EMT in concrete
- Thread starter darekelec
- Start date
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
Yes we use EMT straight from the supply house embedded in concrete all of the time. The fittings need to be listed as concrete tight. Typically compression type or set screw with tape.
herding_cats
Senior Member
- Location
- Kansas
- Occupation
- Mechanical Engineer
I avoid metallic EMT in any burial unless it's sched. 40 pipe. Use grey PVC if possible. Either way your call.
- Occupation
- Licensed Electrician
Any particular reason, or is it one of those things that you heard was bad and just accepted?
What other choices are there for electrical conduit?
herding_cats
Senior Member
- Location
- Kansas
- Occupation
- Mechanical Engineer
corrosion. PVC leak tight. Lime, cement and galvanized metal bad mix.
- Occupation
- Licensed Electrician
Why are the decks that concrete is poured on made of galvanized sheet metal then?
herding_cats
Senior Member
- Location
- Kansas
- Occupation
- Mechanical Engineer
cheap to build. planned obsolescence. Consider heat exchange coils made of galv and copper.
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
EMT embedded in concrete has it's shortcomings when it comes to durability but only where it enters and exits the pour and it may get damaged. Within the concrete there is no issue. Floor boxes are made of the same steel as the EMT. Steel rebar is within the concrete and that is not even galvanized.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Once the concrete sets up, the forms is no longer needed, so rotting in no longer an issue from a function standpoint. These forms are nit completely embedded so they may actually last for decades.
However, for conduit rotting can be a concern. Failed conduit no longer serves as a grounding path and collapsed sections can make removing and reinstalling conductors difficult to impossible. While not likely rotting embedded conduit could swell causing the to fracture.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
IIRC, there are metal pan systems for concrete slabs which are designed taking into account the bottom reinforcement provided by the pan. In an elevated dry application, there's no reason to expect the metal pan to corrode.
Cheers, Wayne
JohnE
Senior Member
- Location
- Milford, MA
Which is part of why the the expected life of a cast in place reinforced concrete building is 50 years. The rebar corrodes and expands, then starts deteriorating, which compromises the structural integrity of the reinforced concrete. (from the Simpson continuing ed programs, not my statement)
herding_cats
Senior Member
- Location
- Kansas
- Occupation
- Mechanical Engineer
What I'm getting at is when you introduce water there's trouble. You see rust failure right at the point where EMT exits concrete. I would recommend transitioning to sched. 40 galv where the conduit exits or could be exposed to air/water.
You did say above ground level which maybe people missed the first time. A slab poured on grade or foundation walls under the ground, those damp areas are different than a concrete pan decking ceiling/floor that is well above grade in a multi floor structure.
You probably aren't going to have corrosion issues with EMT in concrete that is ceiling/floor well above grade (e.g. pan decking above your head with concrete poured over it). But a concrete floor with dirt or gravel under it is probably going to be wet and thinly galvanized pipe like EMT could quickly corrode away. Rigid meal conduit with a thick galvanized coating will last much longer, but it can still disappear over time. PVC is best when you have concrete + water.
Changeover has to be accessible 300.15 (F)
Joethemechanic
Senior Member
- Location
- Hazleton Pa
- Occupation
- Electro-Mechanical Technician. Industrial machinery
Lift stations and wastewater plants are always full of conduit that's rotten off. Then you're trying to get where you got to go without having to saw up too much concrete
- Occupation
- Licensed Electrician
Not the same thing as a office building above ground level.