Question 1. I am trying to find a Code article or reference to the use of SE cable in conduit underground. Chapter 9 states that for multiconductor cables, you have to use the actual dimension. This is not a problem, because you just measure the outside diameter. My question is, Is USE cable listed for use in conduit underground? ? R.P.
Answer 1. The use of Type SE or USE in conduit either underground or aboveground is not prohibited by the NEC. However, neither of these cable types is listed for such use so the decision to accept or reject is up to the authority having jurisdiction (AHJ).
The following information may be helpful in considering such a decision. There are two serious concerns with this type of installation. The first is damage to the cable or individual conductors as they are pulled into the raceway. The other is the added resistance to heat dissipation. Both concerns can be addressed to some extent by using a conduit one size larger than required in Chapter 9. This reduces the friction of the pull, making it less likely that the conductors will be damaged during installation, and provides a larger air space to dissipate the heat buildup in the conductors under operating conditions.
In general, such an installation is poor practice and should not be permitted where there are more than two ninety-degree bends in the run of raceway or where the circuit is expected to run at full load (80 percent of rated ampacity) for any length of time. The sole advantage to running SE cables in conduit underground is the ability to replace them, if necessary, without excavating. Of course, the use of THHW conductors in conduit provides this same advantage with none of the drawbacks identified above and is probably more economical as well. ? T.E. Trainor, CMP-7
