one of the one I find around here is people using Table 310.15(B)(6) on commercial installs, mainly 400 amp services with 500kcmil instead of 600kcmil, or 2/0 instead or 3.0 on a 200 amp service or feeder, mainly done by a residential electrician.
on a upgrade where they installed the new service panel at a new location using the old panel as a sub but not upgrading a 3-wire range or dryer feed to a 4 wire or relocating it to the new service panel.
NM in wet locations
boot legging grounds from the neutral (as mention very dangerous)
3-wire sub panel feeders
no electrodes at garages where fed by feeders
not grounding switch's when required
not sealing service conduit or others coming in from the outside where you have a difference of temp
forgetting to tighten setscrews on conduit fittings
more then one wire in a lug not listed for it
wall space violations, common is not including a fixed panel on French doors or sliders or railing partitions around stairs.
running URD or other non 310.13 listed conductors in a NEC covered install
set back box's mainly in cabinets without being flush
receptacle for dishwasher installed behind it.
NM sheathing cut short and not 1/4" inside of the box
dimmers on switch receptacles
no egc in FMC or LTMFC where circuit amperage exceeds the rating allowed for it, or 3/8"
fan rated box's where the fan is supported by it (not a violation if the fan bracket is supported to the joist and not the box)
using SABC to supply fixed in place appliances that are not allowed in 210 like dishwashers, disposals, ice makers, compactors.
splitting a 320 meter to two 200 amp main breaker panels not grouped 230.72
using overhead riser pipe to support TV antennas, cable drops, telephone drops.
no disconnect on water heaters
putting other loads on furnace circuits
underground UF cable barely 6" in the ground, many times just under the sod
using UF cable to feed pool equipment
mobile homes with bare copper EGC feeders.
not using expansion joints in PVC where it exits grade or on long runs
not derating conductors on roof tops
using vegetation such as trees to support overhead conductors
using ATS on generators not rated for load served
running LV conductors in line voltage conduits
running LV conductors in service panel (door bell transformer also installed in panel)
emergency lights and exits fed from dedicated circuit instead of put on with the lighting in area served.
receptacles above dropped ceilings with cords plugged in
NM used in places of assembly or with a stage
not maintaining 1 1/4" from stud edge without nail plates (hard to do where the wire enters a box)
wall space requirements for other walls in a kitchen 210.52
still trying to use dedicated receptacle in lew of GFCI as required now in the 2008
