A client requests a new 20A, 120V branch circuit to an outdoor shed. The circuit will be protected by a GFCI circuit breaker. The trench for the UF cable will be 12 inches deep. The shed is equipped with an outside receptacle. Under what specific condition, if any, is this burial depth permitted for a 120V, 20A branch circuit using UF cable?
- AOnly if the circuit is rated for 15A and protected by a GFCI.
- BThis burial depth is never permitted for UF cable.
- COnly if the circuit is 20A or less, 120V or less, GFCI protected, and installed under a concrete slab not exceeding 4 inches in thickness.
- DOnly if the circuit is 20A or less, 120V or less, GFCI protected, and installed within a dwelling unit's outdoor living area.
Show answer & explanationAnswer & explanation
Correct answer: C. Only if the circuit is 20A or less, 120V or less, GFCI protected, and installed under a concrete slab not exceeding 4 inches in thickness.
NEC Table 300.5, Note 4, permits a reduced burial depth of 12 inches for UF cable under specific conditions: the circuit is 120V or less, 20A or less, protected by a GFCI, and installed under a concrete slab not exceeding 4 inches in thickness and not subject to vehicular traffic. Without the concrete slab, the depth would be 18 or 24 inches depending on the type of protection.
Why the other options are wrong
- A. The 15A rating is not the sole condition; the circuit can be up to 20A.
- B. This statement is incorrect; specific exceptions exist for reduced burial depths.
- D. The 'dwelling unit's outdoor living area' is not a determining factor for this specific 12-inch depth exception; the concrete slab is key.
UF Cable Burial Depth Exception
The NEC provides specific exceptions to the standard burial depths for UF cable, allowing shallower installation under certain conditions, such as GFCI protection and installation under a concrete slab.
- Standard burial depth for 120V, 20A UF cable is 18 inches (without overcurrent protection at point of supply) or 24 inches for other conditions.
- GFCI protection is often a prerequisite for shallower burial depths.
- Installation under concrete slabs or streets can further reduce required depths.
Memory trick: UF cable in the ground, how deep must it be found? GFCI and slab, reduce the grab!