220V question

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

Reply to
Chris Eller
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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

Reply to
default

According to Chris Eller :

4-conductor circuits aren't "240V circuits" per-se. They're 240V/120V circuits. The only place where a homeowner would normally be concerned about four-wire circuits are stoves and dryers which need both 240V and 120V. US code now requires that new stove/dryer installations must be four wire, wheras it used to permit 3 wire. Canadian code hasn't permitted 3 wire stoves/dryers for several decades.

Pure 240V circuits (ie: 240W water heaters) are _still_ 3 wire. They don't need neutrals at all.

Sharing the neutral and ground _can_ be quite dangerous thing, that's why they changed the code and no longer permit it in the last remaining exception I'm aware of in the NEC.

Ie: if you have a neutral separation in the main panel, the frame of your stove _may_ go hot.

Reply to
Chris Lewis

According to snipped-for-privacy@uri.edu :

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.

Reply to
Chris Lewis

Maybe I am that guy! 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.

Reply to
Toller

...

interconnect

No, it's not you, but I suspect that was rhetorical, right? Too many people have been taught to look at these things from a voltage standpoint, (e.g. 0Vac = 0Vac = how you get it doesn't matter), instead of correctly considering current flow and direction plus fault control. I'll never forget my first encounter with ground currents: HOW could a wire overheat and melt, when there was 0V measured at BOTH ends of it? I watched 3 wires burst their insulation into flames before I figured it was a problem with me preventing knowing what went wrong! I was an avionics TS at North Island at the time. Of course, if I'd known to use the right meter scale, I'd have seen the voltage diff, but ... .

Regards,

Pop

It is comforting and speaks well of this group that such knowledge and participation exists here.

Reply to
Pop Rivet

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.

Reply to
SQLit

According to Toller :

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.

Reply to
Chris Lewis

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.

Sure they are the same wire on my 240 circuits; weren't you paying attention? Contrary to what you just said, my neutral is not insulated.

Reply to
Toller

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).

Reply to
ns

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

Reply to
Chris Eller

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.

Reply to
Doug Miller

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

Reply to
William Moss

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

Reply to
Chris Eller

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:

Reply to
Minnie Bannister

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.

Reply to
Doug Miller

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.

Reply to
Doug Miller

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

Reply to
zxcvbob

According to Toller :

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_.
Reply to
Chris Lewis

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.

Reply to
Chris Lewis

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