# 3 wire to 4 wire question



## Ron6519 (Mar 28, 2007)

Call in someone with electrical experience. This isn't something for someone inexperienced.
Ron


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## Andy in ATL (Aug 28, 2007)

Post in electrical. We will determine if you are smart enough. But you got to be smart enough to post in electrical, for sure.:laughing: :wink: :whistling2:


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## Stubbie (Jan 7, 2007)

> Post in electrical. We will determine if you are smart enough. But you got to be smart enough to post in electrical, for sure


???? 



Please post the electrical requirements of your new cooktop. There is a nameplate on it somewhere... give us everything on it that has to do with voltage and watts and amperage. Or give us the maker and models #. We have to make sure the wire size and breaker are correct for the cooktop.

It's a simple deal once we have this information.


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## Andy in ATL (Aug 28, 2007)

It was Introductions when I posted that, Stub.


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## Andy in ATL (Aug 28, 2007)

As Stubbie said... It's simple once we have more info.


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## macmouse (Nov 12, 2007)

I'm sorry for posting in the wrong area I'm new to this forum.
It's a Wolf 15" Induction Cooktop.

Electrical Supply Requirements 240/208 V AC, 60 Hz
20 amp dedicated circuit

The Wolf 15" (381) integrated induction
cooktop requires a separate, grounded 3-wire
240/208 V AC, 60 Hz, 20 amp service with its
own circuit breaker. It has a 4' (1.2 m) flexible
3-wire conduit for connection at the electrical
supply.


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## Stubbie (Jan 7, 2007)

Hi Mouse and welcome to the electrical forum

Thats what we needed 

Your 4 wires coming from the outlet should be red, black, white and bare or green. If not post back with what you have. I am also assuming that whatever was hooked up to the 4 wire worked correctly. 


This is what you should have









Turn off the 30 amp double pole breaker. Make sure no one is going to turn it back on while your working.

You need to verify that you have at least 12 awg copper wire on the 4 wire branch circuit you probably have 10 awg.

What you have is a 4 wire 120/240 volt branch circuit from the breaker box. The *white* wire will be unused in your case. Do not connect anything to the white wire even if the cooktop has a white wire. Just cap the white wire coming from the breaker panel off with a wire nut (just like the image shows). Now just connect red to red, black to black and then connect the remaining ground wires to each other. You may also need to connect a grounding jumper to the box if it is metal (very important). Your cooktop should have a red wire, black wire and a bare or green ground. It may have a white wire and black wire if so these are both used as hots... your cooktop does not need a neutral. If it has a white wire connect it to the red coming out of the wall box and the black to the black. The grounds as I described.
Now at the breaker box you need to change the 30 amp breaker to a 20 amp double pole breaker. And connect the same two wires that you removed from the 30 amp breaker to it. If you are not familiar or comfortable with this part hire an electrician. If you do it be sure to turn off the main breaker any breaker you remove should be in the off position before touching or disconnecting the wires. While your in the breaker box verify that the white wire going to the cooktop location is connected to the neutral bar and not the breaker.

good luck


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## elliowb (Dec 13, 2007)

Thanks Stubbie for a very detailed response to the original question. I have a similar situation and will follow your advice.

My question is from a different perspective. While my new cooktop has the 3-wire setup, the old (probably 15+ years) Jenn-air cooktop had a 4-wire connection (1 black, 1 red, 1 white and 1 bare ground). Why the difference? Especially on a brand new cooktop. I thought the new code was for added safety. Is there some minimum wattage that triggers the new 4-wire code? I've seen some cooktops with 5 burners that use the 4-wire, but many of the 4 burner cooktops have a 3-wire.

If the 4-wire is truly safer, why not add one more piece of wire to the lower wattage cooktops? It seems like even the four burner cooktops could pack a whollap if they grounded through me rather than the copper wire. Doesn't make much sense, or am I missing something? Is it that the industry is that sensitive to the cost of 30" of copper? For our sake I hope not. Thanks for your thoughts.

-- Bill


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## Stubbie (Jan 7, 2007)

Most likely the new cooktop is 240 volts only the Jenn Air was 120/240 volts and required a neutral wire. Both are grounded circuits and equally safe by todays standards.

For cooktops:

3 wires = 240 volts 2 hots and ground

4 wires = 120 and 240 volts required 2 hots, a neutral (for the 120) and ground.


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## elliowb (Dec 13, 2007)

Thanks for such a quick reply. Now it makes more sense to me. I suspect that since my cooktop has regular manually operated controls rather than something like the touch sensitive controls, it doesn't need the 120.

-- Bill


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## elliowb (Dec 13, 2007)

Hi,

I didn't have a chance to entirely uninstall my old cooktop and remove all the wiring from the box. I did today and discovered that rather than like the original poster, I only have 2 hots, and 1 white come from the panel.

However, I believe that the wiring in the entire house is run in metal conduit. Once I had the old cooktop removed, I turned the circuit back on and metered from each of the hot wires to the metal box. I got 120V on each one.

Would I be safe in attaching the ground from the new cooktop to the metal box, cap off the white from the panel, and attach the hots to the hots from the panel? Or do I need to fish a ground from the panel to the outlet? But, I don't find any grounds at all in the panel, so I'm not sure what I would attach it to. This is a house that was built in 1960, so maybe that was the standard then?

Thanks for any help you can provide.

-- Bill


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## jrclen (Feb 20, 2008)

Your metal conduit is an acceptable ground. Connect the ground from the cooktop securely to the box. Wirenut the white and connect your hot wires. You will be all set.


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## BigJimmy (Jun 30, 2006)

Andy in ATL said:


> As Stubbie said... It's simple once we have more info.


Nice to see you back, Andy! :thumbsup:


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## elliowb (Dec 13, 2007)

Thanks a lot jrclen. I've changed out switches, fixtures, and even added new circuits with no problems. Situations like this though, tell me how little I really know about electricity.

-- Bill


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## jbfan (Jul 1, 2004)

BigJimmy said:


> Nice to see you back, Andy! :thumbsup:


Jimmy, that post from andy was from nov, 07
I don't know if he is coming back. 
I hope him and Honker are ok!:yes:


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## BigJimmy (Jun 30, 2006)

jbfan said:


> Jimmy, that post from andy was from nov, 07
> I don't know if he is coming back.
> I hope him and Honker are ok!:yes:


Dang! Sorry I didn't notice. Dunno how I did that!


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## jrclen (Feb 20, 2008)

elliowb said:


> Thanks a lot jrclen. I've changed out switches, fixtures, and even added new circuits with no problems. Situations like this though, tell me how little I really know about electricity.
> 
> -- Bill


I understand Bill. I hope you are cleared up now. Any more questions just ask. We are all happy to help. Questions are much better then mistakes in electrical work. :thumbsup:


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## elliowb (Dec 13, 2007)

Hi jrclen,

Just so I have a better understanding, let me ask you one more thing if you don't mind. I've been trying to understand exactly how the electricity flows in my cooktop. In reading about the grounding conductor and a grounded neutral, I found the following on Wikipedia:

"While a neutral wire is always "grounded", it should not be confused with the electrical system's "equipment ground_ing_ conductor", which is not intended to carry any electric current during normal operation, but serves to do so in the event of a "fault", which is the unintentional imposition of current, such as during a "short circuit" or "ground fault"."

What's confusing me is if the grounding conductor (in my case the metal conduit) is not ordinarily supposed to carry any current, why doesn't my cooktop have any means to return the current. The conclusion that I'm finally coming to is that the current flows between the two hot wires (and that's what makes it 240 rather than 120) and that's why a neutral isn't necessary. And the ground still only carries current if there is a fault in the normal circuit. Is that correct?

-- Bill


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## Stubbie (Jan 7, 2007)

Hello Bill

Yep, you got it pretty well figured correctly. But lets clarify a few things first.
It's all about terminology. We have as a matter of convenience used the term 'Neutral' to describe the grounded conductor (usually white) of a 120 volt circuit. This is actually not correct, in a two wire circuit with equipment ground the white is simply a grounded leg meaning when it gets back to the service equipment it bonds with the service NEUTRAL. However it carries *all *of the return current of the branch circuit. A neutral does not. It carries the unbalanced current between *two or more* hot wires. An example would be a free standing range that has an oven and cook top burners. The nameplate on a range will state 120/240 volt appliance, meaning it needs 120 volts *and *240 volts to operate properly. So we have 2 hot wires and a grounded leg. Only the grounded leg of a range is a *neutral* which carries the unbalanced load between its 2 hot wires. A kitchen aid mixer is strictly 120 volts and therefore has a *grounded leg* that carries *all* return current of the appliance coming from *one* hot wire. 

Your cooktop is strictly 240 volts and therefore there is no grounded leg or neutral, just two hot wires and the equipment ground. No wire is brought back to the service neutral (the utility grounded conductor) and bonded to it making that wire a grounded conductor.

You are absolutely correct the current just flows in a loop as it alternates direction from the endpoints of the utility transformer winding. See the image below. Click on it to enlarge. Notice there is no connection to the grounded leg (aka neutral) on the 240 volt load. Also notice there is 240 volts potential between Leg A and Leg B with respect to each other at the transformer winding. You also see there is 120 volts of potential between Leg A and the grounded leg which is connected to the center of the transformer winding. The midpiont between legs or center of the winding is designated 0 volts with respect to earth potential.


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## elliowb (Dec 13, 2007)

Thanks a lot Stubbie. I don't know why it took me so long to come to that conclusion, but I really appreciate your confirming my thoughts and giving me more detail. The diagram makes perfect sense.

I'll definitely sleep better!

-- Bill


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## jrclen (Feb 20, 2008)

Bill, I knew Stubbie would come along with one if his great explanations and pictures.

I'd like to add 2 cents worth. Your two wires for 240 volts are opposite polarity. Picture 1 positive and 1 negative. So the electrical current flows from one to the other. Being AC power, the current reverses 60 times per second. So as Stubbie said, no neutral or grounded conductor is needed for this circuit. A voltmeter placed across those two wires will read 240 volts.

The grounding conductor, also called an equipment grounding conductor is a safety. If one of the ungrounded conductors above short circuits to ground (a ground fault), the equipment grounding conductor (your conduit) carries that current back to your electric panel and then on out to the transformer where the power comes from. That high current flow will cause a high current flow on one of the "hot" wires, which causes the circuit breaker or fuse to open and kill the power. It does this very quickly if we provide a low impedance (resistance) path for that fault current. That path can be the conduit or a grounding conductor (wire). The key point is the path going back to the source of the power, the transformer, not to the earth as many people believe.

Another type of short circuit would be for those two wires for your 240 volts to touch each other. This would be a leg to leg or bar to bar fault and again would result in very high current flow which of course would open the fuse or circuit breaker once again to protect the circuit and yourself.


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## elliowb (Dec 13, 2007)

Hi John,

Thanks for the additional information. I always like to know the 'why' of what I'm doing. What was causing me a problem in understanding the 240v circuit, was that I kept thinking that the hots had to have a return neutral and that 'somehow' the two of them together added up to 240v. I realize now that that was bad thinking because you need that total difference in potential of 240v or you need a transformer.

I guess a good analogy would be that in a regular 120v house circuit, as the current alternates, it first pushes and then pulls. While in a 240v circuit, the one leg pushes while the other leg is pulling and then they reverse roles.

Thanks again,

-- Bill


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## Kingsmurf (Feb 3, 2008)

*kingsmurf*

Stubbie . . .nice of you to help a fella

?...I didnt see where the Lad told us what COLOR his leads were? . .just
out of curiousity

? . .arent some of the newer appliance internally bonded neutral /
ground . . . .doesnt the code allow that in some circumstances?

I always like to hear the fellas tell us what color leads as
well . . .and pictures are great as well


thanks again


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## Speedy Petey (Feb 1, 2004)

Kingsmurf said:


> ? . .arent some of the newer appliance internally bonded neutral /
> ground . . . .doesnt the code allow that in some circumstances?


All new 120/240v appliances come from the factory with the neutral bonded. 
It is up to the installer to leave or remove this bond according to the type of cord they are installing. The receptacle dictates this.
All new*er* receptacles are 4-wire requiring a 4-wire cord and the neutral NOT bonded.


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