Doing a remodel job in a home and in the kitchen the old cook top had a 30a 240v
10-2 NM run to it. The new cook top has 2 power leads, 1 neutral and a ground. The new one is probably set up to run some 120v things on it, along with the 240v heat elements. Is there any way to hook this up without having to run a new 10-3 NM circuit? Otherwise the ground will end up being a current carring ground.

You are there to sell them wire aren't you?

I think you know the answer to your own question.

Well put!

We sell them the material and rent them our knowledge.

We know it is incorrect to use the EGC as the neutral, thats why they hired an electrician. They are looking for a safe, code compliant job, even though they will not be happy about the costs.



[This message has been edited by iwire (edited 04-09-2005).]

Perhaps a look at the installation instructions might shed some light on this. If it is listed for a 2 wire installation the instructions will let you know. (Although I know it is tough for us to ask for directions!)

If the neutral and the ground are tied together at the main panel feeding the cook-top. Tieing the neutral and ground (from the cook-top) together at the junction box (using exhisting ground) right below the cook-top would be the same results.
With a new circuit running 10-3, if you touch the neutral at the cook-top, it would be the same as touching the ground, since they are tied together at the main panel.
Am I wrong?

HLCbuild,
Actually I didn't see the cooktop, my help work on it. But if there is 2 hots, a neutral, and a ground, I don't see what the directions would tell you. Its pretty self explanitory.
The situation with water heaters, dryers, using the neutral is the same, kinda unclear as to why there is a difference from the main panel and the recept or junction point as far as the neutral and ground tied together.

There is no time that the NEC allows the use of an EGC as the neutral on the load side of the service disconnect.

The NEC used to let you use the neutral to ground range and dryer frames. This is not allowed anymore except in existing installations.

Current carrying conductors must be insulated, the EGC is not insulated.

One reason for the separation of the grounded and grounding conductors is to prevent a difference of potential caused by voltage drop across the conductor.

It is great you want to learn the reasons for this but you should (in my opinion) not believe you can second guess issues that have long been worked out.

If it was not a safety issue the NEC would allow it.

Bob

I can't believe this question is even being asked by an electrician.

Peter

Here's your risk:

Lets assume (theoretically) that you do indeed tie together the neutral and ground at the cooktop, connecting them both to the EGC. Now just for fun, lets sever that EGC. Customer turns on stove and causes some kind of 120 v load. Neutral and ground have been bonded at connection point. Customer touches stove. What happens? They complete the circuit. Dead customer. Your license goes bye-bye.

This doesn't happen when you keep them separated all the way back. A severed neutral is just a severed neutral. (And yes, this same risk exists in pre-1996 3-wire stoves and dryers, but that is completely besides the point).

I'm not even an electrician (which is why I barely pipe up here unless I know i'm right) but this is so blatantly obvious to me...

run a new wire and do it right

The other issue is that this is NM cable.
I don't think it was ever acceptable to use 2-wire NM on a range or dryer circuit. Pre-'96, 2-wire installations were required to be SE type cable (never was exactly sure why).
Therefore, if SE cable is encountered on a range replacement, it could be re-used.
Correct me if I'm wrong.

I have seen 2 wire Romex on dryers but that was when cars had fins. Usually when I saw Romex to a dryer it was 10-3wg. They hooked the white to the silver lug in the receptacle and used the ground on the box/backstrap. I was told it was because a (WWII) dryer/range was grounding to the neutral and the neutral had to be white. SE was the exception if the AHJ would take it.

My 1963 era house has 8-3wg Romex to the range. It is still the original 3p crow foot. I bought a cooktop that is pure 240v.

CTwireman,
I have been doing elec work for many years but do not know it all, I'm always open to learn more. Knowing the code or how to do something and knowing the theory behind it are 2 separate things.
Can you explain why touching the main panel neutral/ground bar is different than touching the junction box neutral and/or ground would be different? Other than some resistence in the wire.

jdadamo,
Your Quote:
(Lets assume (theoretically) that you do indeed tie together the neutral and ground at the cooktop, connecting them both to the EGC. Now just for fun, lets sever that EGC. Customer turns on stove and causes some kind of 120 v load. Neutral and ground have been bonded at connection point. Customer touches stove. What happens? They complete the circuit. Dead customer. Your license goes bye-bye.)

Why would that complete the circuit? It is already completed back at the panel. And unless the neutral gets disconnected at the panel from the cook top, electricity will of course takes the easier path, not through the customer.

I know the correct way is to run the 10-3, and in some cases probably good reasons for it. That is what I will do, but it does raise some good theory questions.

aldav53, I clearly said in my post "now for fun, let's sever the EGC." So, in that case, no, it is not connected back to the panel. It's sitting there broken. It's a hypothetical situation that I was using to explain to you why it is NOT equivilant to take that approach, because you asked if it was.

aldav53,

I'd strongly suggest getting a copy of Soares 'Grounding'. This is the _classic_ textbook on why we ground and why we ground in the way that we do. 'Grounding' is not easy, and the historical section will make it clear that grounding is not without controversy. In fact, at one point some of the early electrical safety organizations _prohibited_ grounding of electrical systems. (Check out the historical appendix of the book.)

Alas, the original author (Soares) is dead, and the book keeps being revised to match the current NEC, which means that it now reads as though it were written by committee (the same concepts repeated several times in ways that IMHO don't reinforce useful knowledge, having several examples in a row that look at different aspects of something, but using _different_ base examples when IMHO it would make more sense to look at the _same_ system form different viewpoints, etc.) But the text still covers the essential material, and is worth reading for this reason alone.

You don't need to consider jdadamo's failure condition to understand why the shared neutral for the cooktop is not desirable. The real problem is pointed to in your statement:

You also said

These are two common (and dangerous) misconceptions.

The first thing to understand is that electricity does _not_ simply 'take the easiest path to ground', or even the 'easiest path' in general. Electricity takes _all_ paths back to the _source_ of the current, in proportion to the ease of the path. If you arrange a system where the electricity has two paths back to the source, one through a thick copper wire, and one through a person, then _most_ of the electricity will follow the wire, and a small bit will go through the person. Make the difference in resistance large enough, and the current flowing through the person will not even be noticed.

Because electricity will take _all_ available paths, the grounding done in premises wiring systems is known as 'single point grounding'. All metal that _should_ be at ground potential is 'bonded' using equipment ground conductors and grounding electrode conductors. This makes sure that during normal operation all of this metal is at the same voltage, so that there isn't a shock risk. Then this entire 'grounded' system is connected to the neutral of the electrical supply at one, and only one, location. Because there is only a single point of connection, there is no closed path that the electricity can follow, and thus current does not normally flow in the ground system. That latter point is the crux of the issue.

The neutral is the 'grounded conductor'. It is insulated and _expected_ to carry current. The grounding system, on the other hand, includes essentially all other metal, and may or may not be insulated, but is _not_ expected to be carrying current. When you make _two_ connections between the neutral system and the grounding system, you change the story: now there are closed circuits in the grounding system, and current _will_ flow in the grounding system.

Now, if the metal frame of the range were bonded to the neutral conductor, rather than to an equipment grounding conductor with an isolated neutral, but the range itself were completely insulated from everything else, than I would agree, this would be exactly the same as the 'proper' connection back at the panel. But if the frame of the range has _any_ metallic contact with any other grounded metal, then the net result would be multipoint grounding and the introduction of current into the grounding system. If this current were flowing, for example, in the water pipes, then even without any sort of fault condition or failed conductor, you could have a shock hazard.

As iwire noted, previous versions of the NEC permitted the use of the _insulated_ neutral conductor to bond the frame of things like ranges, presumably because the total imbalance current of this load would be pretty small, and thus the amount of current potentially placed on the grounding system would be _very_ small. But it is interesting to note that this sort of shared neutral/ground was only permitted if the feed went back to the _main_ panel. If the feed went back to a subpanel, then the feed to the range had to be a four wire feed.

I'd also like to call attention to a situation where multi-point grounding is commonly seen, even though it is undesirable. In urban settings, it is quite common to see several houses, possibly an entire block, fed by a single transformer. Each house has their own ground to neutral bond in their main panel, and the city water supply pipe is used as one of the grounding electrodes. The city water pipe is a metallic system that connects several homes, and is clearly a 'parallel path' for neutral currents. In some cases, the neutral in the electrical system can fail, but the entire electrical system appears to function normally, since the neutral current is flowing through the pipes to an adjacent house, and then through the ground bond in that other house. Plumbers have been killed working on the plumbing pips because they've interrupted the neutral current, and experienced plumbers place jumper cables across sections of pipe that they are cutting apart. The next time you are in a home that has metal water pipes coming in from the street and a shared transformer, put a clamp meter around the pipe or the grounding electrode conductor to see what sort of problems multipoint grounding can cause.

-Jon

[This message has been edited by winnie (edited 04-10-2005).]

winnie,
Very good explanation. The only part that I might question some is if a person touches the cooktop, the resistence is going to be so much higher than the wire path, they wouldn't get shocked. But of course we don't want to take any chances at all, and should wire it with no chance of a path. The point about making a connection at one point only, makes great sense.
Again, very good..
Thanks,

What are the chances someone might touch the sink and the cooktop? Or the cooktop, and a grounded appliance? Or someone else touching one of those items? That parrelel path to ground from the current carrying surface of the cooktop posses a hazard.

Let me tell you of a service call horror story: I got a after-hours call from a resturaunt, where the dishwashers had reffused to work, and the manager only called to appease them.... I was about to leave when he told me that. Then tells me why - He said the dishwashers "claimed to be getting shocked from the sink." So I went back and finangled my best spanglish with the guy mopping the floor, who pointed to the sink and a metal counter. Then to the sink and another metal counter. 180 from one to the sink, 120 from the other, 240 to both. The garbage disposal was using the plumbing as a neutral, and the counters were installed with 3" screws that penetrated different circuits on each hot metal wall. I told the manager who didn't beleive me either, and refused to have me fix it. I asked one of the dishwashers how long it had been going on, he said years! (I called the boss who had me pull the breakers, and sharpie the hazard on the panel before I left. We called the city in the morning.)

So imagine this cooktop, and its "ground fault", any time your customer touches an appliance, or the sink, getting more than 5 milli-volts across their heart.

Let me tell you something very disturbing.

A few weeks ago I changed employers. He sends me to a customer's house and tells me the receptacle for their gas range isn't working. Ok..so I plug my tester in and it says open neutral. So I cap the problem wire and re-feed the recaptacle. I'm in there for about 20 minutes. Later I see my boss at another job. He says I should have just used the EG for the neutral.(He uses more "colorful" language) I was like....huh? are you serious...?joke right? ..He says: We shouldn't even be the ones to fix it. That's the modular company's problem..they should be the ones to come fix it...who's gonna pay your salary to fix it...and so on and so fourth.

I'm like....I have never done that in my life...and i will never do that in my life..

I can't believe it. I have to get out of there. the crazy part is that the reason the house was built was because the other one burned down. I can't believe it. Can you?...keep in mind this is a guy who's been around.(ex union...supposedly).he's in his 60's. his son has been doing electrical work for (supposedly) 10 years and has no license.

crazy. just crazy.

on a funny note. his son was acting "the man" one day in front of the cabinet guys. he pulled me over and says:"see right here."...
pointing to the countertop receptacles....
"see right here...technically you should have another outlet here..."
I go:"Article 210.52 C2 reads:....measured horizontally...blah blah blah ect"
he tries to cover his ass:"the ispector this the inspector that"
I go:"he doesn't know how to read...blah blah blah."

I can't believe it. Nothing shocks me anymore(no pun intended)

[This message has been edited by Clydesdale (edited 04-21-2005).]

[This message has been edited by Clydesdale (edited 04-21-2005).]

when i try to edit my post, i encounter HTML in my post...pretty annoying.

Some cooktops have no metal just all glass top, non conductive, but still a good idea to run the neutral.

Something related but sort of opposite -
Though we are a commercial/industrial contractor I have seen (in years past) many of the following. Older houses that were wired with old cambric coated romex that was a two wire cable, no grounding conductor. Many of the older journeymen I worked with (I was a helper) would jump the neutral to the ground allowing a standard grounding receptacle to be installed where there were only 2 wires. Must have worked because I don't recall there ever being any problems or callbacks. (or fires either) I have not seen or done and residential work in 25 years but I do remember that! Has anyone see this before?

Welcome to the forum lear

There are a few problems with using the neutral as the EGC.

The first one that comes to mind is that if the neutral becomes broken any grounded appliance on that circuit will end up with an energized enclosure.

Lear, I have seen that "bootleg" ground many times, usually done to "fool" the inspectors plug in tester.
Biggest danger of this was illustrated in a situation I found a few years back. Someone had jumped the neutral to ground on a receptacle. Someone else had tapped the circuit upstream but had reversed the hot and neutral when putting things back together. End result was a hot ground! Very scary!

Thanks iwire - Looks like a great board!
Isn't it odd that it ""fooled" the inspector every time? I remember the inspectors showing up, shooting the breeze with the boss and signing the permit after checking the work. In hindsight, I can't help but think the inspectors must have known that this was going on. Being green I just though this is the way it was done. When I was the 4th yr helper I would tell the green guys; "this is the way we do it." I'm guessing there are 1000's of older houses around the country where this was done.
Bill

[This message has been edited by LearJet9 (edited 04-27-2005).]

[This message has been edited by LearJet9 (edited 04-27-2005).]

Those little three light plug in testers are _quite_ limited.

They simply measure voltage between the three pins of a standard receptacle. If you have voltage from the 'hot' pin to the 'neutral' pin, and voltage from the 'hot' pin to the 'ground' pin, then they light up 'correctly wired'. A bootleg ground would give exactly the same indication. In fact, if hot and ground were reversed and you had a bootleg ground, you would get the exact same 'correctly wired' reading, in a _very_ dangerous situation.

There are testers that can detect a bootleg ground; they are much more expensive. For example: http://www.mytoolstore.com/ideal/ide05-05.html

-Jon

How about we do it right because we know the code and know the risks involved if we take shortcuts. The EGC is strictly for ground fault currents. The neutral is an intentionally grounded conductor used to carry inbalance and return voltage safely to ground. Do it right the first time and sleep well at night.