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I have a 50 year old home. I am doing some remodeling and found that I have 2 separate circuits sharing the same neutral. I hadn't seen this before and I am worried about it. Is this in itself a problem?
Also, the neutral is hot where I am remodeling but not at the breaker box. Do I have a short circuit somewhere. I a thinking of pulling new romex and get rid of this tangle but that is a lot of work. Any advice is appreciated.
2 hot may share a neutral provided the 2 hot are not in the same phase (208 v... ).. you may get a HOT neutral if that neutral is share with a fluorescent lite
Thanks. I appreciate the answer. I do have a flourencent on the cicuit. Why would a flourencent cause the neutral to be hot?
Sharing neutrals is a dangerous shortcut that was all too common in the past. The neutral carries the same amps as the hot. Circuit breakers and fuses limit the current the hot can carry, but nothing protects the neutral from carrying twice its rated load. Ripping the whole thing out and redoing would be the best thing, but I would at least take care of the neutral problem. Think of all the news articles that mention the fire started in the wiring.
Labman,
Thanks for the advice. I will replace the wiring.
... are the cause of the increased neutral currents particularly when the fluorescent lamps are ganged together and share a common neutral. See this link for more info: http://www.electrical-contractor.net.../Harmonics.htm. Although the article may not be as thorough as you like, it is a starter.Quote:
Originally Posted by jasv
You can share a neutral with 2 loads if the loads are connected to different poles. When connected this way the neutral will carry the difference between the loads.. not the sum of the loads. If you were to get the 2 breakers on the same pole however then the neutral would indeed carry the sum of both loads. Just measure the voltage between the 2 hot wires.. if it's 240ish then you're on different poles... if it's zeroish then you're on the same pole and that's not good. Just my 1/2 cents worth.
Since my earlier post, I have tempered my aversion to shared neutrals. I hope that within 3 days of when I quit learning and reject any new ideas, they have the decency to bury me. I still wouldn't wire up a house that way. It is true, that if on opposite poles, the neutral will not be overloaded. On the other hand, if I flip the breaker to work on a circuit, I want both the hot and neutral to be dead, not me if I disconnect the neutral.
The guy that taught me much of what I know about wiring hated and despised shared neutrals. I think he was thinking of examples such as the classroom wing of my church where as many as 4 circuits share one little #12 neutral.
On the other hand, if I ran 2 circuits in my house, I would have a total of 6 wires. However, if you check my incoming service, you will count 3 wires, the 2 hot phases, and only one grounded neutral.
Not suggesting Jasv shares neutrals, just letting him know it's possible if done correctly. Shared neutrals are fairly common in commercial work because everything is labeled, there are prints and pretty much only electricians work on the electric. Houses however... yikes.
Doing as Labman suggested, replacing the wiring with new, will probably solve the underlying issue that has not been addressed.
The neutral is hot probably because of reversed polarity, simply put, someone connected the white wire somewhere to a hot wire between where you have the line voltage and back to another outlet in the circuit, but then is wired correctly between that device and the panel.
Being 1950 wiring, the cable you have is usually difficult to tell which is black and which is white. Someone did not pay close attention to the color code or just was not knowledgeable enough to be sure polarity was correct.
A properly wired circuit, no matter what load is served, will not cause a neutral to be hot with line voltage, esp. in only part of the circuit. If this was the case, the entire system's neutral would be hot, right out to the utility, and this will not happen, again, and I emphisize, if wired properly.
A true neutral, wired correctly, is intentionally grounded at several locations, to insure the neutral conductor of a system is at zero potential.
Another situation that may have caused you to believe the neutral was hot would be if you opened the neutral circuit by taking a splice apart. If there was a load still in the circuit downstream, and you either touch both whites wires, or, hopefully tested across these two wires, you will find line voltage. Labman refers to this by shutting off one circuit and leaving one on, and breaking the neutral, for which is still in operation due to the live circuit he did not shut off.
Replacing the cable, and paying close attention to the color code, will invariably make this problem disappear. Sharing neutrals was and is popular in house wiring, and still is done in commercial, esp. for fluorescent lighting. Circuits designed with the same amount of fixtures on each circuit, either 120/240 single phase or 120/208 or 277/480 three phase will have zero amps measured at the panel.
One three phase 277/480 volt neutral can be the return for 32 fixtures at 1/2 amp each, totalling 16 amps on each circuit, totalling 92 fixtures, and you will find zero amps on the neutral. And there will not be line voltage on this neutral wire. If there is, there exists a larger problem than the shared neutral.
However, I will not allow shared neutrals utilized on any branch circuits for power on my jobs, due to the amount of critical equipment found on circuits now, and one break in the neutral can cause a tremendous amount of damage, due to the sensitivity of the equipment.
I realize you have received a lot of information for your question. Since you will be replacing the wiring, take note of exactly what you find, be sure to have the neutral wired through the entire circuit as white, and get back to us with the results.
To be honest the cost of lets say 14-3 and 14-4 is not all that much different. And the cost of a single run of 14-4 will always be cheaper than 2 of 14-2. I am a big fan of 14-4 and use it on almost every residential rough in. Once you make the jump to commercial and light industrial ( I have honestly little real Industrial experience) pulling shared neutral through conduit becomes more and more attractive. It reduces the number of conductors saving on wire and reduces the pipe size needed to pull them. While the comments on equipment sensitivity are ABSOLUTELY valid... one must consider that the cost saving in both material and labor hours make using them to secure a bid a requirement at times. I always make certain to note on the indexes and the files electrical plans that the circuits share a neutral. And whenever possible I am certain to allot for a separate lug for all neutrals. Nothing worse than having 2 neutrals under one lug and having to move one. I see it on almost every call that requires installation of tandam breakers or relocation to fit 2 poles.
Thanks for the input all. This helped me understand a circuit in my house that I came across.
I am in a similar boat... early 1940's house with about 1/4 older wiring. The runs that I have done were replaced with 12-2, with an arch fault breaker. That was all fine and dandy until I came across the 2 circuits for the second floor in which the neutral is shared. I can not replace the run with new without significant cost due to limited access and a flat roof, so there is no attic. So the next solution until I'm in a position to find a way to replace the run was just to put the arc fault breakers in. Not an end all solution... but a bit safer then where I am now. Yes?
My question, is an arc fault breaker similar to a GFCI breaker in this circumstance? Pretty much impossible to do with a shared neutral?
Yes using a shared neutral with an Arc Fault device is not possible.
I have a 240 volt circuit (12-3 with ground) that currently serves wall heaters (1800 watt) in two bathrooms. The wiring is generally inaccessible except where it comes into the bathrooms. I'm planning to remodel one bath and will no longer need an electric heater. Can I convert the heater in the other bath to 120 volt use (say using the red wire as load) and use the black wire for a separate circuit in the other bath (using the black wire as load)? If I can do this, could I use a GFI receptacle on the black wire circuit?
You can make 2 circuits that way. I might even do it that way. However, I am afraid if you look at some of the other threads here, you will find out GFCI won't work with shared neutrals.
Thought about this some more. I remember ratting out some non working outlets a month ago, 2 circuits on one neutral, regular inside and GFCI outside. I cleaned up some connections and replaced a 20 year old GFCI, and when I walked away, everything was working.Quote:
Originally Posted by labman
It was brought to my attention that a statement I made regarding the grounding of a neutral may be confusing.
I said:
"A true neutral, wired correctly, is intentionally grounded at several locations, to insure the neutral conductor of a system is at zero potential."
What I should have stated is is that the neutral is intentionally grounded at several locations BEFORE coming into a building, along with one ground point in the building.
Once in a building panel, that is the last ground point allowed, and is referred to as " Single Point Grounding". All wiring in a building is to be connected so that all neutrals and equipment grounds are brought back to the main neutral, and that no other "grounds" beyond the main panel are allowed.
Explaining why may be even more confusing so I will leave it at that. If a more detailed answer is need for a specific reason, ask and we can go from there.
UGGG,
I just did all my wiring (owner/builder), mostly with lighting on one side, recept. On another, and both sharing a neutral. Now I read tkruseell saying basically, you can't use ARC or GFCI with shared neutral. Is there any way to use both those protections, with shared neutrals? As my 6 year old say, "Please say yes!" Thanks.
I have submitted a correction regarding shared neutral and GFI and AFI breakers.
Please refer to the following:
https://www.askmehelpdesk.com/showthread.php?t=19007
215.4 Feeders with Common Neutral.
(A) Feeders with Common Neutral. Two or three sets of 3-wire feeders or two sets of 4-wire or 5-wire feeders shall be permitted to utilize a common neutral.
(B) In Metal Raceway or Enclosure. Where installed in a metal raceway or other metal enclosure, all conductors of all feeders using a common neutral shall be enclosed within the same raceway or other enclosure as required in 300.20.
When in doubt check codes...
In a commercial wiring system when using metal conduit it is common practice to use a shared neutral. In a properly wired system the voltage is carried over the hot to the "load" the load converts electrical energy into mechanical, heat, whatever but the energy is spent and the neutral or common simply acts as a second leg of the circuit providing a ground. As defined by our local electric company a neutral or common is simply a ground that has less than 0.1 ohm of impedance. Now we all know grounds do not have any line voltage to them... there is also a secondary machine ground run in all three wire circuits and the conduit serves as a fail safe ground to boot.
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