Ten Common Residential Violations of the NEC, other than nail plates
1. Box fill: The most common violation that I write up. Briefly, hot and every neutral (other than pigtails) are counted as 1 conductor. All of the equipment grounds are added together and counted as one conductor. Any device that terminates in the box is counted as two conductors. 14 AWG=2.00 cubic inches, 12 AWG=2.25 cubic inches. A typical violation would be (3) 12-2 NM cables and a device (switch or receptacle) in an 18 cubic inch box. This would be a total of (9) 2.25 cubic inch conductors, totaling 20.25 cubic inches. [314.16]
2. At least one 15 or 20 amp, 125 volt receptacle must be installed within 25? of an air conditioner. [210.63]
3. At least 1/4? of NM cable sheathing must extend into every device box. [314.17(C)]
4. Metal raceways used as service lateral conduits must be reamed to remove sharp edges. Have you ever reached into a conduit to check this and came up bleeding? I have

[342.28, 344.28].
5. A neutral to ground connection is not allowed downstream of the service disconnect?check for green screws in subpanels. [250.24(A)(5)].
6. Bonding jumpers on the supply side of the service (service lateral raceways) must not be smaller than specified in table 250.66. [250.104(C)]
7. Ground rods must be buried below the surface of the earth, not 6? above grade. [250.53(G)].
8. Switches are required to be grounded, whether a metal faceplate is installed or not. Yeah, I know its been required for 6 years now, but I still see this all of the time

. Remember: Grounding one switch in a multigang box does not remove the requirement of grounding each switch. [404.9(B)].
9. 120/240-volt conductors must be separated from class 2 or remote/signaling circuits. Check the fireplace switch location and the doorbell chime location (also, the doorbell transformer). Permanently installed barriers can be used to separate the two voltage system where installed in the same box. Note: This does not apply to the cable, such as NM, it applies only to the conductors (inside the NM cable). [725.55].
10. White conductors in cable assemblies (such as NM cable) are not allowed to be used as ungrounded (hot) conductors, unless re-identified as other than white or green. This is very common for three way switch applications. Conductors installed in raceways (such as the liquid tight for an A/C) must be the correct color, and re-identifying a white conductor is not permitted. [200.7(C)].