The National Electric Code (NEC) is the standard for electrical installation and repair in the US. The code is updated regularly and outlines the current safety requirements when dealing with electrical work. While the code is always changing, some of the more recent changes are outlined below.
A ground fault circuit interrupter (GFCI) is required for all receptacles in wet locations defined in the Code. The NEC also has rules about how many circuits and receptacles should be placed in a given residential dwelling, and how far apart they can be in a given type of room, based upon the typical cord-length of small appliances. This mainly applies to bathrooms, kitchens and outdoor outlets.
In the code for 1962 the NEC required that new 120-volt household receptacle outlets, be both grounded and polarized. The NEC also permits grounding-type receptacles in non-grounded wiring protected by a GFCI. The 1999 Code update required that new 240-volt receptacles be grounded also. These changes in standards often cause problems for people living in older buildings.
The arc-fault circuit interrupter (AFCI) detects arcs from the hot wire to the neutral. These can develop when the insulation between the wires becomes frayed or damaged. Hot to neutral arcs do not trip a GFCI device, but an AFCI device detects those arcs and will shut down a circuit. They are required in new construction on all 15A and 20A 125V circuits to bedrooms, which is where most arc fault fires originate.
In some residential construction, wiring is allowed to be directly installed in the walls without any additional protection or insulation. However, in commercial buildings, wiring must be protected from damage, so it is generally installed inside conduit piping. If a wire is pulled with just enough force to stretch the wire without breaking it, then it becomes a hazard of future failure or electrical fire. Wires must also be protected from sharp metal edges of conduits or holes. The NEC specifications protect wire insulation from being damaged by these sharp edges during installation. In wet locations, a different water tight conduit may need to be used to keep moisture out.
If you are interested in learning more about electrical code and safety standards you can visit the National Fire Protection Agency site’s National Electrical Code® (NEC®), page.