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I am trying to figure out the circuitry in a room where two different switches can turn a light on or off, and there is a second light controlled by a single switch. Each light is on a different circuit breaker. I disconnected all the wires at the light switches and also at the light fixtures and checked for voltage between all the ends of the wires, with the circuit breakers in all possible positions. In cases where no voltage was measured, I also checked for continuity.

It seems to me that the only way my results make any sense is if, when in the "off" position, each circuit breaker grounds out the attached circuit so that it has continuity with the bare copper wires that are attached to the light switch boxes and also to the light fixtures.

Does this make any sense at all? I always thought that a circuit breaker was a simple "make or break" device that either connects the circuit or interrupts it. Am I wrong? (Actual question: Can a circuit breaker actually ground out the circuit when in the "off" position?)

The house was built in the 60's and most of the outlets don't have the third opening for a grounding prong, if that makes any difference. One of the light switches had a green screw for an earth ground wire but nothing was connected to it. However the metal receptacle box that the switch was installed in did have a bare copper wire attached to it. The other light switch lacked the screw for earth ground entirely but again was installed in a metal receptacle box with a bare copper wire attached to it. Each of the two light fixtures also has a bare copper wire attached to it. There is continuity between all these bare copper wires regardless of the position of the circuit breakers, even with all the wires disconnected from the light switches.

It proves necessary, I can edit the question to include all the results of the tests for voltage and continuity, but I thought I'd start w/ just this info.

UPDATE --thanks for the answers so far. We've discovered that the apparent grounding appears to be simply due to other things plugged into electrical sockets that are on the same circuits as the lights. When checking for continuity or lack thereof between points on two different circuits, one with the breaker on and one with the breaker off, there can be an electrical path from the "hot" circuit through the multimeter through appliances plugged in to the (normally hot side of the) "cold" circuit and on to ground. This can give the illusion that the open circuit breaker is somehow grounding out the "cold" circuit. This can also create the possibility of measuring a 120v voltage drop between a point on the "hot" circuit, and a point that would normally be "hot" on the "cold" circuit.

In this particular case, when one of the breakers was off, points on that circuit were connected to ground through a whole-house vacuum that was plugged into a wall outlet. The measured resistance was actually about 35 ohms, not zero. When that appliance was unplugged, the resistance between the two points being measured on the two different circuits went from 35 ohms up to infinity. When the other breaker was off, the grounding was through a computer power supply-- I don't have that resistance reading handy right now.

It doesn't appear that anything has changed in the wiring from the original configuration, so that does not seem to be the reason that the lights are not turning on now. The original issue was a bad switch which has now been replaced-- as for why the lights are not yet coming on, it's possible but not yet certain that a ballast got damaged at some point during the circuit testing, or a fluorescent bulb or one of the "keystone" mounts got damaged at some point as the bulbs were being removed for circuit testing or re-installed afterwards.

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    "two different switches can turn a light on or off" is called a 3-way switch (US, 2-way ROW). You're saying that each switch is on its own breaker??? Your best bet it to turn off all breakers involved, remove cover plates, then unscrew switches from their mounts, & pull them out of the box without removing any wiring. Get us good, clear, focused pics of the wiring, identifying which switch is which and what it controls.
    – FreeMan
    Commented Feb 1 at 13:32
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    What exactly is your issue? What are you attempting to correct?
    – RMDman
    Commented Feb 1 at 13:33
  • Depending where you are measuring, neutrals are bonded to ground only in the main panel. With lights there is a path between hot and neutral, which would lead to ground. Circuit breakers do not connect to ground. Big sparks/fire will happen if they did.
    – crip659
    Commented Feb 1 at 13:38
  • Re "What exactly is your issue? What are you attempting to correct?" -- I am trying to make sense of my voltage and continuity measurements. So I am trying to understand if the circuit breakers are grounding out the circuit when in "off" position. If circuit breakers don't ever function this way then I am seriously not understanding something about the circuits. The exact issue is that one of the light fixtures only comes on dimly but there may be a problem with the bulbs or the ballasts (they are fluorescent). Commented Feb 1 at 13:39
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    @quietflyer, The bulbs or the ballast is faulty. There is nothing wrong with your breakers.
    – RMDman
    Commented Feb 1 at 13:44

3 Answers 3

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To answer your direct question: "Could a circuit breaker connect to ground when off?"

No. Circuit breakers don't connect the power wire to ground when off.

Most standard circuit breakers don't have any connection to ground or neutral, only between the power wire of the circuit and the power bus in the panel. So they are physically incapable of jumping power to ground.

Note that some fancier breakers (GFCI, AFCI) may have a connection to neutral, because the neutral for the circuit must come to the breaker first so it can be tested. The likelihood of these breakers jumping the power wire to the neutral when off is extremely unlikely.

Your interpretation of results can remove the idea of the power and ground/neutral wires being connected when the breaker is off.

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  • Thanks, but I'm baffled. I may have to post a new question showing all the results of all my measurements and ask if anyone can figure out what is going on. Commented Feb 1 at 13:43
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    A new question with your results would be best. The above is to let you know that you don't have to include the idea that power and ground are getting connected, This may influence your new interpretation and get you closer to the correct understanding of the circuits. Commented Feb 1 at 13:47
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    FWIW some loads still connected to the circuit, like incandescent bulbs or motors, can allow continuity tests through, and make it look like power is connected to ground. Removing all loads as well as turning off the breaker is necessary to trace wires, etc. Commented Feb 1 at 13:50
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In the US at least, circuit breakers are never (OK, I'll bet there is some special industrial situation that's different - we're talking DIY residential here) set to ground anything when turned off. Rather, they break a connection on a hot wire (sometimes two hot wires - a double breaker) when there is an overload or some other problem condition (ground fault, arc fault). They don't turn around and connect that wire to something else - that would be hard to do in an overload situation and not a good idea for a bunch of reasons.

Back to the real problem:

Tracing out wires and figuring out what each one does can get complicated. My hunch is that this is either a skill issue, and that with practice you will get better, or a tool issue - i.e., not using a tester in the proper way to get a definitive result.

However, there are two particular code violations which are, unfortunately, not that unusual and which can cause an expected "hot" wire to show continuity with ground and/or actual neutral:

  • Hot/Neutral Reverse

In this case, the standard black wire is connected to neutral and the standard white wire is connected to hot. Devices can't tell the difference unless they compare hot and/or neutral to ground (0V instead of 120V hot to ground and 120V instead of 0V neutral to ground). This should never happen at the circuit breaker - simply too obvious a mistake. But it is quite common with DIY installations of receptacles (and probably a few careless professionals). Typical is a daisy chain of receptacles where at one location the ongoing cable has black to neutral and white to hot. Nothing appears wrong unless you check against ground. And if the next receptacle is not grounded (common in 1950s and older in the US) then it is even less obvious and doesn't have any effect whatsoever on normal operation. But it is wrong, and it will result in a test at any point after the reversal showing black to ground continuity when the breaker is off.

  • Switched Neutral

This is generally a more deliberate situation, but with switch loops it could simply be DIY installation confusion (the previous installation, not your current work), and it can also piggyback unknowingly on a prior hot/neutral reverse in the circuit. There are safety reasons why switching hot is preferable to switching neutral and that is why code requires it. But again, if neutral is switched instead of hot the lights will still work just fine but a "hot" to ground test will show continuity.

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  • manssehkatz, thanks, and see new info my "answer" -- Commented Feb 5 at 19:52
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If you have two switches controlling single light, they will be A/B switches. In contrast to regular On/Off switches, these connect to either A or B lane. How this works is that one switch has Hot as input, and A/B as outputs. The other switch is wired in reverse, with A/B as input and other side has hot that goes to the bulb. When both switches are in "A" position, the power goes through the A line, into a bulb, and you have light. If One switch is in "A" position and the other in "B" position, they are connected to different lanes and power does not flow. If Both are set to "B", then again the power goes through, the B lane this time, into a bulb and you have light.
It is important to remember that switch is always connecting to either A or B, there is no full off position.

As a caveat - it is possible to add more switches between the two, these are cross switches that have 4 leads, two inputs and two outputs, and swap the outputs around. You might have one of these used as the A/B switch sometimes.

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  • The standard term for the "A/B switch" you refer to is "three-way switch" in North America, or "two-way switch" in Continental practice, for folks at home who might be a bit confused by this answer at first, although it's a good explanation of how conventional travelers work :) Commented Feb 3 at 3:33
  • Thomas, thanks, and see new info my "answer" -- Commented Feb 5 at 19:52

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