Rigid aluminum conduit

[amptech]

I am having a 30' x 50' building built for my electric shop. When I wire it I want to put as much of the conduit runs as possible in the slab. I would rather not use PCV as I think it looks ugly coming up out of the slab to boxes plus it can get broken easily when equipment and such gets bumped into it. I was planning on using 3/4" rigid aluminum and am interested in hearing feedback from you all on the pros/cons of doing so. I am planning on stubbing up and then back down all around the perimeter for GP receptacles and stubbing up to a box for the light switches and going on over-head from there for lights and OHD receptacles. All opinions are welcome. Thanks in advance.

 

[iwire]

If I recall Aluminum and concrete do not get along well together.

I would use PVC under the slab and use GRC 90s to stub up out of the concrete.

 

[peter d]

yeah, what Bob said is the standard practice around here. I never see PVC coming out of a slab unless it's going to be protected in some way (bottom of gear, under a piece of equipment, etc)

 

[celtic]

PVC in the dirt, RMC stubbing up.

 

[amptech]

For some reason I was under the impression that if you inserted a metallic section in an otherwise non-metallic run of raceway you had to bond both ends of the metallic section somehow if any part of the metallic section was exposed. I always use metallic 90s in a PVC run under a slab to avoid rope burn-thru but they are entirely below the slab. Am I misinformed here?

 

[iwire]

For some reason I was under the impression that if you inserted a metallic section in an otherwise non-metallic run of raceway you had to bond both ends of the metallic section somehow if any part of the metallic section was exposed.

The raceway has to be bonded at least once.

Only a raceway conting an GEC must be bonded at both ends.

Assuming you continue up with EMT or GRC to a metal box that is bonded with a 'wire' EGC you will be good to go.

 

[augie47]

(a) In the UL White Book (Section DYWV) it states "aluminum conduit used in concrete or in contact with the soil requires supplementary corrosion protecton"

(b) If you stubbed up in GRC and bonded it at the termination thas would be suffiecent, IMHO. Both ends (of that portion of the run) need not be bonded. Assuming you don't like RNMC, if you use RGC or EMT to your first box and bond there I would think that would be sufficent.
I believe the exception allowing GRC elbows requires them to be 24" below the surface in order to not be bonded, but I can't put my finger on that code reference.

(sorry I-wire, I was typing as you posted..didn't mean to step on you)

 

[220/221]

You could use PVC up to the finished floor with a female adapter. That way the concrete guys can finish right over it. You will still be able to locate them and screw your EMY connectors in.

I prefer to go PVC up thru the slab an inch or so (adapter depth) then adapt to EMT. That will eliminate any corrosion issues at floor level. PVC is pretty tough in the right conditions.


The sting/rope won't burn the 90's of you pre lube just a bit.

 

[John Valdes]

Use EMT. It looks great and is easy to work with. Lay the EMT on the rebar or wire mesh and use stands or another way to keep it inside the concrete, not on the dirt. Ty it with ty wire. You can buy concrete fittings for EMT.
If your not on the money with the stubs, two benders quickly and neatly adjust's them perfectly. Then EMT everything else. If your a good bender your shop electrical will be a thing of beauty.