PVC expansion couplings are seldom required in which type of installation?

PVC expansion couplings are seldom required in underground installations because the surrounding soil typically provides a degree of stability and support that mitigates the thermal expansion and contraction that occurs with changes in temperature. In many cases, the installation depth and the weight of the soil above can help to keep the conduit immobile, reducing the stress caused by expansion and contraction. This is in contrast to other installations, such as long conduit runs, where temperature fluctuations could lead to significant movement, making expansion couplings necessary to accommodate this. Likewise, outdoor installations might expose the conduits to temperature changes, prompting the need for expansion fittings to prevent damage. Therefore, underground installations are less likely to require these couplings.