The sizing requirements for pull boxes, junction boxes, handhole enclosures, and conduit bodies exist to prevent conductor insulation damage. Proper conduit fill is critical for electrical safety, code compliance, and system performance. Overfilling conduits causes excessive heat buildup, difficult wire pulling, and potential insulation damage, while oversizing wastes money and installation space. What is the conduit? In short, it's. When installing insulated conductors of 4 AWG or larger, the minimum dimensions of pull or junction boxes installed in a raceway or cable run must comply with 314. Enter your information in the fields below and click “Calculate” at the bottom of the page. Keep on reading to learn: How to use this electrical junction box.