Mike Dolt Enterprises
Mike Dolt Enterprises
User: Upright Mike, Location: Lakes Region, NH
Asked on: Thursday, March 6, 2025 at 8:42 pm EST
Answered on: Thursday, March 6, 2025 at 9:13 pm EST
Question: Hello all,This week, I was working on a small residential remodel project in a fairly new house built within the last 8 years. While we were there, the homeowner asked us to look at some electrical issues he had been experiencing since the house was built. One of the problems had to do with a bedroom switched outlet. He showed me that every time he plugged a nightstand lamp into the receptacle outlet behind the nightstand, it would trip the breaker. We identified there was nothing wrong with the lamp itself because it worked fine when it was plugged into other receptacle outlets, and everything looked to be in safe and good working order. When another cord-connected piece of equipment was plugged into that receptacle, it would also trip the breaker instantly. This would happen regardless of whether the single pole switch controlling the switch conductor for the outlet was closed or open. I started by removing the devices in the switch box and inspecting the wiring. It was pretty straightforward: the box was being supplied by a 14/2 NM cable, and the black was pigtailed to supply the line side of the two switches in the box. The two other cable assemblies were 14/3; one was for the switched outlets, and the other was for a ceiling fan. The red conductor of the 14/3 assembly that was supplying the receptacle outlets was being used as the switched conductor. I traced out where that cable assembly went first and then proceeded to take that outlet box apart. In that box, there were two 14/3 NM cables, one from the switch box and the other went to the outlet box to the right of this one, there was also two 12/2 NM cables that were spliced together and on separate circuits of a different phase. The issue I found immediately was that instead of the 14-gauge conductors being connected to the receptacle outlet and being separated from the other circuit, the 14/3 that was supplying the outlet box to the right of it, the black conductor and the white neutral conductor were spliced together with the 12/2 conductors not the 14/2 two conductors coming from the switch box they were terminated on the device. The outlet box to the right, which was being supplied by the 14/3, which black and white conductors were spliced together with the 12/2 in the other box, was the last switched receptacle outlet. There were only two in the bedroom, one on each side of the bed. The only other cable assembly in the second box was a 14/2, which was supplying the next receptacle outlet on the wall to the right of that in the same bedroom. I separated the14/3 conductors from the 12/2 conductors in the first outlet box and remade them properly, like a normal switched outlet setup. The tabs were already broken on the hot side of the receptacle outlet; the red switched conductor terminated on the bottom, and the constant power black conductor terminated on the top. After I separated them and kept them on their appropriate circuits 14 to 14 and 12 to 12 everything functioned properly. That same lamp was connected to both sides of the receptacle and worked fine with out any tripping. I try not to cast shade towards other electrical contractors, but the whole electrical system was very poorly wired. We found a lot of bad connections and just sloppy work that had to be corrected. My question for the forum is, can anybody explain the theory of why this happened? Was the reason that caused the circuit breaker to trip when the black and the white of the 14/3 was connected to the 12/2 conductors of another circuit causing a phase to neutral short? Or was it because the current was trying to flow back on the opposing phase when the cord was connected it somehow completing the circuit? I believe this was not a phase-to-phase short because I think both circuit breakers would have tripped. Sorry for the lengthy question, I just wanted to give as much details as I could. I have found similar issues that others have posted on this forum, but my situation was a little different from what was posted. I want to thank everybody who has contributed to this forum. I greatly appreciate all the information that is shared here.
Okay, that's a doozy of a wiring mess! It's good you found it and corrected it. Let's break down why it was likely tripping the breaker.
Here's a likely explanation for the breaker tripping, combining the issues you identified
The core of the problem was the unintended
parallel paths and potential for current sharing that resulted from connecting the 14/3 conductors (black and white) to the 12/2 conductors of another circuit. Parallel Path
By splicing the black and white conductors from the 14/3 cable (controlling the switched outlet) to the 12/2 cable of a different circuit (potentially on a different phase), you created a parallel path for current to flow. Instead of all current flowing through the intended circuit (the one providing power to the switched outlet), some current could take a "shortcut" through the other circuit.
Current Overload
When you plugged something into the switched outlet, current would try to flow through both circuits. The 14-gauge wiring is only rated for 15 amps, while the 12-gauge is rated for 20. The parallel paths likely caused one or both circuits to exceed their rated ampacity, leading to the breaker tripping.
Phase Issue (Possible, but Less Likely Primary Cause)
You mentioned the possibility of circuits being on different phases. This is a trickier scenario to diagnose remotely without detailed measurements.
Why not a Phase-to-Phase Short?
You're right that a direct phase-to-phase short would likely trip both breakers involved instantly and violently. The scenario you described, while dangerous, wasn't a clean phase-to-phase short. It was more of a convoluted current sharing situation.
Here's a simplified way to visualize it
Imagine two water pipes connected at multiple points. If you open a valve on one pipe, water will flow through both pipes to some degree, rather than just the intended one. If too much water tries to flow through either pipe (exceeding its capacity), a safety valve will trip.
In your case, the "water" is electrical current, the "pipes" are the circuits, and the "safety valve" is the circuit breaker.Important Considerations
Overloaded Neutrals
When you create parallel neutral paths, it's easy to overload the neutral conductor. Neutrals are sized to handle the maximum current of the hot wires they serve. By creating unintended parallel neutral paths, you can exceed the neutral's capacity.
Harmonics
Non-linear loads (like many modern electronics) introduce harmonics into the electrical system. These harmonics can exacerbate neutral overloading and other power quality problems.
Arc Fault Circuit Interrupters (AFCIs)
Many jurisdictions now require AFCIs in bedrooms. These devices are designed to detect arcing faults, which can be precursors to fires. It's possible that the original wiring fault, even before fully tripping the breaker, was creating conditions that could have eventually triggered an AFCI.
Good Work Correcting It!
It sounds like you did a thorough job tracing the problem and correcting it. By separating the circuits and ensuring that each conductor was properly connected to its intended circuit, you eliminated the parallel paths and the potential for current overload.
Lessons Learned
This situation highlights the importance of meticulous wiring practices. Never assume that wiring is correct, even in newer homes. Proper troubleshooting is essential to identify and correct electrical problems.
Always De-energize
This should go without saying, but always de-energize circuits before working on them. Using a non-contact voltage tester is a good practice to verify power is off.*
Load calculations: Make sure that the load is properly balanced across the phases and that the neutral conductor is properly sized to handle the load.I hope this explanation helps. It's a complex situation, but understanding the underlying principles is key to effective troubleshooting. Keep up the good work! Flag for review