hollow core precast planks

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DaveBowden

Senior Member
Location
St Petersburg FL
I'm trying to bid a new house that is being built with prestressed hollow core planks for the flooring system for the first and second floors of living space. The bottom of the first floor plank will be the ceiling for the garage area.
My problem is in over 40 years of wiring here, I've never worked on one of these types of jobs and I sure would appreciate some advice.
From what I can discern from the prints, the garage ceiling will not be covered and everything will have to be surface piped. The only glaring problem I see with this are the 3 recessed cans they drew on the outside porch ceiling. I figure the other lights, ceiling fans, and receptacles will all be all right in conduit. It might take a little extra time to make sure it looks good when its finished, but we can do that.
As far as the first floor of living space, would standard practice involve piping on the garage ceiling and using an LB for stuff like the kitchen island?
The plans call for 2 floor receptacles. Can they be core drilled from the top and fed thru the hollow channels in the slab?
How hard is it to run wiring thru the channels in the slabs usually?
Finally, are there any special code requirements for the NM romex if it is run in the hollow cores?
Thanks in advance for any and all help
 
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DaveBowden

Senior Member
Location
St Petersburg FL
I'll try that, but I thought with the wealth of knowlege on this site someone would have worked with this before. I also thought it would be more likely to get electrical code questions answered here than on a concrete manufacturers web site.
 
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GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
DaveBowden said:
I'll try that, but I thought with the wealth of knowlege on this site someone would have worked with this before. I also thought it would be more likely to get electrical code questions answered here than on a concrete manufacturers web site.
Click to expand...

There are at least two potential issues here:
1. Can NM be run inside the pre-existing channels in the precast planks? The answer to this will depend on whether the rules for direct contact with raw concrete apply or whether this is just considered another type of chase.
2. Can you drill the core holes into the plank without affecting its mechanical integrity? That is a question for the manufacturer and the NEC will not help you at all. :)
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
It may be entirely different there, but I have inspected two homes here that have that construction and the building inspector required all contractors to have an engineered letter approving the size and location on any hole.
 
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__dan

Senior Member
DaveBowden said:
I'm trying to bid a new house that is being built with prestressed hollow core planks for the flooring system for the first and second floors of living space. The bottom of the first floor plank will be the ceiling for the garage area.
My problem is in over 40 years of wiring here, I've never worked on one of these types of jobs and I sure would appreciate some advice.
From what I can discern from the prints, the garage ceiling will not be covered and everything will have to be surface piped. The only glaring problem I see with this are the 3 recessed cans they drew on the outside porch ceiling. I figure the other lights, ceiling fans, and receptacles will all be all right in conduit. It might take a little extra time to make sure it looks good when its finished, but we can do that.
As far as the first floor of living space, would standard practice involve piping on the garage ceiling and using an LB for stuff like the kitchen island?
The plans call for 2 floor receptacles. Can they be core drilled from the top and fed thru the hollow channels in the slab?
How hard is it to run wiring thru the channels in the slabs usually?
Finally, are there any special code requirements for the NM romex if it is run in the hollow cores?
Thanks in advance for any and all help
Click to expand...

Check with the manufacturer for their affirmation once you have a plan and proposed method. NM will probably meet code run in the hollow core (don't quote me) with the usual caveats about protection from sharp edges and such. Commercial, I would automatically think about running MC, up an in from steel wall studs, even if NM is allowed. I would look it up or someone else will speak.

The planks are prestressed with high carbon steel cables in the solid. I've run a lot of MC in the hollows. There is usually a perpindicular wall allowing a spot to pop up into the hollow then run horizontally to a recessed 3" x 2" box (narrow side aligned with the run of the hollow). I have a fast method for popping the 3"x 2" opening. Mark it, make sure it's in the hollow, drill the four corners with a small hammerdrill (3/8" maybe), drill out the two device yoke screw locations, and pop the thin cement out with a small hammer. You can then usually fish from the opening at the up wall to the ceiling box location. The planks are not always hollow, sometimes they have a pebble fill. Plan your method then ask the manufacturer's approval, before cutting or drilling their plank and making it your plank. If you see the exposed steel cable, do not damage it or touch it.

Pretty sure recessed cans in the plank are out. I would not cut an opening larger that for the 3 x 2 switchbox. Recess the wiring and surface mount the fixture. Consider MC for difficult pulls in the hollow. The floor boxes I would not recess, but concealed MC run in the hollow to a tombstone outlet may be OK (owner's discretion). Consider that if you try to do a flush mounted, poke through device, the plank factory may not allow the width of coring necessary to accomodate a flush, poke through system.

I've seen guys do real trash work running NM in the walls, then sleeving it with wiremold surface mounted across the planks. I would run MC in the hollow fully concealed.
 
J

John120/240

Senior Member
Location
Olathe, Kansas
I took a look at Oldcastle precast plank web site. You mention can lights on the front porch. How is that going to work ? Will the

carpenters fir down to accommodate the cans ? On interior ceilings will you be using exposed EMT ? What type of interior walls will the

home have ? A different construction method for residential that we have not seen yet, hence the questions.
 
D

DaveBowden

Senior Member
Location
St Petersburg FL
New for me too - hence the questions.
I don't see them getting the cans unless they frame it down. Most interior walls are standard steel stud. Outsid walls are block up both floors with rigid insulation and then metal furring channel. The ceilings will have to be dropped for ductwork at least.
I'm going to try to meet the builder tomorrow to get some answers.
Prints have no load calculations except for the a.c. equipment. Nothing about the pool pump or the boat lift that are there already. No interior wall sectins to answer my questions about how its framed. 4 pages of prints for mechanical but only 1 page for electrical with the ground floor, 1st floor, 2nd floor, and roof deck all on that page. No spec for devices, etc. They leave a lot to be desired.
Over 6000 sq feet total - only about 3500 sq feet conditioned - but I still don't see the 200 amp service the builder said it gets as being enough. Elevator,too. Only gas is the fireplace and the pool heater.
We'll see.
 
M

mkgrady

Senior Member
Location
Massachusetts
We used to run bx through those channells. At steel stud walls we would knock a hole through the top plate and into the channell. We used 4 pound hammers and bull point chisels. Three swings of the hammer at the same spot would soften the concrete. After that the chisel went through the metal top plate like nothing. Push a snake to wherever and tie on your cable.
 
hbiss

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
If the ceilings are dropped how much cable do you really need to run in the cores? I can see through holes for feeders and home runs but that's about it. What would you do if this was solid instead of hollow core?

-Hal
 
Fulthrotl

Fulthrotl

~Autocorrect is My Worst Enema.~
Location
HB, CA (19 Hrs. 22 Min. from Winged Horses)
Occupation
E
DaveBowden said:
New for me too - hence the questions.
I don't see them getting the cans unless they frame it down. Most interior walls are standard steel stud. Outsid walls are block up both floors with rigid insulation and then metal furring channel. The ceilings will have to be dropped for ductwork at least.
I'm going to try to meet the builder tomorrow to get some answers.
Prints have no load calculations except for the a.c. equipment. Nothing about the pool pump or the boat lift that are there already. No interior wall sectins to answer my questions about how its framed. 4 pages of prints for mechanical but only 1 page for electrical with the ground floor, 1st floor, 2nd floor, and roof deck all on that page. No spec for devices, etc. They leave a lot to be desired.
Over 6000 sq feet total - only about 3500 sq feet conditioned - but I still don't see the 200 amp service the builder said it gets as being enough. Elevator,too. Only gas is the fireplace and the pool heater.
We'll see.
Click to expand...

if you want a can light in that stuff.... use glimpse.... it's a LED can light
retrofit that will fit 6" cans, 5" cans..... and 4sd boxes.... :happyyes:
$40 each, home dipsnit sells them, or you can get them directly from the
manufacturer, in florida.

festool makes some amazing blades for their pendulum jigsaws, and i've
cut thru 2" face brick to put 4sd boxes in columns with it. perfectly clean cuts.

i've not had the thrill of running in the voids on this type of post tensioned beam,
but it seems to me it'd be about like cutting into post tensioned slabs...

i've had to anchor stuff to them tho, and what worked for me was looking
for any metal with a good stud finder... i used the milwualkee one that is on
rollers.... and keeping away from anything metal in the beam.. dunno
if hitting one of those cables is anything like a post tensioned slab, and
intend to stay ignorant of those details.
 
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