If your home has an older 2 wire electrical system, it most likely is not grounded properly. It also may not be capable of delivering the power loads needed by today’s device standards. This 2-wire system was often used in knob-and-tube (K&T) wiring which was commonly used between 1880 – 1930’s. Knob-and-tube wiring was insulated with cotton cloth (loom), and soft rubber. Older cloth wiring is easily damaged by renovations and rodents. It would be a wise investment to upgrade, and re-wire your whole house if your system is older than 50-60 years. The cost to re-wire your home may run between 5%-15% of your home’s value. If that is not an option the 2014 National Electric Code (NEC) allows for alternate acceptable upgrades for 2-wire systems.
1) The NEC code allows you to replace existing two-prong receptacles with new 2-prong receptacles. You will not be grounding anything with this option, but just upgrading older (yellow, brittle) receptacles with new (whiter) ungrounded receptacles.
2) The NEC allows you to replace the two-prong receptacle with a 3-prong GFCI protected receptacle, but it must be labeled “No Equipment Ground”. You also cannot ground any receptacles downstream of this installation. There are specific wiring steps involved to switching to a GFCI when the box is not grounded. You must identify the load wire, and line wire and connect this according to the markings on the GFCI receptacle.
3) You can replace the two-prong receptacles with a three-prong receptacle- and add a GFCI protected circuit breaker to the panel. The receptacle must be labeled “GFCI protected, and No Equipment Ground”
Note: You may need to buy the smaller GFCI receptacles to fit the smaller pre-1950 outlet boxes.
Grounding Options :
(These are Not necessarily NEC approved- check with your local Jurisdiction for more details)
There are 3-prong self-grounding receptacles available which can be used if your outlet box is metal, and the box is connected to a grounding system that continues to your panel. There is also an option of to add a ground (jumper bond) from the new 3-pronged receptacle to a metal outlet box – only if the metal outlet box itself is connected to a grounding system that continues to your panel. A good YouTube video from VideoJoeKnows “How to ground an old style electrical box.” (Part 1 and Part 2.) will show you how to add a ground.
Another helpful article I found from This Old House Online “Replacing Two-Prong Receptacles” will show you how to test to see if your box is grounded. (Test to see if your box is grounded by inserting one end of an electrical tester into your hot (short) slot, and touch the other end to the outlet box cover screw. If the circuit tester lights up, then your box is grounded.)
Note: I always recommend getting a certified electrician for all electrical work. Always get a permit for electrical remodeling, wiring, and upgrades to help maintain safe electrical standards for your family. Obtaining a permit also can add value if you choose to sell your home, or loose value if done improperly.
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