Underslab feeder

Status
Not open for further replies.
mshields

mshields

Senior Member
Location
Boston, MA
I'm putting a 1200A feeder from the main electrical room in a 2 story, 30,000 sq ft building to the main electrical room for one of it's tenants. I'm stuck with putting it under the slab due to conversations/agreements made before I cam on boards. The tenant happens to be an Ambulatory Surgery Center. I'm looking for input on how best to run this feeder under the slab. My inclination is to do it in direct burried RGS. Am I over doing it? underdoing it? What do you think?

Mike
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Schedule 40 PVC horizontally, transition to RGS as you come up through the slab continue the rest of the way with EMT.

Typically we run PVC underground and used RMC 90 degree sweeps to turn up through the slab.

This does two things, it makes it almost imposable for it to get damaged and makes sure we don't tug a pulling rope through the side of a PVC 90 sweep.
 
mshields

mshields

Senior Member
Location
Boston, MA
sold

sold

PVC with RGS sweeps - sounds good.

In answer to your question - why not PVC. I'm just a little paranoid about putting anything under the slab where you can't get at it if there is a problem. But I guess under the slab is a pretty safe place to be. And I assume your suggesting direct buried. No need for duct bank correct?

Thanks,

Mike
 
mshields

mshields

Senior Member
Location
Boston, MA
clarification please

clarification please

Dick,

I have overlaid structural drawings on mine to avoid such things, but I'm not installing it, I'm designing it. Other than designing the run to avoid these things, what would you suggest I do?

Thanks,

Mike
 
weressl

weressl

Esteemed Member
Location
Texas by the Gulf, geat crab, great shrimp
mshields said:
PVC with RGS sweeps - sounds good.

In answer to your question - why not PVC. I'm just a little paranoid about putting anything under the slab where you can't get at it if there is a problem. But I guess under the slab is a pretty safe place to be. And I assume your suggesting direct buried. No need for duct bank correct?

Thanks,

Mike
Click to expand...

Depends;

  • if any of the run is outside of the buildings, what traffic do you expect above the buried conduits, what earth movement can be expected, how stable is your soil, etc.
  • Often times you see another spare set of conduits run parallel, in case the cable blows up and burns.
  • If you are in an area where there is road salt expected, you may choose to emerge from the underground with a stainless steel conduit.
  • PVC to SS is OK but do not connect SS to RGS directly.
  • Fabricated large sweep bends made on a full length conduits are the best.
Of course any of the above are cost adders with benefits, so you may choose to discuss it with the Owner and let him intelligently decide what protection for the future he may choose.
 
Last edited:
ohmhead

ohmhead

Senior Member
Location
ORLANDO FLA
Well if its a new work you need to look at the shortest path between the start of run point and end point .

Meaning is plumbing in the way you need elevations you need underground plumbing drawns sanitary lines drain lines water lines gas line chiller lines sewer lines .

If your coming up in a spot you picked or need to rise up or cross overhead you need mechanical drawns duct work .

You also need Structural and Architectural drawns to keep your conduit install clear of them .

They have elevations we dont !

If its old work you have better know whats below slab now get old asbuilds or plans of stuff in the ground now existing pipe work below kinda important .

Find a route then look at all footers pads columns structural stuff plan your path to be short but watch out before you give a number you just might be in someones way double check this just some help here good luck .

Dont digg outside unless you call a locate on site !

If its in the city call it in trust me on this one !

If its a 1200 amp service and its short less then 250 feet or just two 90 elbows use PVC you will not burn up a pvc 90 at that distance ever .

If is more than that or more bends like three bends over 250 feet use rigid 90,s on pull side one side only .
If its a unprotected feeder you must enclose it in a fire safe chase rising up thur building !!!!!!
Have fun .
 
Last edited:
B

BJ Conner

Senior Member
Location
97006
ohmhead said:
Well if its a new work you need to look at the shortest path between the start of run point and end point .

Meaning is plumbing in the way you need elevations you need underground plumbing drawns sanitary lines drain lines water lines gas line chiller lines sewer lines .

If your coming up in a spot you picked or need to rise up or cross overhead you need mechanical drawns duct work .

You also need Structural and Architectural drawns to keep your conduit install clear of them .

They have elevations we dont !

If its old work you have better know whats below slab now get old asbuilds or plans of stuff in the ground now existing pipe work below kinda important .

Find a route then look at all footers pads columns structural stuff plan your path to be short but watch out before you give a number you just might be in someones way double check this just some help here good luck .

Dont digg outside unless you call a locate on site !

If its in the city call it in trust me on this one !

If its a 1200 amp service and its short less then 250 feet or just two 90 elbows use PVC you will not burn up a pvc 90 at that distance ever .

If is more than that or more bends like three bends over 250 feet use rigid 90,s on pull side one side only .
If its a unprotected feeder you must enclose it in a fire safe chase rising up thur building !!!!!!
Have fun .
Click to expand...

All very good to which I would add; " AS Built" and photograph the location of your duct bank. It could help you get more work in the future. It will build your reputation as a through and competent contractor and if rework of anything in the slab needs rework in the future you have the information.

As for rigid 90s - if doing something will burn up PVC 90s your not doing something right. A rope that's to small or the wrong material etc. Rope with a parallel core and proper lubricant will work fine.
 
D

dicklaxt

Senior Member
Certainly if you are given no choice in running below grade beams,interior of exterior, then any conduit location needs to be coordinated with the structural/civil engr and oft times grade beams have to be redesigned(bridged over conduit right of way)) to keep forces from being transferred to the conduits,,,,,,,PVC could fail and RGS could pull away on risers causing insulation damage and subsequent cable failure.If you are running parallel to a spread footing then you must stay out of a 45 degree "Cone of Deflection" from the bottom extremity of that footing.This may not be required by written text but repeating practice over the last 45 years has proven to me to be a often thought of and adherred to practice.

dick
 
R

Robert Hutcherson

Member
Location
Pembroke Pines,Florida
  1. Will the customer allow you to install GRC overhead from main electric room and up a chase to the the second floor?
  2. Can you run the conduit from main electric room up the outside of the building to the second floor?
  3. Just ideas that may or may not be viable
  4. Good luck.
 
Status
Not open for further replies.
Top