Only two readers were able to correctly identify the violations with this rooftop installation. Dan Geske, president of Rural Electric Service, Inc., Fall Creek, Wis., and Charles J. Grew, a registered professional electrical engineer with Gannett Fleming, Inc., Camp Hill, Pa., were this month’s winners.

This photo shows an NM cable run through a rooftop exhaust vent for this apartment building’s laundry room dryers. The “warm and fuzzy” laundry lint is clearly visible in the vent and on the roof. Section 300.22(A) requires that no wiring systems of any type shall be installed in ducts used to transport dust, loose stock, or flammable vapors. Lint is dusty and highly combustible. In addition, 334.12(B)(4) does not permit NM cable to be installed in this outdoor wet location. There is also no disconnect for the motor. This is a violation of 430.102(B)(1) and (2) and the exception, because the exception would not be applicable in this case.