Hot and Ground Suddenly Reversed
One fine day, you’re just sitting down reading about your next DIY project when the light suddenly goes out! You check the breaker in the electric panel but it’s not tripped.
You then dig out the outlet tester to check out the outlet and any light that glows on the tester indicates that the outlet has power, but according to your tester, the outlet is faulty by a “Hot and Ground Reverse” situation.
To make matters more complicated, however, a little while later, you notice that the light is back on and everything seems fine again. Don’t be fooled, though, as the problem is still present, still doing its damage to the circuit, and probably needs fixing.
At the very least, you need to inspect that circuit for reliability, but first find out the implications of a “Hot Ground Reverse.”
Safety Note: Fixing this problem might be a job for a professional. Unless you have advanced experience with electrical systems, it's safer to rely on a pro.
Step 1 - Understanding the Outlet Tester
An outlet tester is a very basic instrument that simply uses the voltages of every wire in a circuit in relation to the ground but also to each other to light up indicator lights in certain combinations that let you know how your circuit is wired, just as long as the circuit wasn’t wired into a Bootleg Ground to intentionally fool the tester.
In a properly wired outlet, the 120-volts between the Hot and the GND, and also between the Neutral and the Hot, but without any voltage measured between the Neutral and the GND normally indicate a correctly wired outlet (Figure 2).
Step 2 - Finding Out What Hot and Ground Reverse Implies
Your outlet tester simply reads the voltages at specific outlets within the circuit while it is powered and then provides you with a diagnostic from the readings.
The fact that a Hot and Ground Reverse fault was there and then suddenly disappeared without any apparent reason does not make it any less serious but just makes you lucky to have noticed it when you did so that you can fix the faulty connection.
Most of the time, however, the Hot and Ground Reverse situation will present itself as a compound problem.
2.1 - Check Local Outlets
A Hot and GND reverse situation will become a possibility as—for whatever reason—the Neutral side of a circuit becomes disconnected at an outlet or upstream from the outlet getting tested.
Without any load plugged into any of the outlets downstream from the open wire, the tester would simply read an “Open Neutral” fault.
2.2 - Open Neutrals
The possibility becomes reality, however, when a load that is turned on happens to be plugged into any one of the outlets downstream from the broken or loose (disconnected) Neutral, the load such as the light bulb in Figure 3, will interconnect the Hot and the Neutral slots by letting the current travel from the outlet’s Hot slot up into the lamp and back to the Neutral slot on the outlet causing them both to have a 120-volts potential difference with the ground.
The open Neutral line upstream, however, will prevent the current from returning to the panel to complete the full circuit, keeping the lamp from lighting up. Unplug the load from that circuit and the tester would then show “Open Neutral.”
The Hot and GND Reverse fault, therefore would show at any outlet downstream from the break and thus require some tracking along the affected line to pinpoint the origin.
2.3 - Bootleg Ground
There is a situation called a “Bootleg Ground”, very unlikely to be the problem in this particular case, but worth mentioning anyway. It is encountered mostly in older houses built before the mid-sixties that were wired with 2-wire cabling encasing only a live wire and a neutral without a ground wire.
That made it impossible to properly hook up the ground lug of a 3-prong outlet and resulted in the tester’s indicator lights showing an “open ground.”
Cheating by connecting the GND terminal with the Neutral wire, however, caused the tester to measure 120-volts across GND and Hot as well as across Neutral and Hot while no voltage appeared across GND and Neutral, thus activating the “proper wiring” indicator lights.
That was a risky and dangerous code violation, however, that defeated the purpose of grounding electrical circuits.
Although not likely to be intermittent and “suddenly disappear”, the Bootleg Ground further miswired by reversing the Hot and the Neutral wires as shown in Figure 4, will also result in a Hot and Ground Reversed diagnosis from the tester as it measures 120-volts across the longer Neutral slot and the ground on the outlet.
Such a situation is known as a “reversed-polarity Bootleg Ground”, and presents a much more lethal hazard as it puts 120-volts on all chassis and other grounded connections within that circuit.
Step 3 - Troubleshooting the circuit
Having eliminated the possibility of a Bootleg Gnd, the other probable cause remaining would be an intermittent open Neutral and could result from any of the following problems within an outlet, a fixture, or a switch, none of which will be obvious to see or find.
- Loose Neutral backstab (push-in) connection in an outlet.
- Loose Neutral terminal screw connection.
- Loose Neutral wire inside a wire nut connection with white wires.
- Loose busbar terminal screw at the electrical panel.
3.1 - Identify the Outlets on the Circuit
In your case, as soon as the problem has disappeared, you’ll need to identify every outlet and every fixture and outlet connected to the circuit. When in doubt, get someone to switch the circuit’s dedicated breaker off and on to confirm each one.
3.2 - Switch Off the Breaker
Once you’ve completed that, make sure to turn the dedicated breaker off before tampering with the circuit and pulling out the wiring.
3.3 - Open the Outlet
You can then return to the outlet or the fixture that initially appeared faulty. Knowing that the problem at this location could be generated upstream, you can proceed with opening up that electrical box and pulling out the wiring from inside it.
3.4 - Inspect the Connections
Check for burnt or melted housings, terminals, and wire jackets as an intermittent connection that keeps going on and off will generate excessive heat. Using the proper screwdriver, check for a loose terminal screw on the socket or on the outlet.
Using needle-nose pliers, check the wires plugged into the backstabs to make sure that they’re secured and tight, then check the Neutral wires from each of the wire nut connectors. If all is good, you can then tug from several spots along each Neutral wire right from the cable connector, to make sure none of the copper wires are damaged within their jacket.
Note—A backstab connector is a connector that instead of securing a wire with a terminal screw uses a tension-loaded blade inside an opening at the back of the outlet and into which a wire is inserted and pushed in through the retaining edge of the blade which in theory grabs it and secures a positive connection to that terminal.
Such connectors, however, are known to eventually loosen up their tension especially when the outlet or switch is handled periodically.
3.5 - Repeat at Other Outlets
If all checks out OK, put it back together and proceed to the next terminal box upstream. Repeat every step listed in 3.4, until you come across the loose connection.
Note—Whenever you come across a terminal box with only one cable feeding into it, that box is the end of a branch and can be dismissed as the one at fault.
3.6 - Inspect the Panel
After inspecting every terminal box without finding any loose connection, you’ll have to consider the possibility of a loose Neutral connection on the Neutral busbar inside the main panel.
Set up a battery-operated trouble light, turn off the power to the whole panel by switching off the main breaker at the top of the panel, and remove the cover to expose all of the wirings inside.
3.7 - Identify the Circuit
Locate which cable connector the circuit’s cable goes to inside the panel and follow the white wire (you will probably need needle-nose pliers to move it and follow it around) and find which terminal screw on the busbar is used to secure it in place.
3.8 - Tighten and Secure
Use your slot screwdriver to tighten up the terminal lug screw and secure the wire. You can now replace the cover panel and secure it in place.
3.9 - Power Back Up
Turn the main power breaker back on.
If none of the steps above resulted in finding the cause, you should explore the possibility that a fixture such as a ceiling fan might have been installed using the handiest live cable found in the attic.
Troubleshooting intermittent problems can become extremely frustrating and requires a lot of patience and perseverance, but armed with this info and a receptacle tester, you’re now ready to make your home a safer place.