240V 3-wire drier ground/neutral confusion

[El_Cabrito]

I'm sure this has been posted to death, but i can't seem to find it doing a search. looking to setup an electric brewery of some kind, and i have an unused drier outlet in the basement. it has 3 prongs, so does that mean 1 hot (A), 1 hot (B), and 1 neutral (with ground tied to it)? if i want to use this outlet, do i have to add a ground somehow? i have seen spa panel additions after the outlet, but that appears to be for GFCI (which i would also need). Does this provide grounding? what is the way that is commonly used to get a ground on the current outlet? i own the house and am not looking to make a portable system. thinking 240V/30A with two 5kW element(s) switched.

Thanks!

 

[passedpawn]

That outlet does not have a safety ground. The neutral might seem connected to ground, but neutrals are meant to carry current, and that means the voltage on it at your rig will rise (and your entire rig will be at some elevated potential).

You need to add a safety ground, regardless of the GFCI setup you use.

By far, the easiest thing to do is to replace that outlet with a 4-prong. I can't tell you where to get the earth ground, but you could pull another piece of wire to that outlet from a ground somewhere else.

I know you might be tempted to run a separate ground to your rig, and continue to use the plug as it is, but that isn't any easier than doing it the right way, probably violates code, and isn't as reliable as doing it the right way.

 

[moparx12]

already answered

 

[Walker]

A NEMA 10-30 receptacle (3-wire, 30A, commonly used for a dryer) looks like this:

and is defined as a non-grounded 240V receptacle. It contains the two 120V hot lines and the neutral. The dryer has 120V items in it (buzzers, lights, etc) and those things use the neutral to carry current. The dryer's body is also 'grounded' via this neutral.

When you add the GFCI spa panel and plug that into the dryer outlet, what you are basically doing is splitting the neutral line into two lines. One of those lines is allowed to carry current (the one that passes through the breaker) and the other is not. The one that is not allowed to carry current is passed on from the spa-panel to your brewery to be used as a ground.

 

[Walker]

You need to add a safety ground, regardless of the GFCI setup you use.

Ultimately, the ground and neutral are tied together in the main panel, so the two wires really are the same thing. But, by using the GFCI spa panel to clone the neutral into one that is OK and one that is not OK to carry current, you create a wire that will sink current to ground and trip the GFCI if anything ever passes through it.

 

[P-J]

Walker,

Very well said and right on the money. Due to the fact that the line is terminated in a dedicated outlet, it IS according to code.

To the OP,

The GE Spa Panel from HomeDepot can be wired this way:

And it will fit the need very well.

Also: If wanted, a 4 prong dryer outlet can be installed directly in the Spa panel for the brewery panel if you want - like this:

Hope this helps.

 

[KitB]

Thank you so much for this post, p-j!
It prompted me to get off my butt & buy the spa panel.
With that diagram, it is so well simplified!

 

[El_Cabrito]

That's fantastic. thanks. i was hoping to not have to run a separate grnd line to the outlet from the breaker + this means no GFCI install in the main breaker either.

 

[passedpawn]

But, by using the GFCI spa panel to clone the neutral into one that is OK and one that is not OK to carry current, you create a wire that will sink current to ground and trip the GFCI if anything ever passes through it.

Clone the neutral? If there is no earth ground going to the spa panel, how do you "create" one? There needs to be an earth ground somewhere.

 

[Walker]

Clone the neutral? If there is no earth ground going to the spa panel, how do you "create" one? There needs to be an earth ground somewhere.

Look in your main panel. Neutral and ground are bonded together. Any where were you had connected something to neutral you have also connected to ground.

 

[passedpawn]

Look in your main panel. Neutral and ground are bonded together. Any where were you had connected something to neutral you have also connected to ground.

I'm well aware. Easier to ohm the outlet than remove the cover of my panel, but right.

If the OP has a 120 device in his rig, and he ties it to the neutral coming from the spa panel, how does that current get back to the panel? If it returns through the neutral to the spa panel, and that also serves as the safety ground, then the panels potential will rise when there is current on that neutral. It's likely that I'm missing something here.

 

[Walker]

I'm well aware. Easier to ohm the outlet than remove the cover of my panel, but right.

If the OP has a 120 device in his rig, and he ties it to the neutral coming from the spa panel, how does that current get back to the panel? If it returns through the neutral to the spa panel, and that also serves as the safety ground, then the panels potential will rise when there is current on that neutral. It's likely that I'm missing something here.

I guess I don't understand your concern maybe?

If neutral and ground are tied together all the way back to the main panel anyway... what's the difference?

 

[passedpawn]

I guess I don't understand your concern maybe?

If neutral and ground are tied together all the way back to the main panel anyway... what's the difference?

The OP asked if he needs a ground, I said yes, I was corrected. I'm all for the spa panel, but are you suggesting that there is no earth ground connected to it (only the neutral)?

 

[Walker]

The OP asked if he needs a ground, I said yes, I was corrected. I'm all for the spa panel, but are you suggesting that there is no earth ground connected to it (only the neutral)?

I am suggesting that neutral and ground are the same thing. If you have a 4 wire outlet and you start tracing the neutral and ground wires, they are both going to run side by side all the way back to the main panel were they are tied together.

The ground wire is not supposed to carry any current but the neutral does. I am suggesting splitting the neutral inside of a spa panel into two wires. 1 that is allowed to carry current and 1 that is not.

 

[Walker]

Oh and I was not correcting you. We were typing our responses at the same time. I had not even seen yours before I responded.

 

[passedpawn]

I am suggesting splitting the neutral inside of a spa panel into two wires. 1 that is allowed to carry current and 1 that is not.

I see.

Here's my point then:

• If there is a 120V device in the rig, the return current will return on the neutral feeding the spa panel
• Because there is current on that neutral, there will be a IR voltage rise at the spa panel and the rig; yes, the neutral is at ground potential at the breaker box, but not at the spa panel because of the current running on it
• The "grounded" rig, because it relies ultimately on the neutral that feeds the spa panel, will not be a earth ground but at this elevated voltage because the IR voltage.

Do you see what I mean? What am I missing here?

 

[Walker]

Okay so at my house my main panel is on the wall in the garage. I had a 50 amp outlet installed 2 feet away from it. That outlet is fed by a gfci breaker.

Neutral and ground are tied together inside that panel next to my outlet.

I don't see the difference. I am not trying to be a jerk. I just really don't see the difference.

There is a 4 wire outlet. There is a short run of wire. Ground wire connects to a bus. Hot and neutral go through a breaker. And athen neutral is connected to the same bus as the ground.

 

[passedpawn]

I brew behind my house, at least 100' from the breaker box in the garage. 240VAC. Assuming there is a 1 ohm resistance in the neutral wire, if used as a ground it would be at 10VAC if there was 10A running on it.

Sorry to split hairs, I'll go on my way now. Cheers!

 

[P-J]

I see.

Here's my point then:

• If there is a 120V device in the rig, the return current will return on the neutral feeding the spa panel
• Because there is current on that neutral, there will be a IR voltage rise at the spa panel and the rig; yes, the neutral is at ground potential at the breaker box, but not at the spa panel because of the current running on it
• The "grounded" rig, because it relies ultimately on the neutral that feeds the spa panel, will not be a earth ground but at this elevated voltage because the IR voltage.

Do you see what I mean? What am I missing here?

You are not missing anything at all. Yes the neutral potential will be elevated a very small amount above 'earth' due to the voltage drop caused by the current draw on the conductor. Is that ANY different than the neutral/ground supplied to the average dryer installed in a home with a 3 wire electrical layout?? Same thing with a free standing kitchen range powered with a 50A circuit before about 2004. We are talking about a voltage drop of less than 1 volt.

BTW - there is a greater voltage difference than that between earth at the power company's transformer and earth in your home.

Another thing for you to ponder. You live on a farm and there is a barn on the property. You provide power to it using overhead wiring. Is that power run through 4 conductors? (2 for phase A & B of the 240V + 1 neutral + 1 ground? Never happened.!!! It is a 3 wire system and earth ground is developed at the destination location.

 

[passedpawn]

BTW - there is a greater voltage difference than that between earth at the power company's transformer and earth in your home.

I've a copper stake near the power's entry point that ensure's that any standing water around my brewery is the same as the power ground coming into my house. It's irrelevant what the power company is delivering from the pole. Right?

 

[P-J]

Nevermind.. You are hell bent on your mission and free to go with it all.

Sorry to burden you with a possible thought process.

 

[passedpawn]

Nevermind.. You are hell bent on your mission and free to go with it all.

Sorry to burden you with a possible thought process.

I don't understand. The copper stake next to my breaker box ensures my breaker box is at ground potential, right?

I would like to understand. But you can take your sarcasm somewhere else. I did nothing to deserve that.

 

[Komodo]

If I may jump in and semi-hijack this with a totaly relavant situation. I can start a new thread if need be.

My shop has a dedicated 220 outlet that I'd like to use for my kettle using only one element at 3500 or 4500 watts. The shop is wired with regular Romex 12/2 (b, w, copper), and each outlet has a dedicated 20 amp breaker. I've purchased a 20 amp Payne Engineering phase angle controller I'll use for element control.

I've read about the spa panel thing, and understand about turning 3-wire into 4 with PJs diagram earlier. i'm still a little stumped on what I should do. I can get a 20 amp gfci for the main panel for not that much, maybe $70 or even less as my brother in law is a commercial electrician. And, from what I've read so far, I can install that on my current wiring. but that still leaves a 3 prong no ground? I might be able to rerun that single circuit with 12/3 as its not too far, but wonder if it's necessary? Is there a way to wire PJs diagram in the outlet, retaining the inwall wiring with a gfci in the breaker box?

I need no more than the 20 amps, only 240, no 120v to feed. I'd like to use twist locks, having a male socket on the keg element box, a removable power cable/controller unit, and plug straight into the wall.

Any and all help, suggestions are much appreciated!

EDIT: so, now as I read more about NEMA/plugs, am I wrong in understanding that using only one device on my circuit such as a 240v table saw or a 4500 heating element, the 3 wires are actually hot-hot-ground? And if my requirements are only one 4500 watt elemnt, I should be able to just swap out my receptacle for a 20 amp gfci receptacle or inline GFCI and be gfci protected, and grounded? Then I would need to find the L6-20 twist locks.

 

[Walker]

I brew behind my house, at least 100' from the breaker box in the garage. 240VAC. Assuming there is a 1 ohm resistance in the neutral wire, if used as a ground it would be at 10VAC if there was 10A running on it.

Sorry to split hairs, I'll go on my way now. Cheers!

see... now you have me all paranoid. I am going to have to sit and think about it. I see your point.

 

[RM-MN]

Electricity in the home was used for many years before outlets even had a ground terminal and then for several years more before GCFI was invented and very few people died from electric shock. We've been so conditioned to avoid any potential harm that we are willing to spend hundreds of dollars to have our homes rewired to meet current code without thinking how little risk is there. Yes a long neutral wire carrying current will have a small voltage to earth ground but could you even feel this small voltage, nevermind be harmed by it?

 

[Hermit]

I worked in appliance repair for a major appliance manufacturer. The neutral was always grounded to the cabinet. That said, there is a reason that the newer standards are calling for a separate ground. If running a separate ground is possible, go that route. If not, I wouldn't sweat it.

 

[Walker]

My shop has a dedicated 220 outlet that I'd like to use for my kettle using only one element at 3500 or 4500 watts. The shop is wired with regular Romex 12/2 (b, w, copper), and each outlet has a dedicated 20 amp breaker. I've purchased a 20 amp Payne Engineering phase angle controller I'll use for element control.

I've read about the spa panel thing, and understand about turning 3-wire into 4 with PJs diagram earlier. i'm still a little stumped on what I should do. I can get a 20 amp gfci for the main panel for not that much, maybe $70 or even less as my brother in law is a commercial electrician. And, from what I've read so far, I can install that on my current wiring. but that still leaves a 3 prong no ground?

If the wire running to your existing outlet has a bare copper wire, then that is a ground. You can drop in a GFCI outlet and not connect the neutral to the load side. You still have GFCI protected 240V, it just has no neutral available at the outlet.

I might be able to rerun that single circuit with 12/3 as its not too far, but wonder if it's necessary? Is there a way to wire PJs diagram in the outlet, retaining the inwall wiring with a gfci in the breaker box?

I need no more than the 20 amps, only 240, no 120v to feed.

In your case, I would install the GFCI breaker in the main panel and forget about the spa panel.

 

[Komodo]

In your case, I would install the GFCI breaker in the main panel and forget about the spa panel.

I've read through one hundred pages, and it seems like everyone is either using dryer outlets or needing 120v service for other stuff. So, I think I've been over thinking it.

So, 20 amp GFCI breaker in my panel>use the existing 240v (which is hot-hot-copper ground) NEMA 6-20R >#12 to my power controller (which is 240v)>#12 to the 4500 watt element and wired hot-hot and the ground bolted to the keg skirt. And I can use the regular NEMA L6-20 connectors, and will be grounded and GFCI'd?

I've also considered using this in-line instead of the breaker:
http://www.trci.net/products/shock-shield/user-attachables/in-line-attachable

And this is the controller, I have the 18D-2-20 (20i now, which has an isolated chassis):
http://www.payneng.com/PDFs/18depds.pdf

 

[Walker]

So, 20 amp GFCI breaker in my panel>use the existing 240v (which is hot-hot-copper ground) NEMA 6-20R >#12 to my power controller (which is 240v)>#12 to the 4500 watt element and wired hot-hot and the ground bolted to the keg skirt. And I can use the regular NEMA L6-20 connectors, and will be grounded and GFCI'd?

Yup.

I've also considered using this in-line instead of the breaker:
http://www.trci.net/products/shock-shield/user-attachables/in-line-attachable

I don't know much about those things, but I know they are cheap on ebay right now.

And this is the controller, I have the 18D-2-20 (20i now, which has an isolated chassis):
http://www.payneng.com/PDFs/18depds.pdf

Completely ignorant on those things. I am no help there.

 

[Komodo]

Completely ignorant on those things. I am no help there.

Thanks for your help. FYI, I was ignorant on those things too. They are phase angle controllers, mine is a soft-start with a 2-watt pot already on it. It has a small transformer that pulls 5 watts max for controls, it's fused with a big fat 2 millisecond fuse, and is built for exactly our application (heaters, replacing variable output transformers, furnaces, ovens, etc).

Mine is the older 18D-2-20, the newer 18D-2-20i has an isolated chassis. My heat sinks (built in) are electrically hot, so it must be mounted inside a box. I'm working on that now, or I think you may be able to swap out the old ones for the new ones for a small cost. Incidentally, I got mine unit Ebay for $35. New they are like $150. They also come in lots of different amp flavors.

 

[shelly_belly]

Look in your main panel. Neutral and ground are bonded together. Any where were you had connected something to neutral you have also connected to ground.

Is this the reason I get shocked whenever I touch the metal on my coffee pot and the sink at the same time?

 

[lschiavo]

Is this the reason I get shocked whenever I touch the metal on my coffee pot and the sink at the same time?

That is likely an ungrounded receptacle or improperly bonded water system. Maybe a short in the appliance.

 

[shelly_belly]

That is likely an ungrounded receptacle or improperly bonded water system. Maybe a short in the appliance.

Yes. The house was built in 1963. I can trace the receptacle ground back to the service panel and it has a grounding rod. How should the water pipes be bonded? Should they have their own grounding rod?

Thanks!

 

[lschiavo]

Yes. The house was built in 1963. I can trace the receptacle ground back to the service panel and it has a grounding rod. How should the water pipes be bonded? Should they have their own grounding rod?

Thanks!

Assuming metal water piping, the water line as soon as it enters the house should be bonded to the ground bar in the main panel. The water meter should be jumpered and hot and cold lines at the water heater should should be jumpered...to maintain bonding in case of dielectric unions.

Check that coffee maker. Without a grounded outlet, the metal case could be hot.

 

[shelly_belly]

Ha! Coffee maker has no ground. It only has a 2 prong plug.

 

[P-J]

Ha! Coffee maker has no ground. It only has a 2 prong plug.

Scrap it. You are playing you bet your life with it.

The power line is faulted to the coffee maker's case. It should be isolated from the case.

 

[lschiavo]

Probably good advice. And get some gfci's for your kitchen.

 

[chuckjaxfl]

Walker,

Very well said and right on the money. Due to the fact that the line is terminated in a dedicated outlet, it IS according to code.

To the OP,

The GE Spa Panel from HomeDepot can be wired this way:

And it will fit the need very well.

Also: If wanted, a 4 prong dryer outlet can be installed directly in the Spa panel for the brewery panel if you want - like this:

Hope this helps.

P-J,

In this spa panel, it looks like there's room for another breaker above the existing breaker.

Is is possible to install a 120V GFCI breaker in there as well, to provide protect power for pumps?

 

[P-J]

P-J,

In this spa panel, it looks like there's room for another breaker above the existing breaker.

Is is possible to install a 120V GFCI breaker in there as well, to provide protect power for pumps?

Yes, that can be done. Please keep in mind that you would also have to provide another outlet (120V) for the pumps. The other possibility is to run the 240V/120V power from the illustrated Spa Panel outlet to your controller box and split out the 120V circuits within the controller. (Protecting them with breakers or fuses within your controller)

Hope this helps.

 

[lschiavo]

P-J,

In this spa panel, it looks like there's room for another breaker above the existing breaker.

Is is possible to install a 120V GFCI breaker in there as well, to provide protect power for pumps?

Sometimes the buss is clipped. Pull the breaker out and make sure there is a stab to plug onto on the third slot.