It was a really close call for the roofers who installed those long deck screws. In fact, it may be unseen from this view, but it's possible that some screws may have penetrated directly into the back of either box. Installation requirements in 300.4(E) of the 2011 NEC address this type of situation.

A cable, raceway, or box, installed in exposed or concealed locations under metal-corrugated sheet roof decking, shall be installed and supported so there is not less than 38 mm (1½ in.) measured from the lowest surface of the roof decking to the top of the cable, raceway, or box. A cable, raceway, or box shall not be installed in concealed locations in metal-corrugated, sheet decking–type roof."

The use of the long screws by the roofers when making repairs to the roof is the exact reason why boxes and wiring must be spaced down 1½ in. from the roof deck. The self-tapping type screws used here could have easily damaged the wiring in the EMT or boxes.

Although the exception in this section of the Code allows rigid metal conduit (RMC) or intermediate metal conduit (IMC) to be installed without the required spacing, there is no exception for the boxes. Therefore, if RMC or IMC were used, the boxes would still need to be spaced down 1½ in. from the roof decking.

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