Minimum Conduit Spacing in Concrete Slab

[mull982]

Is there a minimum spacing that is required between conduits that stub up into a concrete slab? I know there are usually minimum when entering panels, enclosures, etc... to allow for bushing and locknuts, however in a concrete slab you do not have these fittings so I'm not sure there is even a minimum spacing required (conduits can be touching each other)

Does the NEC require any minimum separation in a slab, or is there a good accepted spacing practice?

Thanks

 

[infinity]

The NEC doesn't really care but conduit bunched together may weaken the slab so the building code might have something to say about it. On or current project the structural engineer inspecting before the pour has quite a bit to say about our deck piping and how it was installed lessening structural strength.

 

[mgookin]

Is there a minimum spacing that is required between conduits that stub up into a concrete slab? I know there are usually minimum when entering panels, enclosures, etc... to allow for bushing and locknuts, however in a concrete slab you do not have these fittings so I'm not sure there is even a minimum spacing required (conduits can be touching each other)

Does the NEC require any minimum separation in a slab, or is there a good accepted spacing practice?

Thanks

Every job is different from a structural and fireproofing perspective.

You don't want to choke the aggregate in the concrete mix nor do you want to interfere with required concrete cover at reinforcement locations; and you don't want them so close that fire collars can't be installed when necessary.

You haven't provided much information.

Infinity has answered with respect to the NEC but you also ask about "good accepted spacing practice" and from that perspective I'll just say each job is different.

For a slab on grade, have at it. For penetrations through elevated decks in a highrise, that's very different.

 

[mull982]

For a slab on grade, have at it. For penetrations through elevated decks in a highrise, that's very different.

The particular situation I am looking at is a slab on grade for an outdoor enclosure. I didn't think there were any minimum spacing requirements for a slab on grade but wasn't certain.

For slab on grade does the situation change any where there are several large conduits say 4" in a tight penetration window say 20" x 20"? Is it ok to but conduits up right against each other or should there be some minimum spacing? Concern is trying to fit required number of conduits in a penetration window.

 

[mgookin]

Have at it. You're fine.

 

[Fulthrotl]

The particular situation I am looking at is a slab on grade for an outdoor enclosure. I didn't think there were any minimum spacing requirements for a slab on grade but wasn't certain.

For slab on grade does the situation change any where there are several large conduits say 4" in a tight penetration window say 20" x 20"? Is it ok to but conduits up right against each other or should there be some minimum spacing? Concern is trying to fit required number of conduits in a penetration window.

1,200 amp gear..... just remember, you have to make it up, eventually.



when you pack a marshmallow into a piggy bank, you have to make it up before putting the guts back into the gear.

 

[Julius Right]

See[ for instance] Conduit Installation Guide[NV Energy]:
https://www.nvenergy.com/business/n...ectric_standards/images/SECTION_4/CD0001U.pdf

 

[mull982]

1,200 amp gear..... just remember, you have to make it up, eventually.



when you pack a marshmallow into a piggy bank, you have to make it up before putting the guts back into the gear.

Great Picture, thanks for sharing.

Those conduits appear to be 4"? Out of curiosity what is the size of that opening that these conduits are in? Just trying to get a relative idea for comparison.

 

[ron]

I also agree, for such a short portion of the run, you likely don't even need to worry about the raceway spacing for mutual heating (Neher McGrath Calculations or the equivalent NEC table)

The picture above is very neat, but I would hope the clamps would have been removed from the above application to avoid inductive heating of the individual phase conductors running through a circumferential ferrous material.

 

[K8MHZ]

1,200 amp gear..... just remember, you have to make it up, eventually.



when you pack a marshmallow into a piggy bank, you have to make it up before putting the guts back into the gear.

Are the clamps I am looking actually conduit strut straps?

 

[1964element]

That's my question also,is that unistrut

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[1964element]

You have those phased taped

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[electrofelon]

The picture above is very neat, but I would hope the clamps would have been removed from the above application to avoid inductive heating of the individual phase conductors running through a circumferential ferrous material.

I was thinking that as well. It does kinda look like aluminum strut though.....

 

[mull982]

With a 4" PVC conduit it appears from Table 9 of the NEC that the conduit O.D. is 4" and the I.D. is slightly smaller? What about factoring in the diameter of the conduit Bell End to make sure all Bell End's will fit?

For instance if I have a 18" wide opening can I say that I can line up (4) 4" conduits right next to each other and have a conduit width of 16" which will fit in the opening (simply multiply 4" conduit by # of conduits). Or is there usually a margin (maybe 1/2" or so for bell ends, etc...) factored into determining how many conduits can fit in a given slab area.

 

[mgookin]

With a 4" PVC conduit it appears from Table 9 of the NEC that the conduit O.D. is 4" and the I.D. is slightly smaller? What about factoring in the diameter of the conduit Bell End to make sure all Bell End's will fit?

For instance if I have a 18" wide opening can I say that I can line up (4) 4" conduits right next to each other and have a conduit width of 16" which will fit in the opening (simply multiply 4" conduit by # of conduits). Or is there usually a margin (maybe 1/2" or so for bell ends, etc...) factored into determining how many conduits can fit in a given slab area.

Nominal pipe size is inside diameter. Outside diameter is pipe size plus 2x wall thickness.

If you have bell ends, couplings, etc. you need space for them of course. Most manufacturers have detailed drawings available if you look for them.

 

[Fulthrotl]

Those conduits appear to be 4"? Out of curiosity what is the size of that opening that these conduits are in? Just trying to get a relative idea for comparison.

they are 4" schedule 40 pvc

The picture above is very neat, but I would hope the clamps would have been removed from the above application to avoid inductive heating of the individual phase conductors running through a circumferential ferrous material.

the strut is aluminum. non ferrous, no closed loop for induction heating. straps are still there.

Are the clamps I am looking actually conduit strut straps?

nope. they have a neroprene insert, and are available in lots of sizes.
none of the conductors insulation in that panel contacts metal directly.
http://www.hydra-zorb.com/

That's my question also,is that unistrut

aluminum strut. nobody had fiberglass in stock, and lead time was excessive.
my wholesale house stocks aluminum strut.

You have those phased taped

i phased them after termination. the way they were laced up, it was pretty easy
to identify them.

I was thinking that as well. It does kinda look like aluminum strut though.....

yep.

With a 4" PVC conduit it appears from Table 9 of the NEC that the conduit O.D. is 4" and the I.D. is slightly smaller? What about factoring in the diameter of the conduit Bell End to make sure all Bell End's will fit?

allow 4 1/2" per pipe. it'll fit. OD on a 4" schedule 40 ASTM pipe is 4.5"

when i formed up the pad for the gear, i took a 4x8 sheet of plywood, and cut a hole in it the exact size
of the inside of the gear... put the cutout in the gear to make sure.

then i screwed the plywood to the top of the form, so there were no oopsies.
installed, cut put bell mouths on, pulled mule tape, and taped up the
conduits, then pulled the plywood off the form and poured it.

built a rack down in the ditch to hold the conduits so nothing moved.
if you look at the inside of the gear, there is 1/16" extra on the width
to play with. the gaps in the pipe in the grouping had to happen to get
the stuff to fit. pipes crossed each other.

 

[1964element]

Nice I learned something today

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[packersparky]

The NEC doesn't really care but conduit bunched together may weaken the slab so the building code might have something to say about it. On or current project the structural engineer inspecting before the pour has quite a bit to say about our deck piping and how it was installed lessening structural strength.

What about 310.15(B)(3)(b)? (2011 NEC)

 

[K8MHZ]

Nice I learned something today

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Me too!

Thanks Fulthrotl!

 

[don_resqcapt19]

What about 310.15(B)(3)(b)? (2011 NEC)

I submitted a proposal on that issue a number of code cycles ago. The CMPs response was that if you had enough space to accommodate the conduit fittings such as locknuts, bushings or couplings you had enough space.