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I have reviewed the answers and explanations about switching from 4 prong to 3 prong connections on a clothes dryer and grounds and neutral wires and the old way and the safer new way and the 240 volt phase shift that makes it possible to use the old (3 prong) neutral connection as a ground or substitute ground for the green wire when changing from 4 prong to 3 prong. I have a two part question which if I know the answer I think it will help me get the full grasp of this.

A) On the older 3 prong dryer outlet (NEMA 10-30), what is the neutral or ground connected to under the house (water pipe? nothing?)

B) On the newer 4 prong dryer outlet (NEMA 14-30), what are the 2 neutral/ground connectors connected to? (same water pipe? different water pipe?)

  • Electric wiring is done differently in different places. You should state where you live. – Stig Hemmer Dec 16 '16 at 10:28
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Neutrals, grounds, NEMA 10, NEMA 14, and the First Rule of Electricity

The old way (3-wire) is called NEMA 10, and abuses the neutral as a protective chassis ground. This works because the neutrals and grounds are bonded together in the main panel -- the purpose of a ground wire for an appliance is to send wayward current from the case back where it came i.e. the service entrance, while the neutral wire is going in the same direction, so to speak. However, the NEMA 10 setup is problematic because if the combined neutral/ground breaks, the dryer's chassis will then float off to some shocking potential.

NEMA 14 (4-wire) eliminates this problem by separating the neutral and the ground, making them take two different paths back to that main panel bond. That way, if the neutral wire to the dryer breaks or otherwise fails, the ground's still there to protect you from getting zapped.

When all else fails, remember the First Rule of Electricity: CURRENT FLOWS IN LOOPS!!! This means that electricity isn't ever trying to go to "ground", whatever-the-@$(!@$ that means, or to some random water pipe somewhere that really only is tangentially related to the entire electrical system. It's always trying to get back to where it came from -- your electrical service from the utility or the battery in your car, for example.

Think of it like some district steam plant -- the utility is only loaning you the electrons or water molecules, as they are mere carriers of the energy you're getting sold. Just like the steam utility would cut off someone who took all their valuable water and let it out into the atmosphere, the electric utility wants their electrons back just as much, if not more, and the same holds true for your car battery.

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It is helpful to look at the wiring chart for common plugs to understand what is going on.

enter image description here

An electric drier is 240V, 30A, so it uses the NEMA 10-30 connector. As the chart shows, there are two hots and a neutral.

This is a Really Bad Thing. Much of the time, an appliance wired this way (electric ovens are similar) will just work fine. However, if there is a wiring fault (e.g. short circuit), the chassis of the appliance can be electrically charged. 240V with 30A of current will kill you.

You should always upgrade the wiring rather than downgrade the plug.

Anyway, on to your specific questions:

A) On the older 3 prong outlet what is the neutral or ground connected to under the house (water pipe? nothing?)

The neutral is connected to the neutral bus in the main panel, which has a wire to ground (grounding rod or cold water pipe) and is also connected to the neutral entering the panel from the electric company. NEMA 10-30 has no grounding connector.

B) on the newer 4 prong outlet what are the 2 neutral/ground connectors connected to? (same water pipe? different water pipe?)

Both the neutral and ground are connected to the neutral bus in the panel.

However, the wiring on the appliance side is different. The neutral is used as a return path for any single-phase needs in the appliance. For example, perhaps the heater coil uses both hots, while the motor does not (not saying this is the case, just an example). There must always be a return path to complete the circuit, so a 120V part of the appliance would need that neutral (the 240V components just use both hots).

The key difference here is that with a 3 prong cable, the chassis is not grounded, while with a 4 prong cable, it is. This is why the chassis can be "hot" in a wiring fault with a 3 prong cable: there is nowhere for the electricity to go until you touch it and provide a ground. With a 4 prong cable, a wiring fault will take that path back to ground, hopefully tripping the breaker before you or a loved one touches it and possibly dies.

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Neutral Is Not Ground!

Seriously. They serve completely different functions, and should be isolated from each other entirely except in the one specific place they are bonded.

A lot of people have gotten into the bad habit of playing fast-and-loose with this. They wire main panels and jumble up neutrals and grounds on the same bus. They poach ground when they need neutral for a smart switch. Doing those things is arguable, but the line of thinking which leads you to them is wrong, dangerous, and has a body count.

Like ThreePhaseEel says, electricity wants to get back to source.

Neutral is the normal everyday current path for current to return to source.

Ground is a protective shield. It's used several ways, and the relevant one here is as a shield to protect humans from loose or misplaced "hot" wires. It should never, ever flow current normally. Any current moving on a ground is a fault condition.

Of course, current wants to get back to source, not to ground. Why does it flow down ground during a fault condition? Because as part of the design of this protection, we intentionally bond ground to source (neutral) inside the main service panel. Because of this bond, it is not wrong (merely sloppy) to have neutrals and grounds use the same bus in the main service panel. In ones way-of-thinking, they must be separated, and also in a sub-panel, they must be separated.

The history

In the beginning there was no ground, only neutral. You'd wire a dryer hot-neutral-hot and use a NEMA 10 connector. However there were a lot of electrocutions, and they were searching for a way to slow those down. In particular, equipment was mostly all-metal back then, and a fault between hot and chassis resulted in the equipment being energized at 120V. So the idea of a safety shield came up, to connect all the chassis to what exactly? Something that would safely take energy back to source, so they bonded neutral to ground at the supply, the transformer- or fairly near it, the main panel. (Since the transformer was usually up on a pole, hard to inspect, and the ground jumper is hard to protect from damage).

They then wanted to roll out "grounding" to American homes. They did this gradually, as renovations were done. However, the dryer and stove industry pushed back politically - they didn't want their customers having to spend $1000 to replace wiring in order to buy a new stove - it would kill sales! So they politicked to allow NEMA 10 to continue in service, on the logic that the plugs are rarely unplugged and dryers are rarely moved. They said "just ground the chassis to the neutral". Errmmmm...

How that fails with dryers and stoves

The problem is, if the neutral+ground wire has any kind of breakage, the hot wires will "pull up" the dryer's side of the broken wire up toward 120V. If the dryer chassis is bonded to the dryer's side of the neutral, that means its chassis is now energized. Touching that with rubber soled shoes won't kill you, but touching that and anything else, like the washing machine next to it, or the oven... Will!

As you would expect, this situation has a body count. It tends to be among the poor, so it's under-reported.

Grounding that dryer properly

I'm not going to trust my safety on a political compromise.

Obviously, hot-neutral-hot need to be connected in the usual way for the dryer to function.

A huge safety win is to put the hot-neutral-hot onto a GFCI breaker. I would be confortable continuing a NEMA 10 in service in that situation. It would protect from any sort of current leakage.

Otherwise I would properly retrofit a ground, which is now legal to do. It can follow any viable route back to the same panel. Then use a NEMA 14 receptacle (which the dryer probably comes with) so you are paying to replace the receptacle instead of the dryer cord.

Or I would hack the dryer to be 240V-only and not use neutral at all, by internally adding a small transformer to power whatever it has that is 120V. (Probably the timer and controls, maybe a light bulb). This isn't that weird; this is exactly what the manufacturer does when they sell the same dryer in 240V/60Hz territories like the Phillipines. In fact I would just use OEM parts if available. At that point I'd use a NEMA 6 connector (ground, no neutral) and (illegally) re-task the old "neutral" to be a "ground" by marking it with green tape and moving it to the ground bus.

Or if I was poor, I would hack in a proper ground any which way I could, i.e. To a nearby water pipe in an all-metal pipe system... not legal but better than nothing.

  • If the NEMA 10 circuit was installed with SE cable, then the neutral was bare to start with -- and retasking it to be a ground would be a compliance improvement, not a violation. P.S. why in the world couldn't they make a 240VAC-only dryer back in the 1950s? – ThreePhaseEel Dec 16 '16 at 23:40
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A) On the older 3 prong outlet what is the neutral or ground connected to under the house (water pipe? nothing?)

B) on the newer 4 prong outlet what are the 2 neutral/ground connectors connected to? (same water pipe? different water pipe?)

None of the wires in an outlet "connects to any pipes" (At least not physically directly.)

In your breaker box there are bus bars for ground and neutral. If it's a main box they are the same and can be mixed.

bus bar

The neutral (white) and earth ground (bare copper) wires both go to bars like this in your panel (box). In a sub-panel they are separate, they both feed back to the master (main) panel.

In the master panel, the neutral/ground bus bars are connected to the same metal you would touch on the door of the panel for instance.

In the master panel, there's an incoming neutral from the power company, and there's one or more thick copper grounding wires that connect to buried grounding rods, or water pipes, or some other ground.

There may also be grounding wires that connect to other places including any large metal structures in your home, but that is not related to your question.

All of these connect to the same bus bars in the main panel.

So the ground and neutral of any outlet should conduct through to the panel (box) but it eventually winds up at a ground rod or metal water pipe pipe. It does not run from each outlet to any old water pipe nearby! (unless it was put together by a drunken sailor)

  • that conveys a dangerously wrong message, you're talking like neutral and ground are the same thing and can be connected to the same places whatever They are different things with different functions and it's intensely important they be bonded only at one place. – Harper Dec 16 '16 at 19:13
  • Nothing in it is wrong with the message. It did not say that neutral and earth safety ground were "the same thing". – Billy C. Dec 16 '16 at 21:15
  • Not literally. But my point stands, that your message does next to nothing to show why ground and neutral should be separate. You use the confusing term "grounded conductor" and show a "grounded" bar with both grounds and neutrals on it. You don't make clear what happens in subpanels. Your last paragraph again talks as if grounds and neutrals go to the same place "through to a water pipe", see where that's confusing? While you can justify each statement and an electrician will say "I see what you did there", it would confuse a novice badly. Hence my suggestion for some work. – Harper Dec 16 '16 at 22:06
  • The question was "where the wires go", not "how does safety grounding work and please also throw in a novel about subpanels". I was tempted to joke that ground connects to the cold water supply from the city and the two hots connect to the two sides of the water heater but it sounded like he/she might actually believe that. Sometimes less is more. This is one of those times. – Billy C. Dec 16 '16 at 22:12
  • Good point, less is more. Yours is more fixable than mine, so here's an edit. – Harper Dec 16 '16 at 23:58
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Under normal conditions neutral and ground should be at roughly the same potential. They should be connected to both the general mass of the earth through grounding rods and to the neutral point of the supply transformer.

Trouble is when trying to design a safe electrical system we don't just have to worry about normal conditions we also have to worry about what happens under fault conditions.

The ideal is for the neutral and Earth to meet at exactly one point. This is safe under "single fault" conditions. If the neutral breaks then things will stop working and some equipment may be fried by overvoltage but there is no real shock risk. If the Earth breaks then we have lost it's protection but we hopefully don't have an immediately dangerous scenario.

If the neutral and earth functions are combined in the same wire (or even with seperate wires the devices have a large earth leakage) then a disconnection of that wire makes the downstream devices live. This is a BAD thing.

Different countries at different times have had different ideas on to what extent it is appropriate to combine the two roles and what additional precautions should be taken when doing so.

AIUI current practice in the USA to combine the functions in utility wiring supplying houses and on the busbars of the customers main panel but after the main panel they must be seperated.

Older practice also combined the functions on distribution circuits to subpanels and on supplies to large 120/240V appliances like cookers.

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To answer your questions. Both a three and the four wire outlet. Do not hook up to the water pipe. They must go to the panel. And the dryer outlet. If it is the main panel.Both neutral and ground can go on same bar. If it goes to a sub-panel. Neutral goes to neutral bar. Ground goes to ground bar. On a four wire outlet. Without a lot of input. If you have three wire . Two hots and one white. If it is in emt could use emt as ground. Or add a ground wire if you want. Three wire in old work still code . If you can upgrade you should.

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I am an electrical contractor from the UK where residential power is 240v 50 hertz between neutral and hot. The ground (earth) is absolutely essential to carry any fault current back to the panel. When I arrived in the US some 40 years ago, I was amazed at the neutral/ground being tied together on the dryer and range situations. I tried to get the NEC to consider separating these for future installs. But with no success. I was also amazed at the disposal/dishwasher circuits being tied into two single breakers at the panel and not having a 2 pole breaker tying both circuits together off one handle. Turning off one single breaker on a shared 3 wire circuit leaves the other side hot in the box, (particularly on a disposal/dishwasher). I still think this is not good practice and really doesn't cost anymore to tie both circuits together (2 pole breaker). Just a view from an old electrician.

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The 240v appliance sees both 120v taps from the transformer. When only one of these taps is used for 120v appliances, computers, etc., the neutral serves as the return, and the ground protects against potential energizing of the appliance, computer, etc. in a fault condition. When both 120v taps are used as hot for 240v appliances, the neutral (center tap) is not required at the wall socket/plug connection. The earth ground connection to the chassis of the 240v appliance--via the panel--where both neutral and ground meet, eliminates a potential ground loop when the unnecessary neutral connection ends at the bus in the panel.

  • Hello, and welcome to Stack Exchange. While interesting, this doesn't really answer the original question. – Daniel Griscom Feb 7 '18 at 2:04
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I think simple on 3 wire outlets. If a hot line touches the frame...you bet I want neutral as the frame ground...the alternative is my body to ground. The flipside is the lower risk of becoming a better return path than neutral or a shock. I think this is what NEMA exception is, a lesser of two evils when 4 wire isn't there.

Wonder where this electricity wants to return to where it came from seminar is? It's simple, path of least resistance to lowest potential. It has no memory, it just naturally moves to a lower state. Lightning, Ground Conductors, Waterfalls, Your Fluke battery dying, LIFE etc..

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