You’ll be amazed to know that the US houses built before the 1960s had metal boxes with just two prongs. The Romex had just one hot and neutral wire, no ground wire. And then, somewhere in the 60s, NEC changed, and metal outlet box grounding became mandatory. A ground wire was added.
Now, directly addressing the question of whether a metal outlet box is grounded or not, the easiest answer is that it is ONLY IF it is connected to the ground through a ground wire or a pipe. A metal box doesn’t get an electrical grounding (earthing) just by touching the ground. To act as a ground, it must have a metallic continuity back to the main electrical panel, which can be achieved via copper wires or metallic pipe connections.
In this blog post, we will learn the different ways of knowing if the metal box is grounded and what you can do if it is not. We’ll also see how you can convert non-grounded outlet boxes to grounded ones. Now there are some right ways to do it, and there are also some non-code-compliant strategies to achieve it, which we will dope out in this article.
Where Can You Locate The Metal Box, And What Is Its Role?
The metal box is right behind the wall outlets and keeps the wires and outlet intact. It connects them to the breaker box via a ground wire.
Testing of the circuit breakers is usually complete when you’re given a walkthrough of the new house. But how can you really know if the metal outlet box is grounded?
(You can usually know if the metal box is grounded with an ohm meter by checking for the continuity from neutral to the box. Apart from this, you can use a test light or a voltmeter to see if you are getting full voltage between the box and the hot wire.)
Top 5 Ways to Check If the Metal Box Is Grounded
1. Check with A Non-Contact Voltage Tester
With a tester, you can easily see if there’s a current running through the wire. If there’s no current passing and your ground test is negative, it’s easy to conclude that your box is not grounded.
You will need to install a ground wire for this box before doing any electrical work inside it.
2. Check with Your Hands
Of course, a bit risky, but what do you do if you don’t have a tester? With safety and precautions, you can also use your hands to check the current in the wires.
First, turn off all the power in the house and remove one wire from the metal box at a time. No active ground is attached if you don’t feel current in any wire.
3. Add a Ground Wire and a Rod
This is a foolproof way to know if the metal junction box is grounded. If you see one already there in an adjacent box, connect them.
If there’s not, install a new cable and connect it with a ground rod, and stake it into the earth outside.
4. Check the Breaker Box
The grounding problems may often appear in it instead of the individual wires inside the metal boxes. If you see the ground wire detached, it’s got to be attached with a screw on the breaker box.
In case there’s a subpanel instead of a breaker box, check it the same way. However, they’re usually connected to the ground rods.
5. Look for the Green Grounding Screw on Your Junction Box
If you see one that’s loose or is not screwed at all, it’s indicative of ground wire not being attached to the screw.
To get proper grounding, the electrician would unscrew the wire from where it is connected and attach it to the metal threaded rod of the green grounding screw. This is the most reliable and convenient way of grounding a metal wall box.
What Can You Do To Convert A “Non-Grounded” Electrical Outlet To “Grounded”?
Although you don’t need to get your outlets grounded if you’re living in one of those older houses with no grounded panels, it’s recommended for safety.
There is just one code-compliant way to achieve this: installing a new grounded panel and rewiring the outlets with cables that include a ground wire. Undoubtedly, this is too much work. That’s why NEC has allowed a workaround. You can get the first outlet replaced in each circuit with a ground fault-interrupting outlet. Label every three-prong outlet properly.
Some Non-Code-Compliant Common Strategies
Of course, some unsafe alternatives exist for converting ungrounded outlets to grounded outlets. Knowing these and learning why they’re not code-compliant is also important.
- Using a jumper cable to connect the ground and neutral terminal. It will power up anything you plug into the outlet- even when it’s turned off.
- Running the ground wire to a ground piece of metal or a nearby water pipe.
- Running a detached ground wire back to the grounded panel and attaching it with the ground bus may seem like a good alternative, but it would leave the ground wire open and exposed to damage.
The non-compliant solutions mentioned above may sound feasible, but they’re riskier than leaving the 2-prong outlet as is. It’s because the 3-prong outlet gives an impression of a proper grounding when it’s not the case.
A Word of Precaution
Ensure you’re not opening the metal box without shutting down the power.
Remember that the sharp edges in the metal box can disrupt the cord’s insulation. Hence, check it very carefully before you start working on it.
Final Thoughts
If you’re unsure if your metal outlet box is grounded and you don’t want to go for too much hassle, you can opt for a simple test, such as the buzzing test. Hold an electrical device near the suspected ground wire and touch it with your hand. If the grounding wire buzzes, it’s running current through it.
I hope this post added some value, and now you know how you can identify if the metal outlet box is grounded or not.