offer you a good solution. PS, don't forget to require meggering of the existing feeders!

I could see putting the service disconnect on the exterior wall, then piping over to where the existing switchboard is (was) to feed the new switches. I think that's a great idea.

The service lateral (I assume you are referring to the utility transformer secondaries) is by the EC. I want to replace these from transformer to where they hit the service disconnect.

Regarding meggering:
* This is a high school. Would you all consider it a good use of resources to megger the distribution feeders that go to panels and large motors? School is about 50 years old, and we are replacing a number of these panels in place (keep enclosure, strip out the guts and replace with new lugs/breakers).
* I assume you can do this from one end of the cable - don't need to chase down access to both ends.
* Only once, like ten years ago, have I worked with an engineer who asked for meggering, and that was on a medium voltage cable. Where I can find some good verbiage to put in some contract documents? We're looking at a 208V system here.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
I could see putting the service disconnect on the exterior wall, then piping over to where the existing switchboard is (was) to feed the new switches. I think that's a great idea.

The service lateral (I assume you are referring to the utility transformer secondaries) is by the EC. I want to replace these from transformer to where they hit the service disconnect.

Regarding meggering:
* This is a high school. Would you all consider it a good use of resources to megger the distribution feeders that go to panels and large motors? School is about 50 years old, and we are replacing a number of these panels in place (keep enclosure, strip out the guts and replace with new lugs/breakers).
* I assume you can do this from one end of the cable - don't need to chase down access to both ends.
* Only once, like ten years ago, have I worked with an engineer who asked for meggering, and that was on a medium voltage cable. Where I can find some good verbiage to put in some contract documents? We're looking at a 208V system here.


If you do that with the disconnect outside that work can all be done before shutdown.

Yes I was referring to the Secondary conductors, different Utilities deal with this differently, for example California under PG and E it is conduit by EC, wire by PG and E, and in Florida it is on the Contractor.

Regarding meggering I can't shout YESSSSSSSSSSSSSSSS! loud enough!

With old wiring it serves two purposes, it verifies that the installer of the new gear didn't mess it up, and it verifies the integrity of the insulation throughout the system. In actuality the other end does need to be found, because the wire needs to be isolated to properly megger it. By this, you can go to a sub panel and turn off the main, or the breakers and that is the isolation that is needed. Oh, it will also tell whether you have a secondary (illegal) ground bond. I can't believe you have only had one EE require meggering. Most of the specifications I have require meggering of at least all feeders before energizing.

Regarding verbage, I don't know, but I would think you could steal it from most specs that are out there, or even get some sort of spec from a company that manufactures the meters.
 

zog

Senior Member
Location
Charlotte, NC
* Only once, like ten years ago, have I worked with an engineer who asked for meggering, and that was on a medium voltage cable. Where I can find some good verbiage to put in some contract documents? We're looking at a 208V system here.

Very suprising, the most basic and standard new instalation test. On a side note, Meggering a MV cable won't tell you much.
 

zog

Senior Member
Location
Charlotte, NC
As for the reason, there is money in the budget to do upgrade old electrical equipment, and this stuff is 50 years old...presto, it gets changed.

Waste of funds if you are just replacing due to age. Compare the build quality of the new disposable equipment you get today to the 50 year old stuff. 50 years is the average age of switchgear in nuclear plants, they just maintain them correctly, but they are much more reliable.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
Very suprising, the most basic and standard new instalation test. On a side note, Meggering a MV cable won't tell you much.

I forgot to pick up on this. Usually hi-pot testing is required for MV cable. Of course, technically, you are still looking for megohms of resistance the input is just higher.
 

zog

Senior Member
Location
Charlotte, NC
I forgot to pick up on this. Usually hi-pot testing is required for MV cable. Of course, technically, you are still looking for megohms of resistance the input is just higher.

DC hipot testing is considered a destructive test on MV cables, specifically ones in service for 5 or more years. IEEE/ANSI/NETA/ICEA have all revised thier standards to reflect this. Plus a DC hipot will only find gross installation errors and will miss the majority of cable defects.
 

malachi constant

Senior Member
Location
Minneapolis
I forgot to pick up on this. Usually hi-pot testing is required for MV cable. Of course, technically, you are still looking for megohms of resistance the input is just higher.

That could have been what it was. I had probably been out of school all of six months, who knows what the heck they were doing. I didn't get to spec it, watch it, read the reports, etc. Just remember him telling me about it, I'm pretty sure it was MV. Hi-pot for MV. Good to know.

Regarding replacing the equipment being a waste of money. The client was allocated funds earmarked for specific tasks. When the people controlling the purse strings offer you money to replace 50 year old equipment, you take it, lest it be 50 more years before the opportunity rises again. Plus, this is not a sophisticated client that ever exercises or tests their switchboards, so we don't have as much certainty about the operability of the equipment that you would in a more industrialized facility. But your (zog's) point is noted.

As I mentioned before, the five or six more experienced EE's I've had the pleasure to work with have not gone the meggering route. I wrote the specs for most of those guys and when it came to that option at most they would say "leave it in, but don't make them submit it - they won't test it, but we'll at least be able to (coyly) ask for the reports should there be an issue." And that's at most - usually they would say take it out. Most of the stuff we do is K-12, municipal (police/fire stations/city halls/courthouses/etc), projects like that. Do you think it is a given that new installations should always be tested? How often is a failure found in a newly pulled cable? How often in an untested cable does an event occur? How far down the riser do you test cables - just the bigger distribution equipment? How small/non-critical of a motor do you test? Do you test 100A feeders to lighting/receptacle panels?

As always thanks for the input!
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
That could have been what it was. I had probably been out of school all of six months, who knows what the heck they were doing. I didn't get to spec it, watch it, read the reports, etc. Just remember him telling me about it, I'm pretty sure it was MV. Hi-pot for MV. Good to know.

Regarding replacing the equipment being a waste of money. The client was allocated funds earmarked for specific tasks. When the people controlling the purse strings offer you money to replace 50 year old equipment, you take it, lest it be 50 more years before the opportunity rises again. Plus, this is not a sophisticated client that ever exercises or tests their switchboards, so we don't have as much certainty about the operability of the equipment that you would in a more industrialized facility. But your (zog's) point is noted.

As I mentioned before, the five or six more experienced EE's I've had the pleasure to work with have not gone the meggering route. I wrote the specs for most of those guys and when it came to that option at most they would say "leave it in, but don't make them submit it - they won't test it, but we'll at least be able to (coyly) ask for the reports should there be an issue." And that's at most - usually they would say take it out. Most of the stuff we do is K-12, municipal (police/fire stations/city halls/courthouses/etc), projects like that. Do you think it is a given that new installations should always be tested? How often is a failure found in a newly pulled cable? How often in an untested cable does an event occur? How far down the riser do you test cables - just the bigger distribution equipment? How small/non-critical of a motor do you test? Do you test 100A feeders to lighting/receptacle panels?

As always thanks for the input!

It will be interesting what others says, but for me, meggering the feeders is a no brainer. I don't like to turn on a breaker and have it trip, especially with a bang. For me, panels, motors and large equipment feeders (#2 and bigger) is OK, but I am just an electrician. I have seen wire come in from the supply house with a small gouge in the insulation and bare wire exposed. In this case it just happened to be a run I was "flaking" out before pulling. Had it gone directly in the conduit I probably wouldn't have seen it.
 
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