The circle shows the third prong or equipment grounding slot in a three-prong receptacle.

What is the equipment ground?

The equipment ground in residential wiring is often thought of as the “third prong” in an electrical receptacle and the third, bare conductor in an electrical circuit. Residential wiring systems will function properly without an equipment ground but these conductors make our electrical systems safer by providing a low resistance path for fault current to return to the electric panel and trip the breaker to disable a dangerous fault condition. Houses built prior to the adoption of the 1962 electrical code rarely had equipment grounding conductors. Most of these houses were “two-prong,” or “two-wire,” system.

What is an open ground?

An open ground is when you have a three-prong receptacle that is not connected to an equipment grounding conductor. This is unsafe because an appliance that is designed to use an equipment ground to discharge an unsafe fault condition will not have a conductor to discharge that fault. Open grounds are common in houses built prior to the adoption of the 1962 electrical code. When old two-prong receptacles are replaced with modern three-prong receptacles and a grounding conductor is not added, you create an open ground. You can also find open grounds in post-1962 houses where the equipment grounding conductor has been disabled for one reason or another.

Is an open ground unsafe?

A residential electrical system is less safe when there is no equipment ground and this condition is exacerbated when you have an open ground. To understand why, visualize plugging in an appliance that has a metal jacket that could be energized – maybe an older power tool or vacuum. If that jacket becomes energized the design of the appliance is to discharge that fault onto the equipment grounding conductor…. but there is no conductor present to discharge the fault. Your chances of electrocution have gone up. This is bad, but it can be worse. If this same circuit also has reversed polarity, where the hot and the neutral are backward, also a common defect, you could now energize the appliance jacket just by plugging it in. You would not even need to switch the appliance on to get electrocuted. This is a common electrical safety phenomenon: one thing wrong is a little unsafe but multiple defects can quickly escalate into a serious safety hazard. This exemplifies why it is so important to take even little wiring problem seriously.

How can I safely repair an open ground?

Here are some options for correcting this relatively common problem.

  • The first step is to determine if there is an equipment grounding conductor present on the circuit. Post-1962 houses are likely to have a three wire system and the conductor has simply become disabled. In this case, you need to diagnose this circuit and find where the circuit has become disconnected.
  • In houses wired with a 2-wire system, typically pre-1962, you have many different options for repair. I will review 4 of the most common repairs.
    • The most obvious and most expensive repair is to re-wire or run new three-wire cables in the house. This is ideal and recommended during renovation work, but is expensive and can necessitate opening up wall or ceiling finishes. This may not be the best option unless you are renovating.
    • You can run an equipment ground to the receptacle and connect that equipment ground to any part of the grounding electrode system. This may or may not be easier. You are no longer allowed to bond to metal piping. This is because the rise of plastic water supply pipes makes it too easy to inadvertently disable the ground connection.
    • Another satisfactory repair, that is often the most cost-effective is to protect the circuit with GFCI protection. This can be done with GFCI receptacles or with GFCI protected circuit breakers at the electric panel. GFCI protection is designed to trip a circuit when it detects fault conditions. These are effective and will function properly on a two-wire system. This is an excellent and relatively inexpensive repair compared to re-wiring. Open grounded receptacles that are GFCI protected should be appropriately labeled and this repair will not protect your equipment in case of a surge, so it is not the best repair for media areas and offices.
    • Believe it or not, replacing that receptacle with an older two prong receptacle is considered an adequate repair. This would leave you with a two-prong or ungrounded plug. Not ideal, but better than an open ground.

I hope this brief article gives some insights into what an open ground is, how it can be corrected and why it is so important to repair.