Supplying power -- 3-prong range outlet?

[P-J]

Any additions must conform to current code. If the house wiring had to conform to current code when a wiring addition was done, most houses in this country would have to be rewired when something was added. And adding this spa panel to a unused stove circuit is adding to existing wiring.

Well said.

Just another prospective: If the Spa panel is installed as a plug in device, the building wiring is not altered at all. Therefore no inspection required and no violation of any code.

Almost every dryer or range is a 240 + 120V device. Through about 2007 the power feed was done using a 3 wire feed.

Just saying.

 

[thargrav]

So the spa panel, going from 3 wires to 4, would conform to the current code? I thought not, because are not neutral and ground bonded together in the spa panel? I was not referring to the preexisting wiring.

That's exactly what this panel is - it converts a non-protected 3 or 4 wire circuit into a GFCI protected 4 wire circuit.

 

[petey_c]

As thargrav said you could change the 2P50A breaker (if you feel comfortable doing so) to a 2P30A and the circuit would be protected at 30 amps and use the spa panel for GFI protection.
In some of the old 240 VAC installations they used SEU cable (two insulated conductors and one un-insulated). The current in the two legs balanced out and the resultant current was just about zero. I don't think you can use the "neutral/ground" (bare conductor) wire for 120VAC circuits, because it becomes an un-insulated current carrying conductor which is a no-no. You'd have to convert the other conductor to the neutral and use the bare wire as a ground.

 

[thargrav]

The third conductor in the SEU cable, which is the braided cable wrapped around the other two, is intentionally sized large enough to handle quite a bit of current. "From memory", if aluminum, the two main conductors are 6 gauge and the braided wrapper is 8 gauge. Also, because of the outer covering, the braided part is considered an insulated current carrying conductor. It's also the safety ground for the stove.

 

[whoaru99]

I wouldn't think of the neutral as a ground. When there is a lot of current running through it, there might very well be an AC voltage present (I*R drop across poor connections or wire resistance).

Also, if there is a GFCI upstream on the ckt, the neutral isn't directly tied to earth ground anyway. You might not always know if the ckt is GFCI protected.

Green is ground. White is neutral.

The tems I used previously are accurate.

By NEC, the official term for the "neutral" is grounded conductor, and the equipment/safety ground is officially called the grounding conductor.

These terms are used by NEC to avoid ambiguity.

 

[whoaru99]

almost every dryer or range is a 240 + 120v device. Through about 2007 the power feed was done using a 3 wire feed.

Just saying.

1996.

 

[passedpawn]

The tems I used previously are accurate.

By NEC, the official term for the "neutral" is grounded conductor, and the equipment/safety ground is officially called the grounding conductor.

These terms are used by NEC to avoid ambiguity.

Hmmm. I don't think that's a good way to avoid ambiguity. Grounded conductor, grounding conductor.

But I do believe you. Thanks, I learned something tonight!

 

[whoaru99]

That's exactly what this panel is - it converts a non-protected 3 or 4 wire circuit into a GFCI protected 4 wire circuit.

It doesnt really convert anything except adding the GFI (which I fully agree is good). Merely adding a GFI does not allow you to make equipment grounding from the neutral (grounded conductor).

 

[whoaru99]

Hmmm. I don't think that's a good way to avoid ambiguity. Grounded conductor, grounding conductor.

But I do believe you. Thanks, I learned something tonight!

Its certainly much better than just plain "ground", which as you read these threads, is used loosely for any number of things, whereas grounding wire means one thing and one thing only.

 

[thargrav]

1996.

Every range and dryer sold today is setup for three wire or 4 wire because they have to be compatible with houses wired before 1996. And just about every dryer and range sold today has a mix of 120V and 240V components.

In a dryer - the heating elements are 240V, the controls may be 240V or 120V, the motor may be 240V or 120V.

In a stove - the oven light is 120V, the controls can be 120V or 240V.

 

[ajdelange]

That's exactly what this panel is - it converts a non-protected 3 or 4 wire circuit into a GFCI protected 4 wire circuit.

This diagram troubles me. At the left we see Ground/Neutral coming in. There is no ground/neutral. It will be either ground (earth/grounding conductor) or neutral (grounded conductor). The only place these are joined (and allowed to be joined) is at the service entrance. The ground wire is there to ground equipment, IOW to be sure that the frames of all equipment connected to the system are at the same potential - earth potential. That is its sole purpose unless there is a frame to hot or frame to neutral fault in which case it serves as a return path for the fault current as opposed to a path through someone who touches the frame. Sticking with the case where the 3rd wire is ground/earth one can 'convert' to 4 wire by installing a center tapped transformer in the 'box'. The neutral connects to the center tap. One may not 'derive' a neutral by connecting a white to the ground wire. To do so violates one of the fundamental tenets of the code: the ground wire is not to conduct load current - only fault current. If the loads on the 120V circuits are equally balanced (as is a single 240 heater element) then the loads on the red and black legs are perfectly balanced and there is no current in the ground wire. This is why true 240 only loads are wired with red, black and green. If you connect any 110V load between a hot (Red, Black) and the ground wire the return current from that load will flow back to the panel through the ground wire thus violating the code. Saying that you are not violating the code because you are doing this with something that plugs in and consequently does not, therefore, change the house wiring is fooling yourself. It certainly violates the spirit of the code if not the letter. No 'appliance' that took 120V from a hot, hot, ground branch would get UL approval.

Now lets suppose the three wire circuit is hot, hot, neutral. You certainly can take 120V from that arrangement but what about the ground/earth connection? It isn't available. If you connect the neutral (white) to the frame of an 'appliance' which is one of the few excepted from the requirement to have a separate ground by the code (dryers, ranges and ovens) then you are grandfathered in if the house was wired H/H/N before a certain date. Hooking a green wire to the white wire in a spa panel is not covered by the code and does not 'convert' the system to 4 wire and you are fooling yourself if you think metallic equipment connected to that green wire is properly grounded. It isn't. It may be better grounded than if it were allowed to float but it will be at other than ground potential if there is any asymmetric load (including a fault). A few mV are not a big deal with a clothes drier but when conductive liquids are around it's a different matter. Note that hot to pseudo ground leakage should cause the GFCI to trip if the connection to the neutral is made before the GFCI but not if made after. Also note that in the case of asymmetric load with connection after the GFCI the G-N circuit will trip the breaker if the pseudo-ground has a path to true ground (the N-G detection current loop is from the injection point on the neutral at the GFCI to the neutral P-G connection, through the leakage path to earth through the earth to the service entrance N-G bond and back down the neutral to the injection point). The voltage induced by an asymmetric load (no fault) would not trip the breaker

One would have to run a separate earth wire from the panel or sink another ground rod somewhere near the spa panel (and I'm not sure what the code would have to say about either of those) in order to get a true 4 wire system.

I've certainly not researched spa panels extensively but all the ones I have looked at expect a 4-wire connection to the panel. The reasons for this seem pretty clear to me. Can you get something that 'works' with a three wire connection to a spa panel based on the asymmetrical parts of the load being small compared to the symmetrical? Yes. Is it safe? Not so sure. Is it kosher? Probably not.

 

[passedpawn]

One may not 'derive' a neutral by connecting a white to the ground wire. To do so violates one of the fundamental tenets of the code: the ground wire is not to conduct load current - only fault current.

Right. The exposed metal on the appliance will be at a I*R potential if the neutral is used; 'I' can be substantial, and 'R' is variable depending on a bunch of questionable connections.

I used to get shocked by my toaster oven; I suspect its body was "grounded" to the neutral.

 

[thargrav]

Right. The exposed metal on the appliance will be at a I*R potential if the neutral is used; 'I' can be substantial, and 'R' is variable depending on a bunch of questionable connections.

I used to get shocked by my toaster oven; I suspect its body was "grounded" to the neutral.

If you live in a house that was built before 1996 your stove and dryer are wired exactly like the left side of my drawing - with three wires - and the ground / neutral (they are shared on the same conductor) run back to the power panel along with the two hot leads.

And you are worried about exposed potential on the outside of your stove or brew rig?

The resistance of #6 wire is 0.618 ohms per 1000 feet. And I doubt if the run from your power panel to your stove is more than 35 feet which would be a whopping 0.02163 ohms. So, even if the ground conductor were drawing all 30 amps, and it won't be, the voltage would only be 0.6489 VAC!

That's less than the voltage from one flashlight battery!

 

[jeffmeh]

Now I don't feel so badly about being confused on this point.

 

[passedpawn]

If you live in a house that was built before 1996 your stove and dryer are wired exactly like the left side of my drawing - with three wires - and the ground / neutral (they are shared on the same conductor) run back to the power panel along with the two hot leads.

And you are worried about exposed potential on the outside of your stove or brew rig?

The resistance of #6 wire is 0.618 ohms per 1000 feet. And I doubt if the run from your power panel to your stove is more than 35 feet which would be a whopping 0.02163 ohms. So, even if the ground conductor were drawing all 30 amps, and it won't be, the voltage would only be 0.6489 VAC!

That's less than the voltage from one flashlight battery!

There are other known, and unknown resistances that add to that. I'm guessing that you know that though. If you want to win, then you win. I'd just like to again state that it is bad practice to use the neutral to ground exposed metal in anything.

 

[ajdelange]

and the ground / neutral (they are shared on the same conductor) run back to the power panel along with the two hot leads.

Ground and neutral are not shared. They are two separate conductors. As has been pointed out in other posts one (the neutral) is the 'grounded conductor'. The other (ground/earth) is the 'grounding conductor'. They are connected at the service entrance and nowhere else (in a code compliant system). A three wire outlet has one or the other of these two conductors. A NEMA 6-30 outlet will have the two phases and ground. A NEMA 10-30 outlet will have the two phases plus neutral.

 

[Malticulous]

There is a NEMA 10-30 and 10-50. They are now obsolete removed from the NEC in '96. They did (and many still do) use the neutral/ground as a current conductor for 120v parts in appliances.

 

[thargrav]

There is a NEMA 10-30 and 10-50. They are now obsolete removed from the NEC in '96. They did (and many still do) use the neutral/ground as a current conductor for 120v parts in appliances.

You are absolutely correct as of 1996 but this entire discussion is about adding the Home Depot SPA panel to an existing 3 wire 240V circuit, something this panel was designed to legally do. And once you add the SPA panel, the output is to current 4 wire code & is GFCI protected. And the existing 3 wire cable is also legal since it was installed before 1996. Now, before you fire off the "they have to be separate" statement again, I suggest you pull the cover off your post-96 main power panel. The neutral will be terminated to one buss bar and the ground will be terminated to another buss bar but the two will be electrically joined by your main power panel shell.

 

[whoaru99]

You are absolutely correct as of 1996 but this entire discussion is about adding the Home Depot SPA panel to an existing 3 wire 240V circuit, something this panel was designed to legally do. And once you add the SPA panel, the output is to current 4 wire code & is GFCI protected. And the existing 3 wire cable is also legal since it was installed before 1996. Now, before you fire off the "they have to be separate" statement again, I suggest you pull the cover off your post-96 main power panel. The neutral will be terminated to one buss bar and the ground will be terminated to another buss bar but the two will be electrically joined by your main power panel shell.

Nope. Equipment grounding wire cannot be derived from "neutral" outside the main panel. A dryer or range is grandfathered, but the spa panel is not a range or dryer, therefore the grandfathered exception does not apply to it for using the grounded (neutral) wire for equipment grounding.

Adding a GFI does not allow one to "make" equipment grounding from the grounded (neutral) wire either. If you've ever installed a GFI receptical you will note in the instruction to be compliant with NEC the receptical must be labeled "No equipment ground." if there is not a grounding wire. You cannot simply jumper the grounded wire over to the grounding screw and have compliant equipment grounding just because of a GFI.

Further, 250.114 indicates that the metal, non-current carrying parts of cord and plug connected equipment shall be grounded by means of equipment grounding wire unless excepted. Spa panels do not seem to be in the exceptions. So, it appears that the spa panel in this wiring configuration is not compliant with Code.

 

[ajdelange]

Now, before you fire off the "they have to be separate" statement again, I suggest you pull the cover off your post-96 main power panel. The neutral will be terminated to one buss bar and the ground will be terminated to another buss bar but the two will be electrically joined by your main power panel shell.

OK I did and I suggest you look at yours. Here's my picture. As you can plainly see the neutral and ground buses are not joined together. The grounded (earth) bar is in electrical contact with the panel but the neutral bar is not. As you can see there is a layer of white insulating material under the neutral bar and screws that secure the bar to the box are in insulating stand offs. Nor as you can see is there a jumper between the two. Were there a jumper or were they both bonded to the box it would violate Article 250.24(5)

"Load Side Grounding Connections. A grounding connection shall not be made to any grounded circuit conductor on the load side of the service disconnecting means except as otherwise permitted in this article."

Interestingly enough in terms of this discussion the electrician who wired this box did not, apparently, understand the code any better than you do and did jumper them. The inspector made him take the jumper out.

What you see in this picture is the two phases (large black wires), the neutral (marked, per code with white tape) and the grounding conductor (marked with green tape, again as allowed by code) each connected to its proper place in the panel.

Why is it wired this way? Because this panel is not the service entrance and the code says earth and neutral may only be joined at the service entrance. The green wire in this picture is connected to the white wire at the service disconnecting point (another circuit breaker in another box) as required. If you have a single panel in your house and its breaker is the service disconnect then you can join the neutral to the earth at that point but must not, per the article quoted above, have another interconnection anywhere on the load side of that breaker. The bond could be through the panel metal but I'm guessing that most panels are made like mine because so many houses have multiple panels now and an insulated neutral bar is required except in the box containing the service disconnect.

 

[ajdelange]

Further to my last post: After thinking about it for a bit I remembered it wasn't the panel in the picture that the electrician screwed up. It was a new panel put in at the same time as the one in the picture was rewired and what he did was exactly what you guys want to do with the spa panels. He ran the phases and neutral from the service entrance and then bonded the neutral to the ground bar in the panel. Naturally the inspector said that was a no no and the reason I probably didn't remember it is because one tends to try to suppress traumatic experiences. To bring this panel into compliance a ground wire had to be run to it from the service entrance and as the drywall was already up it had to be ripped out so they could run that wire.

 

[whoaru99]

disregard

 

[whoaru99]

YNow, before you fire off the "they have to be separate" statement again, I suggest you pull the cover off your post-96 main power panel. The neutral will be terminated to one buss bar and the ground will be terminated to another buss bar but the two will be electrically joined by your main power panel shell.

Right, the grounded wire (neutral) is bonded to/in the main panel, but the spa panel is not the main panel.

 

[ajdelange]

I'm going to be nit picky here because failure to appreciate this nit is, I believe, at the heart of this very common misunderstanding even among some licensed electricians. The neutral and the ground are bonded at the service disconnect and only at the service disconnect. If you have a single panel in your home and the mains breaker in that panel is the service disconnect then the neutral and ground busses will be interconnected in that panel. But in many cases the panel is not the service entrance and a panel breaker is not the service disconnect. In such installations the neutral and ground must not be interconnected. Disbelievers may ponder why panel neutral busses are insulated from the box whereas the ground buss isn't.

There is a very simple way to get a house with old wiring compliant and that is to run two hots and ground/earth to your equipment or panel. The ground wire then goes to the frame of any equipment, the kettles etc. All the loads must be 240V loads but one of those loads can be the primary of a 240 /120V transformer whose secondary provides any 120 needed for control, lights, buzzers etc. If the demand for 120 is small a small transformer will do. If the demand is heavy (e.g. if one wanted to run 120V elements) then the transformer would have to be large and this isn't such a hot idea.

If you have existing wiring with two hots and a neutral (white) you can easily convert this to 2 hots + ground by removing the white wire from the neutral bus at the panel, wrapping it in green tape, and connecting it to the ground bus. The other end at the outlet or subpanel must also be marked green somehow and connected to the grounding bus, contact on a plug....

You still have GFCI protection with this arrangement, it's safe (the kettles will be at ground potential) and it doesn't violate any code provisions (that I can think of).

 

[whoaru99]

The only concern I can see with that approach would be needing to change the type of plug and receptacle from (typ.) 10-30 to 6-30 to match the wiring revision..which then presents an issue for the dryer if you're trying to dual purpose the circuit.

 

[ajdelange]

To do it right you would have to change the outlet to one appropriate for H/H/G. But your clothes dryer, range or stove top is grandfathered for H/H/N. To reconnect it you'd have to change the ground wire back to a neutral. You can't have it both ways unless you install a large enough transformer to carry the whole circuit load and have a center tapped secondary. Then you would have a real 3 wire to 4 wire conversion and you could install 4- connector 120/240 receptacles and plugs on both your clothes dryer and brewing equipment. PITA though it may be clearly the thing to do if you wanted to be able to do this would be to pull 3 + ground from the panel.

 

[lschiavo]

PITA though it may be clearly the thing to do if you wanted to be able to do this would be to pull 3 + ground from the panel.

I agree. Although the receptacles are grandfathered for use with a dryer or range, I can’t see how that still applies when plugging in something other than those specific appliances.

 

[ajdelange]

AFAIK nothing is being grandfathered here. The grandfathering refers to being permitted to ground the frame of equipment to the neutral in the case of certain types of equipment. I'm not proposing that here. I am proposing converting a H/H/N cable to a H/H/G cable and terminating that in a listed receptacle for H/H/G. Lots of equipment of various types (chez moi a brewery pump, the well pump, a welder, a smoker, an air compressor) all connect that way using various types of plugs. I made the electrician put in 4-wire connections in the brewery thinking he'd be smart enough to do the same in the garage but where he could save a wire he did so I have one circuit that is H/H/G. Were I to go to an electric system I would use the 4 wire but if I wanted to use the 3 I would put the proper plug on it and proceed. If I wanted to use the circuit where the clothes dryer now pugs in I would, after the divorce, change that over to H/H/G and put in the proper receptacle. The clothes dryer would no longer be useable at that location. But rather than do that at any location with a 3 wire connection I would pull a 4 wire cable instead if possible.

Something else came to mind while thinking about this H/H/G conversion with transformer for 120V for say pumps that you wanted to connect to your control box with plugs. How would you wire those receptacles? The answer is hot to one side of your transformer secondary, neutral to the other side to the other side of your transformer secondary and ground to the G coming in to your box which should, of course, be bonded to the box and the transformer frame. The side of the transformer [Edit] secondary[/Edit] which is not connected to the outlet hot is bonded to the G wire/box. Doesn't this violate the rule about not bonding N and G anywhere at the service entrance? No it doesn't because this is a 'separately derived system'. Doing it this way is only allowed if the transformer is under 1 KVA (which it would be because you wouldn't need one larger nor would you want to pay for it).

 

[whoaru99]

AFAIK nothing is being grandfathered here. The grandfathering refers to being permitted to ground the frame of equipment to the neutral in the case of certain types of equipment. I'm not proposing that here. ...

I don't believe the implication of "grandfathered" was intended with regard to what you suggested. It was in regard to the original intended use, which was not spa panels and electric brewing systems.

 

[whoaru99]

The side of the transformer which is not connected to the outlet hot is bonded to the G wire/box.

Would you ground one end of the secondary in this case? Why not use the isolated power?