I understand the concept of installing a expansion fitting when installing pvc into an outside box for earth movement, but what if the pvc is secured in place by a concrete sidewalk. Do I have an arguement that the expansion fitting isn't needed?
Expansion Fittings 352.44 (B) Earth Movement
- Thread starter Rasbeary
- Start date
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
IMO your argument is sound. The raceway cannot be affected by earth settlement due to it being encased in concrete. Logic would then dictate that the expansion fitting would be doing nothing to mitigate the earth movement.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
What's the exact scenario?
Certainly you could have a concrete sidewalk running parallel to and not attached to a building, and if the sidewalk is on insufficiently compacted backfill or expansive soils, the sidewalk could move relative to the building. So if the conduit is secured to both the sidewalk and the building, you'd still need an expansion fitting.
But perhaps that's not the scenario you have.
Cheers, Wayne
DBill64
Member
- Location
- Washington, USA
- Occupation
- I&E Technician
You may also need expansion fittings on the PVC conduit run that leaves the concrete (if it is a fairly long run, or the area you are installing it in has severe temperature swings). This is to compensate for thermal expansion and contraction as per 352.44(A):
(A) Thermal Expansion and Contraction.
Expansion fittings for PVC conduit shall be provided to compensate for thermal expansion and contraction where the length change, in accordance with Table 352.44(A), is expected to be 6 mm (1⁄4 in.) or greater in a straight run between securely mounted items such as boxes, cabinets, elbows, or other conduit terminations.
The table 352.44(A) goes on to give expected amounts of expansion/contraction based on degrees of temperature change for a 100ft section of conduit. As long as the expected amount of expansion/contraction is less than 1/4" then you wouldn't need one.
(A) Thermal Expansion and Contraction.
Expansion fittings for PVC conduit shall be provided to compensate for thermal expansion and contraction where the length change, in accordance with Table 352.44(A), is expected to be 6 mm (1⁄4 in.) or greater in a straight run between securely mounted items such as boxes, cabinets, elbows, or other conduit terminations.
The table 352.44(A) goes on to give expected amounts of expansion/contraction based on degrees of temperature change for a 100ft section of conduit. As long as the expected amount of expansion/contraction is less than 1/4" then you wouldn't need one.
I did not think of this. They normally do not attach the sidewalk to the building slab or tilt wall.
These are service conduits on the rear of major retail buildings, not more than 3' exposed.
Up here in the north, the sidewalk would move up and down a little with frost heave, while the building foundation would stay pretty much fixed.
I don't know if you have that problem down there.
You could sleeve the conduit through the sidewalk so the sidewalk can move without pulling the conduit with it.
I'm not sure, but I suspect if a conduit goes straight down below the frost line before turning horizontal, it's probably not going to move much in relation to the building, even up here. (Assuming the conduit is not connected to a sidewalk or slab where it emerges).
I don't know if you have that problem down there.
You could sleeve the conduit through the sidewalk so the sidewalk can move without pulling the conduit with it.
I'm not sure, but I suspect if a conduit goes straight down below the frost line before turning horizontal, it's probably not going to move much in relation to the building, even up here. (Assuming the conduit is not connected to a sidewalk or slab where it emerges).