Help tracing multiple paralleled neutrals

[SilverFox]

I have 6 paralleled neutrals from 6 separate breakers located in the main panel. All are 120v circuits. This is in a 7000 sq ft, 3-story residence. I need to find the place or places where these 6 neutrals come together. When I remove each neutral from the main panel bus, I see a short circuit from each neutral to the bus, and I see a short circuit from each neutral to each other neutral. They all seem to be in lighting circuits (mostly ceiling cans).

I have an Amprobe AT-2004 tracer. But with so many wires going to so many circuits, the receiver sees signals all over the place!

When troubleshooting 2 paralleled neutrals, it is easy to trace, or to divide the circuit in half somewhere and trace to the other half ("divide and conquer"). But with 6 interconnected circuits like this, I'm finding myself chasing my tail.

You may wonder how this could have happened, especially since the building was gutted and remodeled just 10 years ago. There were 3 different electricians working on it. I spoke with one of them, who was totally unfamiliar with there being any problems with MBC neutrals, and didn't even believe me that properly wired circuits will read open from neutral to the neutral bus, unless there is another paralleled neutral circuit it is connected to somewhere. I showed him in the main panel how other circuits were okay by removing other neutrals from the neutral bus and showing him with an ohmmeter that they read open to the bus when they are disconnected from it, if they are properly wired. What this tells me is that this guy might have actually joined some or all of the paralleled 6 neutrals together, possibly in several different places, and that I'm likely not seeing a failure or nicked wire etc. And all of the circuits are working - no breakers blow and all lights and switches work. And yes, there are many 3-way and 4-way switches throughout the house.

Any ideas on how to trace? Any way to get to the place or places these neutrals come together?

 

[Smart $]

Other than divide and conquer, one suggestion sticks out in my mind...

Trace the hots.

 

[GoldDigger]

Other than divide and conquer, one suggestion sticks out in my mind...

Trace the hots.

Have you also confirmed that when you remove all six there is no continuity from the merged neutrals to ground?
Since it is six circuits, (all going to same renovated areas?), it could be that all of them were individually connected to something else rather than that they were brought together to one place and tied together.
Since you were doing this checking with the main breaker open, is there any chance that what you were seeing was actually a load resistance (like primary of LV lighting transformer) going back to neutral through the hot wires and other loads? Turning off all six breakers (or even all branch breakers in the panel) should rule that out quickly enough.

If the problem is entirely an MWBC type sharing of the neutrals between pairs of circuits, there would have to be a lot of them to bring all six together. Either a consistent deliberate miswiring or an improbable number of mistakes. More likely to have happened at a junction where all six of them were still traveling together. Definitely follow the hots. Find out where all six go as they leave the panel. If nothing else, they will be easier to isolate with your tracker.

 

[gar]

130525-2217 EDT

Get a long extension cord that will extend from the main panel to anywhere in the home. Use one of the wires as a long test lead. I would probably use the EGC of the cord for this purpose. If there is receptacle close to the main panel just plug the cord in. This gives you a reference voltage point at the main panel ground bus.

Use something like a Fluke 27 as a voltmeter in automatic volts AC range.

Use a small portable 1500 W heater as a test load. Try to use existing receptacles as test points if possible. But from your description you may need to make an adapter to screw in light sockets if you want to apply the test load there.

The heater will produce about a 10 A load. The resistance of #14 copper is about 0.025 ohms per 10 ft, and #12 about 0.016 ohms. 10 A at 0.025 ohms is about 0.25 V per 10 ft, and for #12 about 0.16 V per 10 ft.

At the main panel open all breakers and their neutrals except one circuit. Try to put the heater load at the farthest point of the powered circuit. At the main panel measure the voltage between each opened neutral and the ground bus. If all the voltages are the same, then there is likely a common connection point.

Next measure the main panel ground point to the neutral where the heater load is located. I am assuming you will have a duplex receptacle for the test load point. To eliminate the voltage drop of the heater plug into the receptacle make the neutral test point the unused neutral slot. If this voltage drop is the same as you measured at the main panel, then the common connection point is beyond the receptacle or near the receptacle. If the main panel voltage was substantially less than the voltage at the test load point, then the common is at an intermediate point. The voltage ratio will tell you about where.

Also do this voltage measurement at the receptacle EGC pin. There might be an incorrect connection to EGC somewhere.

Things can be more complicated, but this might start you with a troubleshooting procedure.

Note: I can use this test procedure to determine how a circuit connects from one outlet to another.

.

 

[cadpoint]

I don't know of your equipment but a telephone tracer will work, also called a fox and hound.

I'd disconnect all circuits first at panel and ring out the circuits. One would have to follow each circuit till initial dead ends and complete the ringing out the circuit. Test any and all circuits for power before any test equipment usage!

What you could do look for the extended connections on either/both sides of the circuit; the hot circuit when you find the shared neutral connection from that persumed end of the circuit and continue to complete the ringing out, respectively. Remember the extra wires can be travelers.

If any of the previously installers were smart all your closest 3 way's would be supplied power at the closet point to the main panel.

Remember that multiple joints could well be in any of the lights.

 

[mbrooke]

Start with the switch boxes most likely the culprit will be there. Looks like someone was carless when splicing the lines up in the switch box. Find where the hots end and what they serve. When one of them shits to another hot, its time to break up the neutral. Switch on one breaker at a time and see what lights up. All the cans that do...well youve got your loads for that breaker. Mark them with tape, do the same for the other circuits: mark each of them with a different color. I am assuming no hots are crossed together. If your worried about crossed hots turn everything on and test between them and the others at the panel. You might also need to do the same with your grounds to neutrals just to see if a ground is in contact with the neutrals. Once you have an idea what is what its time to start going box by box, possibly from cieling fan to ceiling fan.


BTW, tell your electrician to go back to school, obviously he doesnt understand basic electrical theroy/science. I would double check his work just in case something eles is not right.