220V question

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Hello all. Just a question about 220V wiring for you. I've encountered several 3-conductor 220V circuits recently. Doing a little research, I see that around 1965 or so it was changed to requiring 4-conductor to seperate the ground and neutral (vs. the old two hots and the third wire being both the ground and the neutral).
Am I correct in the above? (may only be residential NEC stuff).
Does anyone know if having the neutral and ground share a conductor is a bad thing? Does having a seperate ground really help with safety? Is some equipment effected by the N/G binding, or a seperate N and G?
Thanks in advance!!
Chris
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The three-wire cable did not "combine" the neutral and ground, the three wire cable HAD no neutral. 220V has no neutral, it uses two 110V wires of opposite polarity. The fourth (N) wire is for modern equipment that also has 110V circutry in it.
Yes, it is both dangerous and forbidden to combine or interconnect the two.
Is it just me, or do we get this question every day?
--Goedjn
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Just about. Worse, it's the same guy telling them that neutral and ground are the same thing every time.
I need to get the FAQ updated and into autorepost.
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Chris Lewis, Una confibula non set est
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The 240v circuits to my A/C, oven and dryer have two hots and an "uninsulated neutral" (some manufacturers call it a "bare neutral". Say what you what, that is the official designation. And of course, it is attached to the chassis, so it is also the ground. Every house on my street, and millions of others, are wired identically. What is the last time you heard of a problem with it?
The ground and the neutral aren't the same thing, but they are the same wire.
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I just bought a new maytag dryer they tried to hand me a 3 wire plug. I nixed it they said it was just fine. I said if they want to complete the order get the right part. They did and all is well. My new home circa 1999 has four wire even for the water heater. Which was good when I connected the time clock.

If there was not a problem with it why was it changed. Every time you use a ground as a neutral you ask for problems. Granted it does not happen very often. But it does happen. The industry has learn a few things in the last 30 years and all that the NEC does is set a mininum standard. When followed the installation will be safe for all concerned.

Excuse me, No they are not. A ground is a non current carrying conductor most of the time. A neutral carries current and voltage. That is why it is insulated all of the time a ground can be both insulated or bare.
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So you say, but cite an incident. I know the problem is that if the neutral connection at the breaker box opens, the chassis is potentially hot. Aside from being unlikely (what is the last time you had a neutral connection at the breaker box open?) it is dumb. If the chassis is hot, it is because there is an open circuit. If there is an open circuit, the appliance will not be working. So, you have to have an open neutral, not notice the appliance is not working, and be well grounded (since you will be in series with the appliance.) Sure, with 50,000,000 such circuits out there, there is probably a problem now and then, but you probably have a bigger risk of being hit by lightning.

attention? Contrary to what you just said, my neutral is not insulated.
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You are a fool to play with such odds. The NEC is there to reduce the chances of you getting hurt in the case of a fault.
The combined ground/neutral can open anywhere, not only the breaker box (surely you heard that every so often someone loses their phone connection, water mains or gas line bursts - these happen because either the earth moves or some cuts into them. The same can and does happen to wiring in the house. Just check some of the safety standards UL published in the last 100+ years).
You don't need to be well grounded, just sufficiently to allow ~50 mA to pass through your body and start giving you trouble. People not always pay attention to how and if appliances work when they operate them, not every person on this earth is mechanically or electrically inclined - that is why they write all those 'XXX for Dummies' books.
You may have a circuit in your home that has the ground and neutral using the same conductor. If undisturbed, this is still acceptable (knob & tube, asbestos, UFFI, etc come to mind - if left alone are OK).

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Five years ago in my previous house. The neutral for my dishwasher was loose at the breaker box. It prevented the dishwasher from working at all for several years until I got around to looking into it.
Next Question?
William

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Do google searches on this group and misc.consumers.house. I remember seeing at least 3-4 confirmed open main neutrals leading to extremely strange problems being reported and discussed.

Incorrect. If the main neutral opens, 240 devices (ie: stove elements) won't notice a thing awry. If the load on the two legs is roughly equal, the 120V devices will continue to work _too_.
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Chris Lewis, Una confibula non set est
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Evidently the NEC heard of enough to change the practise.

Not anymore. NEC now forbids that practise in new construction.
CEC hasn't permitted it for at least 3 decades.
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Chris Lewis, Una confibula non set est
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Lots of good information in here (and some good/bad opinions).
Related then is the following; my house was built in 1965 and uses a bonded G/N for my 110/220 outlets (stove to be precise). Everyone seems to agree that a seperage G and N are a _good idea_, and I agree with that. Is it worth it to run a new 4-conductor line to my stove for such a refit?
Something that may make this a moot point; mt main electrical box has bonded neutral and ground bus-bars. So, any improvements I make up the line won't really help as the box is old design. Probably have to replace the box as well.
An I on target here?
Thanks in advance, Chris
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No. Your main panel is just fine. The NEC *requires* the ground and neutral bars to be bonded at the main panel, and *prohibits* *any* connection between ground and neutral anywhere else.
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Definitely good to know. What I really need to do is take a few classes and learn to not only read, but _understand_ the NEC. :)
As I understand it, the NEC changed the bonded N and G around the time my home was built (1965), so somehow my stove was wired up with three conductor: H,H,N/G. Would you say that running a new 4-conductor (H,H,N,G) line to the stove would be beneficial? I certainly think it would be an improvement, but is it necessary?
Thanks, Chris
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Does your stove have any 120V elements (clock, timer, pilot lamps to show when things are on, etc)? If so, then it would definitely be a good idea to run a new cable. If not, then there is no need -- the neutral is used only by 120V circuits, and not by 240V circuits.
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Chris Eller wrote:

Let's review what happens when the neutral goes open at any point in the circuit between the panel and the stove. The stoves 120 volt loads will serve as rather low resistance conductors between one of the ungrounded conductors and the frame of the stove. Another poster has alleged that that is not a problem because you will be in series with the load. When two impedances are in series the largest quantity of the voltage will be reflected across the higher impedance. In the circuit in question the higher impedance is the human being. If the voltage applied across that human being is higher than 30 volts there is a likelihood that that person may be injured or killed the only thing missing is contact with another conductive surface that happens to be grounded. The kitchen sink, refrigerator, dishwasher, and even many kitchen floor coverings are sufficiently conductive to provide that conductive pathway.
It has also been alleged that it makes no difference because both conductors terminate on the bonded buss bar of the service equipment enclosure. That position ignores the fact that since the neutral conductor carries current it expands and contracts with each use of the appliance. As a result of that normal thermal cycling it's connections are under far more stress than those of the equipment grounding (bonding) conductor.
In the older three wire configuration any failure of the neutral conductor energizes the frame to the potential of the circuit. In the four wire configuration the neutral opening causes the appliance to stop functioning but the frame will remain at zero volts relative to other grounded surfaces.
I'm only one member of the entire nations fire service and I have attended three accidents that were secondary to failure of neutral terminations on three wire appliances. It is true that I have been in active service for thity plus years. One was an electrocution. the other two were electrical injuries that were short of being fatal. One was a working code who then spent weeks in the hospital and was provided with an implanted defibrillator while her injured heart muscle healed. The other suffered a dislocated shoulder and a fractured arm as a secondary effect of the severe muscle contractions that occur during electric shock. In all three cases the appliance in question was an electric clothes dryer were the frame was bonded to the neutral.
It is your house and your family so which one do you think is better. -- Tom H
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Generally an excellent post, but I think this bears commenting on:

The problem with 240V/120V appliances is that if you lose the neutral, the appliance doesn't necessarily "completely" stop working. Regardless of whether it's 3 or 4 wire attached.
For example, with most stoves, if you lose the neutral, the only likely symptom is that the clock stops working (but it won't necessarily![*]), yet, the cooktop and oven continue working. Because they don't use the neutral.[+]
Similarly, with a dryer, the heating elements will continue to work, but the drum and blower will stop operating.
With a stove, you may not even notice that this has happened - the stove still cooks dinner. With a dryer, if you're not there to notice (or, you think it finished it's cycle), you won't notice.
In and of itself, losing the neutral for a stove is harmless. With a dryer, you may well end up having to rely on the thermal cutout preventing a house fire.
Furthermore, if the stove or dryer is on a three wire connection, the frame now becomes directly part of the circuit - if you touch a better ground (like a faucet), you can get zapped by the unbalanced current flowing thru the clock (or drum rotator motor or timer motor on a dryer).
At least with four wire, you have a vastly better chance of the frame _not_ becoming part of the circuit and you won't get zapped by the clock.
[*] the clock may continue to function but _only_ during the times that the elements are powered up. On a dryer, the timer/motor may "work" (possibly very badly or not at all with black smoke) when the elements are powered up. Depends on where the break is.
[+] I encountered a similar situation. In reverse. I helped rewire a friend's house. They had to live in the place during renovations, so, there was always being work done. Got a call several days after I installed (and tested) a new 4-wire stove circuit with the complaint that "the clock's working, but nothing else is". After much head-scratching, I managed to figure out that my friend had removed and reinstalled the duplex breaker for the stove (because he was adding something else). This particular panel (a FPE) alternated legs in _pairs_ (AABBAABB) not individually (ABABAB) and he had reinstalled the breaker such that both breakers were on the same leg. _Both_ ends of the heating elements were attached to the same leg, so the elements didn't work. But the clock was quite happy.
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OK, here's one for you:
Our previous house had a 4-pin outlet for the dryer, but our present one had only a 3-pin outlet, so I replaced the dryer cord by a 3-pin one (and moved the green wire at the connection block, according to instructions).
But we have subsequently stacked the dryer and the washer, so everything now has a "real" ground through the washer's power cord, right? (And doesn't that mean that the neutral and ground are now connected at a place other than the main panel?)
Would there be any advantage in replacing the 3-pin dryer outlet by a 4-pin and replacing the 4-pin cord?
MB
On 04/20/04 08:09 pm Doug Miller put fingers to keyboard and launched the following message into cyberspace:

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Upgrading the circuit would have been a better idea than downgrading the appliance.

No, not unless you also installed a bonding jumper from the frame of the dryer to the frame of the washer. Simple contact between the two cases is not enough to ensure a solid electrical ground.

Might be, depending on exactly what you did at the connection block in the dryer -- and if so, there's a potential for the dryer case to become energized. That's why it would have been better to upgrade the circuit to 4-wire.

Yes, there would: you ensure that no matter what happens, the case of the dryer will *always* be at zero potential with respect to earth ground, and thus incapable of delivering a shock. That's what the safety ground system is for.

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Minnie Bannister wrote:

No. Your dryer has 2 hots and a ground and no neutral. An exception in the old code allowed you to use the ground for the unbalanced portion of the dryer load (for the timer, buzzer, light, and maybe the motor). Your washer has a hot, ground, and neutral, and its neutral is isolated from the frame.

I would leave it alone. I assume you know you cannot just replace the outlet unless you run a big (probably #10 copper) neutral wire? This means running a whole new cable to the dryer, unless the wires are in conduit. If you're willing to rewire it properly, it would be marginally safer to have 4 wires. But not much safer as long as the neutral connections are good and tight in the 3-wire hookup.
Best regards, Bob
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Most dryers have 120V motors and timers, so they "need" neutrals.

Here's something that may put this into context:
If I understand the NEC rules maze correctly, if you move into a house that has a three wire stove connection, at most, NEC requires you to put a receptacle on it. You do not have to upgrade to four wire. Which is why both 3-wire and 4-wire receptacles and stove/dryer plugsets are available, and why stoves and dryers are convertible.
In contrast, by CEC rules, if you move into a house that has a three wire stove connection, not only do you have to install a receptacle, you must upgrade to 4 wire. Which is why three-wire stove/dryer plugsets are _not_ available here (and three wire receptacles only available for non-dryer/stove applications - pure 240V only - you can't feed a neutral on a 3 wire 240V circuit).
[For compability with US standards purposes, most of our stoves and dryers are convertible too, but it's specifically not listed in the instructions, or there are disclaimers it doesn't apply to Canada or covered by the generic "consult your local code!" fine print.]
The NEC doesn't think the risk is high enough to require 4-wire upgrades to 3-wire systems. The CEC does.
The NEC doesn't think the risk is high enough to require mandatory refit on existing installations (except for new work). The CEC agrees here.
Whether you want to go to the upgrade-to-4-wire CEC rules is something you have to answer for yourself.
I would think there's a _slightly_ increased risk with stacking a ground-neutral bonded appliance with a ground-neutral separate appliance. But minimal at worst.
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