Electrical run in Concrete slab

[Whiskeymike]

I’m going to be pouring a 25x40 slab off the back of the house for a covered Patio and curious about options for running electrical directly in the slab. I’ve been researching outdoor lighting and seeing solutions for embedding lights in the slab by core drilling after the fact. But it seems crazy not to lay the conduit and boxes necessary before the concrete is laid.

Is this a good idea? What conduit types are typically used? Would it only be used for the lighting in the floor? Or would it also be used to light from the ceiling down?

 

[Kevin Essiambre]

Most common conduit ran in concrete these days is Cor-line/smurf tube/ENT and PVC.

EMT used to be used a ton, but it's fallen out of favour in my parts because ENT is so easy to run and doesn't rust.

I've heard of rigid pipe being used, but that requires threading etc so it's not used unless it's required.

 

[Jim greengo]

I'd bury electrical PVC conduit in the ground before pouring the concrete.

 

[TurnipTruck]

I'd bury electrical PVC conduit in the ground before pouring the concrete.

THIS
Or your slab will crack where the conduit thins the concrete.

 

[u2slow]

I've probably installed miles of PVC and ENT in concrete slab in my electrical career. It is typically either run below slab, or at least below the top layer of rebar in the slab. Device/light boxes can to taped up and affixed inside concrete forms.

If can plan your setup thoroughly, and stick with your plan, its a good idea. Otherwise you're just burying money in concrete.

 

[830singleshot]

I built a 30x40 with under slab pvc stubbed up under the building girt. I made 12 home runs fanned out to all parts of the building perimeter. Brought all of them into a trough. It made for a first class job by myself. The only conduit overhead is for lights, a exhaust fan and water heater above my office. It looks so much better than a ton of conduits up and over to get power every place you want it. It will also save on wire cost as the runs are much shorter.
Run twice as many conduits as you think you need any make sure 20% are a larger size for 220v runs. PVC is cheap and you can't add more in the slab once you pour.
JMHO

 

[grounded-b]

THIS
Or your slab will crack where the conduit thins the concrete.

Not at all true. Like the previous poster said - run it on top of the vapor barrier and below the top re-bar. I have been a union electrician for 35+ years, and have run miles of PVC non-metallic conduit in slabs. Never have heard of a slab cracking, due to the PVC conduit. ( i suppose, if you only poured an inch or 2 of concrete, it might crack !! )

Steve

 

[alfredeneuman]

I make sure 20% are a larger size for 220v runs.

Why?

 

[grounded-b]

make sure 20% are a larger size for 220v runs. JMHO

I also was wondering why? If a circuit is 240V, it will use less current and therefore, smaller wire.

 

[59 wagon man]

Not at all true. Like the previous poster said - run it on top of the vapor barrier and below the top re-bar. I have been a union electrician for 35+ years, and have run miles of PVC non-metallic conduit in slabs. Never have heard of a slab cracking, due to the PVC conduit. ( i suppose, if you only poured an inch or 2 of concrete, it might crack !! )

Steve

though i'm not an electrician as a licensed plumber i can easily say if burying condiut in concrete will cause it to crack every condo in fla would have cracked floors. the only downside is that if you ever need to break the slab you can hit the conduit and cut a wire. if you can stay a foot below the concrete if that worries you

 

[haugy]

I built a 30x40 with under slab pvc stubbed up under the building girt. I made 12 home runs fanned out to all parts of the building perimeter. Brought all of them into a trough. It made for a first class job by myself. The only conduit overhead is for lights, a exhaust fan and water heater above my office. It looks so much better than a ton of conduits up and over to get power every place you want it. It will also save on wire cost as the runs are much shorter.
Run twice as many conduits as you think you need any make sure 20% are a larger size for 220v runs. PVC is cheap and you can't add more in the slab once you pour.
JMHO

Bringing this back up. Did your electrician (or you) just use fish tape and pull the runs through later, or did you try running string in them beforehand? Any tips on that part?

I'm at the prep part, and will be digging trenches next week to bury my conduit under my rock layer that's coming in. I'm starting to think I may just run them on top of the insulation & vapor barrier and then pour on top of them.

My floor will have radiant heat, so I'm a little concerned having water and electricity close to each other in case something somehow went wrong during pour. **** happens sometimes.

 

[rburke65]

I ran numerous 3/4” pvc conduits under the radiant heated floor and no problems. The heated fluid would have to get out of the pex tubing, into the conduit, and then into the electrical conductors. Don’t worry about it.

 

[78SC4X4]

You can easily run the string later by using a vacuum.

I ran the conduit just under the vapor barrier and insulation. There are some water/electrical separation requirements.

 

[830singleshot]

I used string and vacuum on some and fish tape on others and pulled everything by myself except 1 run. Some were easy and I struggled with others, but the end result is fantastic. Short runs, very clean and neat job.

 

[larry4406]

Be mindful of the number of elbows/sweeps in each run. Limit yourself to a total of 270 degrees of twist (three 90's). Beyond this the pull becomes much more difficult. Not sure if this is Code or just good practice but is what I was told by a commercial electrician.

 

[alfredeneuman]

Limit yourself to a total of 270 degrees of twist (three 90's). Beyond this the pull becomes much more difficult. Not sure if this is Code

Code allows up to 360 degrees between pull points

 

[wyliesdiesels]

I built a 30x40 with under slab pvc stubbed up under the building girt. I made 12 home runs fanned out to all parts of the building perimeter. Brought all of them into a trough. It made for a first class job by myself. The only conduit overhead is for lights, a exhaust fan and water heater above my office. It looks so much better than a ton of conduits up and over to get power every place you want it. It will also save on wire cost as the runs are much shorter.
Run twice as many conduits as you think you need any make sure 20% are a larger size for 220v runs. PVC is cheap and you can't add more in the slab once you pour.
JMHO

But why?

 

[mcbane]

But why?

Not everyone under NEC, and 220 volt suggests not a US install. Perhaps overseas electric code requires larger conduit at that voltage?

 

[wyliesdiesels]

Not everyone under NEC, and 220 volt suggests not a US install. Perhaps overseas electric code requires larger conduit at that voltage?

people in the US often say 220 though

 

[rburke65]

Because folks are under the assumption that a 220…240…241….whatever it takes….requires bigger wire and therefore larger conduits.

 

[rjn2649]

I would at least run 3/4 PVC. IF not too much more $$ maybe even 1" PVC. More room to ADD another circuit if NEEDED, Like if someone might want to put a 2xx outlet for a table saw, lathe, or welder Near a 1xx outlet.
** because I want to avoid the 110,120,220,240 thing.

 

[wyliesdiesels]

Not everyone under NEC, and 220 volt suggests not a US install. Perhaps overseas electric code requires larger conduit at that voltage?

that doesnt make sense though... a given load at 240v vs 120v, will use smaller wire because the amperage will be lower.... no need to run larger conduit for smaller wire.... thats just a waste of money and defies logic