If a circuit is fed by a double-pole breaker and has two hot wires, one red and the other black, that would in fact be the normal assumption by someone who understands residential wiring systems: that it's an Edison circuit, and the potential between them is 240V. At a minimum, even to the uninformed it should be a signal to check a little further to find out what's going on before proceeding.
Allowing the two hots to touch is asking for trouble, regardless of the type of circuit. Good practice, when opening up live circuits for testing, is to make sure that *nothing* is touching anything else.
So who's suggesting deviating from the norm? This *is* a common situation. It's "unexpected" only to those who are unfamiliar with Edison circuits.
I agree that keeping everything isolated is what should be done. But for average Joe homeowner, who would never think that there could be
240V between the two hots, I could see it happening.
It's not common in the sense that I've lived in many homes for many years and I have never seen one. And if you asked the average homeowner what an edison circuit or shared neutral is, virtually no one would have a clue. Yet, it's common for homeowners to replace a wall outlet or switch. If someone comes in this newgroup and asks how to do that, I've never seen anyone suggest to be careful, it may be an edison circuit or to verify that it's not being fed by dual breakers, perhaps not linked or correctly identified.
And the point is why do this? All that is being saved is one lousy, cheap neutral wire. I can see doing this if there is no easy way to do it otherwise, eg old work, but I would never do it for new work.
As to the dangers of this practice, here, from the DOE:
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They discuss that shared neutrals circuits pose unique dangers if not properly identifed and cite incidents that actually occurred. And this is for industrial settings, where you can expect skilled workers, not the average home, where Joe homeowner may be changing a switch. Now you could say, but that's because they were not properly identified. But why not just avoid it where possible all together?
It's not relevant whether the potential is 240V or not: if you've opened up a circuit for troubleshooting, that implies there is a fault somewhere. Possibly that fault is a short somewhere downstream. Allowing the two hot wires to touch will produce an arc; even 120V arc is plenty dangerous. If "average Joe homeowner" doesn't have enough brains to keep everything separated while he's probing voltage on live wires, he doesn't have any business touching the stuff.
I've never seen a kangaroo, either, but I understand that they're pretty common in some parts of the world. :-) -- the point being that it's sometimes a mistake to generalize from one's own experiences, without recognizing the limits of those experiences.
And I wouldn't be surprised if some of those homes had Edison circuits that you weren't aware of. :-)
The average homeowner doesn't work on his own electrical systems at all.
You're making the same mistake again: generalizing from limited experiences. I *have* seen that response here in this group, when someone went to replace an outlet and found black, white, _and_red_ wires when he was expecting to find only black and white, and asked what the extra wire was.
You haven't priced copper wire lately, have you? :-)
It saves not only a neutral but a ground as well. A piece of 12/3 has four wires in it; two pieces of 12/2 have six. A length of 12/3 is a *bunch* cheaper than twice that length of 12/2.
Voltage drop is reduced, which may be an issue on long runs.
It's also less labor to run one cable vs. two.
And it uses half as many Romex connectors in junction boxes.
It also reduces the number of conductors in each junction box, allowing the electrician to meet Code with smaller boxes (and possibly turning a non-Code-compliant overfilled box into a compliant installation).
Ditto for the number of conductors in conduits.
In other words, you're making hasty generalizations again... just because you can't imagine any reasons other than saving one neutral conductor, you assume that there aren't any.
Not a correct assumption, I'm afraid.
Then don't do it. But understand that your reasons for criticizing it are not valid.
Stop the presses! It's just been discovered that electricity can be dangerous!
Seriously, though -- _every_one_ of the incidents cited is traced to improper installation or documentation. You draw the same erroneous conclusion as the authors of the report state in the first paragraph: that shared neutrals are dangerous. This is not correct: the danger comes from improper installation. A properly installed shared neutral circuit is perfectly safe.
If it's been properly installed (using a two-pole breaker) it doesn't make any difference whether the guy changing the switch is "Joe Homeowner Who Barely Knows What He's Doing" or "Joe Licensed Electrician with Forty Years Experience in the Trade" -- flipping *one* breaker kills the *entire* circuit, just the same as with a normal 120V circuit.
No, it's because they were not properly *installed*, with a *single* means of disconnecting *all* of the hot conductors. And in at least one of the cases cited in that report, the energized neutral was apparently due to an incorrect connection to hot conductors -- improper installation again.
You're certainly free to avoid it if you wish. But to advise others to avoid it, on the basis of phantom hazards that you perceive largely due to your own unfamiliarity with it, is not logical.
Geez, you now think I'm so stupid I wouldn't recognize a double breaker in the panel? The only double breakers I have ever seen in my homes or other homes I've been involved with were for std 240V loads, ie dryer, stove, A/C. There were no other double breakers for shared neutral 120V circuits. If these were common, I would think you;d see a hell of a lot of people showing up in the newsgroup to ask what these double breakers were for every day. Yeah, one comes up once in a while, but if they were all that common, I'd be expecting them all the time, cause people would wonder what they had. I'd be interested in hearing from other folks as to how common they think a shared neutral circuit is.
Again, give me a break. It's very common for a homeowner to replace a switch or outlet themselves. Not all do, but for a guy claiming edison circuits are common and well known by everyone, it's pretty bizarre to be arguing that it's not common for a homeowner to replace a wall switch.
I don't think I'm the one who needs to do pricing. You can get 14/2 Romex for .20 a foot. 14/3 is about .30. So for a whopping 50 ft run, if you do it with 14/3, it's $15.00 for wire. Run two 14/2 cables and it's $20.00. Are you arguing that $5.00 is a big deal? Even if it were double or triple who the hell cares?
Can't a
Oh really, $5 is a bunch cheaper?
I never said there weren't valid reasons for doing it if you have to. In fact, I even stated, it could make sense for old work, where there is no easy alternative. And most of what you cited above, applies to old work, because in new work, the number or size of boxes ain;t a big deal. So, thanks for telling me what I already stated. Again, I'd like to hear from others that have seen shared neutrals commonly used in new construction.
Yeah, I new this was coming. The DOE is wrong too. The point is if it's easier to make something safer and easier to work on by not sharing neutrals, and it only costa a few extra bucks, some of us would prefer to do it that way. This is like arguing that hydrogen dirrigibles are safe, you just have to keep them away from lightning and use them properly.
The hazards are not phantom, but real andl documented and recognized by the DOE. But then you think they are wrong too.
That's because a double breaker is not required by NEC unless the outlets for the circuits are on the same yoke, such as a duplex outlet with the hot side tab removed and fed with a 12/3 w ground.
Then, no offense, but you probably don't do much new electric construction, because very few inspected electrical installations will pass unless the box fill is right.
As an electrician, I use them almost every day, especially in commercial and industrial work. In fact, try using one "neutral" for each hot on a commercial job and you'll get laughed off the job in a hurry, if not fired. The practice of using Edison circuits in residential wiring, IIRC, became common in the WWII era to save on copper. The practice is still common in residential wiring to this day. Now that the price of copper is though the roof there is no doubt that more Edison circuits will be used in new residential construction.
NEC doesn't require double breakers unless both circuits supply a common device. Using a double breaker is still prudent practice, but not all Edison circuits will have them. Hence it's fairly easy to be unaware of having Edison circuits unless you open up the panel and see the red wires.
Don't put words in my mouth. I never said they were well known by everyone. I contradicted your claim that they were a deviation from "what is common or expected."
IOW using an Edison circuit saves 25% on the cost of wire.
To anyone who actually does a lot of wiring, fifty feet is a pretty short run (not "whopping"), and a 25% saving on the cost of wire is important.
25% savings is a bunch, yes.
It makes sense for new work, too.
Nonsense. Conduit fill and junction box fill are considerations for *new* work much more so than old, because in old work the conduit and boxes are already in place.
Voltage drop and labor savings on running cable are equally issues in new or old work.
Actually I told you the exact *opposite* of what you already stated: that there are many valid reasons for using Edison circuits. Not my fault if you don't understand those reasons.
Read the article again. I think you missed the point in a few places.
Throughout, the hazards described are the result of improper installation and/or improper documentation of what was installed. The conclusion that the hazard is the type of circuit installed, rather than the acknowledged failure to install it correctly, is not supported by the evidence presented -- in fact, the evidence directly contradicts it.
You're still missing the point. A properly installed Edison circuit is no less safe to work on than any other circuit. You're perfectly free to not use them if you have trouble understanding them, but stop claiming they're less safe. They're not.
Poor analogy: a hydrogen dirigible is inherently unsafe in the presence of common hazards, whereas a properly installed Edison circuit is not.
Like I said, you need to read the article more carefully. The hazards documented there are hazards of improper installation and improper circuit marking.
ditto see it and do it all the time.Just did it in my spare bedroom {workroom} 4 hots 2 neutrals.pulled a ground but its not really needed ...its in pipe.Pig tail the neutrals at the outlets and good to go.
Hi, Kitchen couter top duplex receptacles have two separate circuit feeding each plug in. You have to break the link to separate those two receptacles to be fed separately. Wonder if mistake is made here.
That's because a double breaker is not required by NEC unless the outlets for the circuits are on the same yoke, such as a duplex outlet with the hot side tab removed and fed with a 12/3 w ground.
Do you mean by this that the top of the outlet would be powered by the red and the bottom of the outlet would be powered by the black. If not, I don't understand why you would need to remove the tab.
I asked my brother about this today and he told me about a discussion he had with an electrician a while back. The electrician told him that he sometimes does these circuits but "would always put the breakers on the 1 & 5 or some other combination so that you couldn't get 240V". My brother asked the guy about overloading the nuetral and the electrician told him "you don't have to worry about that as long as the breakers are good".
Yes, this guy was a licensed electrician that works residential construction. So I restate my opinion that I don't think it's a good idea because the next guy (weekend warrior) might only know enough to get himself hurt.
I wonder if he really does have a license... or just claims to. I used to live in a county that had *no* licensing requirement for electricians. Any idiot who wanted to, could call himself an "electrician" and go into business. Perhaps this guy is that type of "electrician".
Put it on a double-pole breaker, and it's perfectly safe.
And this is exactly the type of thing that lead to the incidents in the DOE report I cited, where shared neutral circuits were not IDENTIFIED, leading to people being shocked.
They're having a sale at the HD store 25 miles away for 25% off a $2 item. You're gonna save 25%, which is a bunch. Drop everything and get in the truck and go save your 50 cents. LOL Bet you can save another penny, by not putting staples in a cable on a job where it really should have one to be done right, but you figure it can pass anyway! Or save more by using the cheapest materials you can get away.
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