What colour are the phase neutral and earth cores flexible cords?

Connecting the neutral to the equipment case provides some protection against faults/shorts, but may produce a dangerous voltage on the case if the neutral connection is broken. Combined neutral and ground conductors are commonly used in electricity supply companies' wiring and occasionally for fixed wiring in buildings and for some specialist applications where there is little alternative, such as railways and trams. Since normal circuit currents in the neutral conductor can lead to objectionable or dangerous differences between local earth potential and the neutral, and to protect against neutral breakages, special precautions such as frequent rodding down to earth (multiple ground rod connections), use of cables where the combined neutral and earth completely surrounds the phase conductor(s), and thicker than normal equipotential bonding must be considered to ensure the system is safe.

In North America, the cases of some ranges, cook tops, ovens, clothes dryers and other specifically listed appliances were grounded through their neutral wires as a measure to conserve copper from copper cables during the Second World War. This practice was removed from the NEC in the 1996 edition, but existing installations (called "old work") may still allow the cases of such listed appliances to be connected to the neutral conductor for grounding. This practice arose from the three wire system used to supply both 120 volt and 240 volt loads.

Because these listed appliances often have components that use either 120, or both 120 and 240 volts, there is often some current on the neutral wire. This differs from the protective grounding wire, which only carries current under fault conditions. Using the neutral conductor for grounding the equipment enclosure was considered safe since the devices were permanently wired to the supply and so the neutral was unlikely to be broken without also breaking both supply conductors.

Also, the unbalanced current due to lamps and small motors in the appliances was small compared to the rating of the conductors and therefore unlikely to cause a large voltage drop in the neutral conductor. In North American practice, small portable equipment connected by a cord set is permitted to have only two conductors in the attachment plug under certain conditions. A polarized plug is used to maintain the identity of the neutral conductor into the appliance but it is never used as a chassis/case ground.

The small cords to lamps, etc., often have one or more molded ridges or embedded strings to identify the neutral conductor, or may be identified by colour. Portable appliances never rely on using the neutral conductor for case grounding, and often feature "double-insulated" construction. In places where the design of the plug and socket cannot ensure that a system neutral conductor is connected to particular terminals of the device, portable appliances must be designed on the assumption that either pole of each circuit may reach full voltage with respect to ground.

This connection is made using "unpolarized" plugs. In North American practice, small or large technical equipment connected by a cord set must have three wires, if supplied exclusively by 240 volts, or must have four wires, if supplied by 120/240 volts.