I have a 50 year old home. I am doing some remodeling and found that I have 2 seperate 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.

caibuadday

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 flourescent lite

jasv

Thanks. I appreciate the answer. I do have a flourencent on the cicuit. Why would a flourencent cause the neutral to be hot?

labman

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.

jasv

Labman,
Thanks for the advice. I will replace the wiring.

Flickit

...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.

eg007

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.

labman

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.

eg007

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.

tkrussell

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 flourescent 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 thru the entire circuit as white, and get back to us with the results.