For galvanized rigid steel, what is the recommended diameter in millimeters?

Study for the BICSI OSP Design Test. Prepare using multiple choice questions, with hints and explanations to enhance understanding. Succeed in your exam journey!

Conduit diameter is chosen to give enough pulling space for the cables while still fitting the installation and fittings comfortably. For galvanized rigid steel conduit, a size around 100 mm, basically a 4-inch class, provides a practical balance: it offers ample internal area for typical cable bundles and easier pulling, without the extra bulk and cost of a much larger diameter.

Why 103 mm is the best fit: it corresponds to the common practical size used in many OSP installations, giving enough internal volume for multiple conductors and reducing the risk of pulling resistance or damage during installation. The other options tend to be either undersized for typical cable pulls or unnecessarily large and costly for standard installations.

In short, 103 mm hits the sweet spot between enough space for cables and reasonable installation practicality.