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In my home I have the old 3 wire Dryer and Range connections.

Looking at my CB service panel; my neutrals (white) and my ground wires (bare copper) connect to the same bus bar. Main service panel - this seems up to code for all intents and purposes (someone who is more knowledgeable correct me if I am wrong). I know secondary panels they must be separated.

So I have some questions here to enlighten me a bit more:

I have a Dryer and a Range Receptacles with the 3-Wire hookup (H-N-H) and I would like to make them 4 wire compliant (H-N-G-H).

I could run 4 wires back to the panel and connect my neutral and ground to the same location on the panel and of course the two hots to the hot lines.

What is the the difference doing that versus say connecting the ground lead to the neutral at the receptacle ? They end up at the same place. I know you should not do that; of course I know that people do this at the outlets in some homes to pass an inspection. I have had someone tell me - just connect the wire to a metal pipe .. but that smells bad to me..

While neutrals should not carry current - the possibility is that they can in a failure situation or a bad installation, so just having a separate wire go back to the bus bar and call it a 'ground'; how is that making a difference?

I was reading here What happens if you don't bond neutral and ground in a main service panel?

The answer does not clarify this for me exactly - it states advantages and disadvantages but never specifies exactly advantage / disadvantage of what .. (bonding in the service panel or not bonding in the service panel)??

I guess what I am really asking is how does it make it safer to have 2 wires go back to the same bus bar from the dryer receptacle and Why is it not safer to have a true separate ground at the main service panel where grounds are grounds and neutrals are neutrals ?

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    This may answer your question - in a typical 240V device, the neutral will carry some current since there are often 120V loads in the device (could be lights,motors, timers, control panels, etc) so some current flows back over the neutral. So if neutral+ground are bonded at the receptacle (or in the dryer), you'll be energizing the chassis if there's a neutral fault.
    – Johnny
    Commented Feb 26, 2018 at 7:44
  • @Johnny in 3-wire dryer if there is a neutral fault - the chassis is energized. also by touching dryer chassis and a ground or the washer (which is grounded) you can get electrocuted so I understand that; hence the reason for 4 wires. So from what I am gathering though is the 4th wire is just a redundant 'neutral' for all practical purposes ?? It might be a bare wire but it runs back to the same neutral bus bar.
    – Ken
    Commented Feb 26, 2018 at 10:19
  • @Johnny in the subpanel example neutral has fault current goes back through ground wire - everything works. From what I understand you don't run 4 wires to the sub panel but 3 wires (same scenario as a dryer / range) Subpanel chassis becomes hot in neutral fault. Your ground wire does not run back to main panel but to ground rod - so things do not work; as with that neutral broken you don't have a redundant path to the power station neutral line (probably a center tap of a xformer) and you know you have a fault condition because things do not work.
    – Ken
    Commented Feb 26, 2018 at 10:24
  • Neutral always carries current. Ground only carries fault current. You’re on the correct path when asking the question “what makes this safer?” Remember however, it’s the worst case scenario, a fault condition, that makes having a second exit path safer. Electricity returns to its SOURCE via ANY available path.
    – Tyson
    Commented Feb 26, 2018 at 12:10
  • The basic reason it is not code compliant to tie both the neutral and ground is that now objectionable current would be available on the grounding conductor, the grounding conductor is not supposed to Cary current under normal conditions. The neutral or grounded conductor is the return path for 120v loads. Since the 2014 code a separate ground can be run back to the service to add the grounding conductor so you can have a code compliant 4 wire outlet.
    – Ed Beal
    Commented Feb 26, 2018 at 14:20

2 Answers 2

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Neutral does and should carry normal currents

This may be the crux of your misunderstanding.

240V loads are carried on the two hots. 120V loads are carried on one hot and neutral. So a typical dryer might draw 20A of 240V and 3A of 120V. In that case the amperages of L1, N and L2 will be 23, 3 and 20. This is normal.

Ground is a safety shield only

The design philosophy of grounding is that grounds should never be used to handle current.

The circuit's overcurrent protection already protect from a fault between conductors. But what about faults between a conductor and anything else? That could cause a lot of mischief. Ground's job is to be the path of first resort for any wayward fault current. That works really well in metal-chassis machines.

"Wait. Won't GFCI do that same thing?" Kinda. Yeah. 30A 2-pole GFCI breakers can be had.

Neutral and ground should be separated everywhere except the designated Neutral-Ground Bond.

In an ideally wired panel, all neutrals land on the neutral bar, and all grounds land on the ground bar. There is a neutral-ground bond that can be removed.

This panel can be effortlessly converted to a subpanel by feeding it from another main and removing the neutral-ground bond.

It is also easy to measure ground fault current, by clamping a meter around the N-G bond.

However builders also have a lobby with the NFPA, and they lobbied for rules that let them spam it all onto one bar. It does no real harm, since they're connected anyway by the neutral-ground bond. It is leeeegal, just is a builder grade shortcut, and obviously prevents any of the things I mention above.

Why not bootleg ground on NEMA 14?

Well, that is what the NEMA 10 type hookup already does, so if that is your intent, there is no need to bootleg NEMA 14... you are already there.

It's back to the same problem as NEMA 10 and any other bootleg ground - any trouble with the neutral wire will result in the neutral being pulled up to 120V by loads, and with it the dryer chassis.

Whereas that does not happen if the neutral and ground are separated. In that case the machine just doesn't work and the ground continues to protect against hot-ground faults. Since there should be no neutral-ground faults, this becomes a non-event except the machine doesn't work obviously. The broken machine motivates the person to seek a proper repair.

If there was a neutral-ground fault, the machine may work normally misusing ground as current return. That is why bad repairmen create neutral-ground faults, to git-r-dun and onto the next job, safety be damned.

You can retrofit ground

Under NEC 2014 (and earlier for dryers) it is legal to retrofit grounds. You can run just a ground wire (#10) and retain use of the existing wires. It can go back to that service panel, or to any other ground also served out of that panel, as long it is of sufficient size (#10).

This same rule also makes a dryer ground retrofit useful for retrofitting grounds almost everywhere else, so it can be wise to plan it as a "backbone" for other ground retrofits.

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  • I had a misnomer on the neutral since GFCI works by an imbalance between [L1 supply- Neutral return]. It is a bit perplexing how faults travel the ground and not on neutral; reason I say this is that Neutral and Ground are tied at the panel. Just thinking (4-wire) internal to the dryer the "center tap - for lack of a better terminology" is isolated on the supply neutral line so things work when it is connected and don't when it is not. The ground line is simply attached to the chassis and isolated from any load provision [L1-G]; so if hot touches the chassis the breaker will trip.
    – Ken
    Commented Feb 28, 2018 at 1:06
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    @Ken on a 2-pole GFCI as you'd use on a dryer, it works on an imbalance among L1 supply, L2 supply and neutral return. That seems a little weird until you realize all current that goes out on any wire must return on some other wire. If you treat the return current as negative number, then L1 + L2 + N = 0. That is exactly what GFCIs do, they wind all 3 wires around a magnetic core in the same direction and the current flows turn into magnetic flux which cancels. If the magnetic flux does not cancel, it pulls a hammer down and trip.
    – Harper - Reinstate Monica
    Commented Feb 28, 2018 at 5:59
  • If I am to understand correctly running an additional #10 copper wire - I could just run this to the Washing Machine outlet ground connection so long as it is also a #10 ?
    – Ken
    Commented Feb 28, 2018 at 9:41
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    @ken yes, you could ground the dryer and switch to a NEMA 14 plug by running a #10 2 feet to the washing machine's receptacle, if and only if the washer ground wire is in fact #10. Sadly this is unlikely. However, any metal EMT, IMC or Rigid conduit counts as a ground path for #10.
    – Harper - Reinstate Monica
    Commented Feb 28, 2018 at 15:41
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It is difficult to understand to the layman. But you will just have to trust us on this one. It is safer to have two different conductors from the range and from the dryer, one colored white and one bare terminating in the same neutral bus bar in the service panel but it is true. It is not a waste of time and money. If they are bonded together at the appliance and for some reason the neutral comes loose at the panel the appliance body now would become fully and dangerously energized.

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  • So what you are saying is that if the neutral comes loose at the panel (or receptacle) the sole purpose of this is to put a redundant wire back to the panel ? I understand about the chassis becoming live - in a 3-wire Dryer this can happen when the neutral opens and with a 'grounded' washing machine next to it this can be bad. So I was thinking perhaps the house ground rod was truly "ground" and neutral was the 'ground' of the power plant ... am I missing something ?
    – Ken
    Commented Feb 26, 2018 at 10:07
  • Losing a neutral on a NEMA 10 is all kinds of bad all the time. It should not be tolerated anymore than is necessary.
    – Harper - Reinstate Monica
    Commented Feb 27, 2018 at 1:25
  • Like I said, It is complicated. It all started during the second world war when copper was scarce. Under these conditions the heavier conductor circuits were allowed to use the neutral to double as the ground. It was purely a matter of dollars and cents. Fast forward 60-years we want a high level of safety. As to your second point, it goes like this: the power company does not want to spend the money to give you the fourth wire. And as a result 'we' arbitrarily had to pick a place to establish the fourth wire. 'We' chose the service.
    – Paul Logan
    Commented Feb 27, 2018 at 16:52
  • @ken, (1) We protect against a hot wire shorted to the metal frame by providing a low conductance path back to service panel ground. This causes current to flow tripping the breaker on the hot wire and alerts you to the hazard. (2) We protect against an open neutral wire by separating neutral and grounding wires. Otherwise the frame can build up charge (capacitively, without a hot wire fault) and sit there waiting to shock you.
    – Stanwood
    Commented Feb 28, 2018 at 0:42
  • @ken (3) Neither has much to do with connecting the service panel ground to earth (e.g., by grounding rod). The connection to earth reduces the risk to life and equipment due to an external surge on the service neutral wire (e.g. lightning strike) by providing a decent path to earth. (4) If you would like to protect against a surge on the hot wires at the service entrance you need to install a dynamic load between hot and neutral/earth. This is what a Type 1 or Type 2 "whole house" surge suppressor does.
    – Stanwood
    Commented Feb 28, 2018 at 0:47

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