3 – Prong Outlets
Three-prong outlets, also known as grounding receptacles, are necessary for many 120 volt appliances like radios, televisions, computers, microwaves, coffee pots etc. Modern homes are wired with these conveniently located every 12 feet or so along each wall. Older homes (pre-1960) were wired with two-prong electrical receptacles, sometimes just one or two per room. Converting electrical outlets to three-prong type is a job with several technical aspects best left to licensed electrical contractors.
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Grounding appliances by means of the third prong is only assured when there is a good ground connection in the junction box behind the outlet and also a good connection at all the other junction boxes in the circuit. Your new three-prong device is providing a ground connection which is intended to complete a circuit back to the panel to safely trip the breaker in case of a short-circuit in the outlet or the appliance connected to it. Average residential circuits have 72 connections which must be in good condition for all functions to be optimal. Make sure the whole circuit (all the outlets and switches and lights attached to the same breaker) are checked for good connections and any plug or switch which isn’t in new/perfect condition should be replaced at this time.
Not all circuits have a ground conductor.Some homes constructed before 1960 were wired with a type of old romex with dark colored cloth wrapping, some of which did not include a ground conductor. This type of wiring requires an additional ground wire be fished to each outlet to provide the necessary grounding for modern appliances. These cables also have fragile insulation which can cause short-circuits and/or wall fires. Do not touch them. You should seek a licensed professional if you think you may have these wires in your home. Most will offer a no cost, no obligation evaluation and proposal.
Some cables have a metal covering which serves as the ground conductor for the circuit.This cable, called B.X., is still used in commercial construction today. Modern BX has excellent grounding and insulation properties and is extremely tough and resilient, making it ideal for extreme environments like restaurants, stores, warehouses, and light industrial. Older BX (pre-1960) had a type of insulation on the wires which doesn’t hold up to heat and age very well, especially when continuous usage of the electrical circuit continued for decades… or when there is a surface mount light fixture which is used frequently attached to them. The light adds heat to the junction box and causes oxidation of the insulation and conductors. These wires become extremely fragile and should not be touched except when necessary and only by qualified professionals.
Don’t try to convert a two-prong using the grey plastic plug-in converter. These devices create an additional set of connections which attach onto the loose connections of the old plug and do not solve the primary problems. Your ground connection at the plug is only one small part of the equation, and even that part is poorly addressed by these devices.