Our house was built in 2003 and it came with a GE 24" microwave oven that uses 120 volts/20 Amp. The microwave stops working so we went out and bought a KitchenAid convection microwave oven that requires 20 Amp, 240 volts, 60 Hertz.

The old microwave oven uses 12/2 w/g romex from a subpanel. In order to use 240 volts, I understand that I'd need to install 2-pole 20 amp breaker, and probably my best bet is to run a new 12/3 w/g romex. Use the black and red wires for hot, white for neutral, and bare wire for ground.

The problem is that it's a two-story house and it's nearly impossible for me to run a new line without ripping out some drywalls which I'm trying to avoid if possible. The house sits on a concrete foundation and the joists on the first floor's ceiling are running vertically from oven to subpanel. I've been on the attic but saw no signs of hope.

The question I have for you is: Can I use the existing 12/2 w/b romex? I'm thinking about using the black and white wires for hot and tape both ends of the white wire with red tape. Use the bare wire as neutral and tape both of its ends with white tape. Finally, share the ground with bare ground wire of the built-in oven sitting below. Just above the microwave oven, there is a built-in oven running 240v/30Amp/60Hz on a 10/3 w/g from a main panel.

So, the wiring would be:

MICROWAVE OVEN SIDE 12/2 w/g SIDE
Red wire <---------> white wire taped red
Black wire <---------> black wire
White wire <---------> bare wire taped white
Bare wire <---------> bare wire from built-in oven (10/3 w/g)

Thanks in advance for any help.

--
Quang

Is it okay to use bare wire as neutral?Absolutely 1000% NO!


Lets get the facts.
Is this new oven 240v or 120/240v?
Meaning does it even require a neutral? A straight 240v load does NOT require a neutral and you CAN use your 12/2 to power it.

Does it have a plug? What does it look like or say on it?

Like above, you may not need a Neutral, Reidentify the white as hot at both ends, Green or bare for ground. The ground must run with the supply. If you have a Neutral on micro,
You will need new wiring. The plug will tell all.

Like above, you may not need a Neutral, Reidentify the white as hot at both ends, Green or bare for ground. The ground must run with the supply. If you have a Neutral on micro,
You will need new wiring. The plug will tell all.

Thank you both stanfortyman and stratmando for quick responses. Here's the exact text from the electrical section of the product's specifications:

20 Ampere, 240 Volts, 60 Hertz (1/second). AC-ONLY. USE COPPER WIRE ONLY. A FOUR-WIRE OR THREE-WIRE, SINGLE PHASE ELECTRICAL SUPPLY REQUIRED. A TIME-DELAY FUSE OR CIRCUIT BREAKER AND SEPARATE CIRCUIT IS RECOMMENDED.

The product is listed here: KitchenAid®: Microwave Ovens (http://www.kitchenaid.com/catalog/product.jsp?src=Microwave+Ovens&cat=137&prod=1353)

If you clicked Installation Guide PDF link on the bottom of the page the 3-Wire cable installtion shows both white and bare wires from the unit are wired together.

So I wire them up as followed?

FROM MICROWAVE: FROM POWER BOX:
Black <----> Black
Red <----> White (taped red)
White + Bare <----> Bare

Thanks,
Quang

I would say wire like your last post. New construction and remodel require 4 wires(seperate neutral and ground.
If I couldn't get extra wire there, I would do 3 wire.

In AC circuits, the voltage on the black wire carries power to the appliance and the white wire is the intended return path to ground. If the appliance you're powering has a metal chassis, it'll usually have a third wire (the bare copper wire) connected directly to the chassis. That way, if the conductor in the black wire accidentally shorts to the chassis, the bare copper wire will carry the current and (hopefully) allow the circuit breaker to trip before you're electrocuted.

Because of this design, it can be dangerous to use a "cheater plug" to allow you to plug a three-wire cord into a socket with only two contacts. (In this case, the safety ground is missing, and you're putting yourself at risk of electrocution.)

Quang,

Do Not Wire you Outlet as Directed above!You will be putting 120 VAC directly to ground and you can kiss the new oven good bye.

First: Why do you sat your house is a three wire supply?

Second, If the Convection Oven will draw no more then 20 Amp, then yes you can use the existing wire, however, because the vendor is asking you to use slo-blow breakers, my immediate concerns are that the oven will draw more than the given 20 Amps. Look at the label on the back of the oven, does it give a Mim and Max Amperage. If it does, use the max amperage and the wire for that amperage along with the proper out let.

Third; Two wire can be used to do what you want. First you need a 20 amp single throw dual pole circuit breaker. Next, the breakers need to be close the Black lead in the box. That will mean that you will have to move a CB. If you don't have 2 empty slots together.

You place the black wire on the first breaker. Place the White wire on the second breaker. Wrap a small amount of Black or Red tape on the whits wire to flag that this wire is not a return wire. Next, the bare wire has to go over to the Neutral bus bar. At the receptacle end, Black would go to Black, White, with tape on it would go to the second power pole, It might show "white" on the receptacle or red. The bare wire must go to neutra connectionl.

The oven's should be grounded to it's own frame.

If you feel the least bit queasy about working around the main utility, it means you are smart. Call a licensed electrician and have him pull the required permit. When the work is finished, the work will be inspected. Keep the inspection certificate,

Just so you know, even if you disconnect the main breaker to the house, there is still electricity on the main lugs. More than enough to turn you into a bowl of soup, should you hit the wrong wires?

In AC circuits, the voltage on the black wire carries power to the appliance and the white wire is the intended return path to ground.I don't mean to sound rude bit this is VERY incorrect.

A) The white is not always the "return" wire. Sometimes it IS a hot, or ungrounded, conductor, and acts just like a black or red for instance.

B) The white, or neutral, is NOT a return path to ground. This is a LONG perpetuated MYTH. Voltage is NOT seeking ground, it is seeking it's source.

The product is listed here: KitchenAid®: Microwave Ovens (http://www.kitchenaid.com/catalog/product.jsp?src=Microwave+Ovens&cat=137&prod=1353)According to the installation instructions that unit IS a 120/240v feed. The cable you have IS NOT appropriate. You DO need two hots, a neutral AND ground.

You can use 12/3wg NM cable. DO NOT use the 12/2.

Stan,

Okay, I see you are a licensed Electrical Contractor, dose that also carry with it a Master's or Journeyman's electrical licence? That's a real question, by the way. In Virginia, I can become an Electrical contractor but that would not allow me to pull permits. Only licensed Electricians can do that.

I fully understand that if the owner switches to 12/3 then he would have and over wrapped cable containing Black, Red, White and Bare.

But to do that, the poster will have to run a new cable from the SEP panel upstairs to the kitchen. He does not want to do that.

Regardless, He will need to change the breaker out, in favor of SPDT 240 20 amp, correct. Also, the existing 12/2 cable can be used by using the black and white (wrapped in black or red tape at both ends) to handle the two 120 legs of power and bare would then connect to the Neutral at the SEP panel?

Espically since it is 20 amp rated conductors. Am I still within code guide lines?

Next, why change out the conductors if what is already there can safely be used to carry the required power to the needed load?

Also, I read the Installation instructions and they list 20 amp max, but ask for slow-blow fuse or citcuit breakers at both ends. I've never heard of installing two breakers for one circuit, is that allowed by code and where would you put the breaker at the load end?

Okay, I see you are a licensed Electrical Contractor, dose that also carry with it a Master's or Journeyman's electrical licence? That's a real question, by the way. I'm not sure why this is even important.
In my state there is NO statewide license. If a locale requires a license you must acquire that license. Some areas do reciprocate though.





I fully understand that if the owner switches to 12/3 then he would have and over wrapped cable containing Black, Red, White and Bare.

But to do that, the poster will have to run a new cable from the SEP panel upstairs to the kitchen. He does not want to do that.He does NOT have a choice.




Regardless, He will need to change the breaker out, in favor of SPDT 240 20 amp, correct. Also, the existing 12/2 cable can be used by using the black and white (wrapped in black or red tape at both ends) to handle the two 120 legs of power and bare would then connect to the Neutral at the SEP panel?NO. This is NOT equal to two 120v legs. It is simply a 240v circuit.
Even though each leg is 120v to ground, there is NO neutral to give you 120v, so the 120v is irrelevant.
This will require a 2-pole 20 amp breaker. Breakers are not rated in SPST or DPST terms. There are single pole, 2-pole and 3-pole breakers. They are ALL single throw.




Next, why change out the conductors if what is already there can safely be used to carry the required power to the needed load?Again, because there is no neutral present in the existing cable if the cable is used for 240v.
A 12/2 cable can be used for 120v or 240v but NOT both at the same time.
He needs a 120/240v circuit because there are BOTH 120v and 240v loads in the same appliance.




Also, I read the Installation instructions and they list 20 amp max, but ask for slow-blow fuse or citcuit breakers at both ends. I've never heard of installing two breakers for one circuit, is that allowed by code and where would you put the breaker at the load end?I did not notice that in the instructions. I have no idea how they would require a breaker at the load end or where it would be placed.

According to the installation instructions that unit IS a 120/240v feed. The cable you have IS NOT appropriate. You DO need two hots, a neutral AND ground.

You can use 12/3wg NM cable. DO NOT use the 12/2.

Actually, the instructions are for 27" and 30" microwave ovens. I think the 120v is referred to the 27" model and 240v is for the 30" model. If you looked at the top/left of page 5 where it describes on how to use 3-wire connection, it seems that I can use 12/2 w/g NM cable.

Quang,
First: Why do you sat your house is a three wire supply?

Second, If the Convection Oven will draw no more then 20 Amp, then yes you can use the existing wire, however, because the vendor is asking you to use slo-blow breakers, my immediate concerns are that the oven will draw more than the given 20 Amps. Look at the label on the back of the oven, does it give a Mim and Max Amperage. If it does, use the max amperage and the wire for that amperage along with the proper out let.


There is a Convection Oven right below the Convection Microwave Oven that I'm struggling with wiring. The Convection Oven uses 30 Amp 10/3 w/g.



Third; Two wire can be used to do what you want. First you need a 20 amp single throw dual pole circuit breaker. Next, the breakers need to be close the Black lead in the box. That will mean that you will have to move a CB. If you don't have 2 empty slots together.


I need to arrange breakers with two new ones since I ran out of room. Basically, I need a [20,20/20,20] and [15,20] breakers. 20/20 means dual pole.



You place the black wire on the first breaker. Place the White wire on the second breaker. Wrap a small amount of Black or Red tape on the whits wire to flag that this wire is not a return wire. Next, the bare wire has to go over to the Neutral bus bar. At the receptacle end, Black would go to Black, White, with tape on it would go to the second power pole, It might show "white" on the receptacle or red. The bare wire must go to neutra connectionl.

The oven's should be grounded to it's own frame.


I understand this part.



If you feel the least bit queasy about working around the main utility, it means you are smart. Call a licensed electrician and have him pull the required permit. When the work is finished, the work will be inspected. Keep the inspection certificate,

Just so you know, even if you disconnect the main breaker to the house, there is still electricity on the main lugs. More than enough to turn you into a bowl of soup, should you hit the wrong wires?


Good suggestions.

Thanks,
Quang

Could someone please take a moment and read page 5 of the installation instructions (found here: KitchenAid&#174;: Microwave Ovens (http://www.kitchenaid.com/catalog/product.jsp?src=Microwave+Ovens&cat=137&prod=1353))

And see if I can install this microwave oven using the existing 12/2 wg NM cable. I understand that I need to install a dual-pole single throw 20 Amp breaker. I just want to find out whether I can get away with the existing 12/2 gw NM cable or I need take out a hammer and start making holes on drywalls which I'm trying to avoid doing.

Thank you very much for your help in advance.

Quang

Look at the "3-wire" instructions. It states:
2. Connect the 2 white wires (D) and the green (or bare) ground
wire (of the microwave oven cable) using a UL listed wire
connector.

This is for an EXISTING older "3-wire" 120/240v circuit. Such as for a range. YOU DO NOT have this type of circuit.

You DO need 12/3.

NEITHER of these ovens is straight 120v. This is right on page 2 of the instructions:

When a 4-wire or 3-wire, single phase 120/208 or 120/240
volt, 60 Hz, AC only electrical supply is available, a 20-amp
maximum circuit protection is required, fused on both sides
of the line.


I see now about the "both sides" comment. This does not mean both ends of the circuit. It simply means both legs of the circuit. This just means a two-pole breaker.

... Also, the existing 12/2 cable can be used by using the black and white (wrapped in black or red tape at both ends) to handle the two 120 legs of power and bare would then connect to the Neutral at the SEP panel? ...

NO, NO, NO! The bare or green wire can never be used as a current carrying conductor. The neutral (white) wire is carrying as much current as the black wire in a 120v circuit or, in this application, as much current as the difference between the black and red wires. The safety ground is connected to the chassis of the appliance to clear a fault (blow the breaker) when it occurs. If you think about it, if you use the ground as a neutral, if it gets lifted or broken somewhere down the chain of outlets or in the panel, that appliance chassis/case/bare metal can become hot and be a shock hazard.

Stanforty,

The question about the difference between a Contractor's License and Master Electrician's license was for my education only because I do not know what the difference(s) if there are any, not to cause angst.

The OP has stated that his home is a three wire drop. Which means two hots and ground or neutral. Correct? We all know that White is not always used as Neutral, just look at any switch loop, correct so far?

If Black and White are used to carry the voltage to the appliance outlet, they will deliver 240 VAC to the receptacle. All so, we know that you cannot take a 120 tap off the circuit from the breaker to the appliance. The only place the tap can be placed is inside the appliance itself, which is a common arrangement, correct?

All I am saying is that there really is no need to change the conductors unless the amperage is requires a change.

Black on one breaker, White (wrapped with Red tape) on both the breaker and the receptacle. Bare ground serves as the Neutral return. This is an "Grandfathered" acceptable circuit on a three wire serve drop.

Mr. Miller, I have never said to put power to the ground or bare wire. If you go backwards on my first entry I specifically pointed out the error.

Look at the "3-wire" instructions. It states:
2. Connect the 2 white wires (D) and the green (or bare) ground
wire (of the microwave oven cable) using a UL listed wire
connector.

This is for an EXISTING older "3-wire" 120/240v circuit. Such as for a range. YOU DO NOT have this type of circuit.

You DO need 12/3.

NEITHER of these ovens is straight 120v. This is right on page 2 of the instructions:

When a 4-wire or 3-wire, single phase 120/208 or 120/240
volt, 60 Hz, AC only electrical supply is available, a 20-amp
maximum circuit protection is required, fused on both sides
of the line.


I see now about the "both sides" comment. This does not mean both ends of the circuit. It simply means both legs of the circuit. This just means a two-pole breaker.

In the previous post, I made a mistake; I meant to say 12/2 wg. I edited and I think you knew I meant to say 12/2 wg and not 12/3 wg.

The part I don't understand about the 3-wire connection where the neutral wire and green (or bare) are twisted as mentioned in the product's instructions is that it sounds dangerous. I suppose the ground is connected to the cover of the oven. So with this connection, wouldn't it shock me if I touch the cover?

Before I go any further with this question, please tell me what wires you have coming from the breaker to the receptacle. Are they Black, Red, White and bare or are they Black, White and bare ground?

Also, I'm going to pull my code book (2008) and make sure that my suggested connection method will allow for Black to Black, White with Red Tape to the Red wire, their white and bare connection to your Bare which is connected to the Neutral bus bar, not the ground bus bar inside the SEP panel.

If I'm out of step from the rest of the electrical world I'll let you know.

Please let me know how many wires are coming from your wall. Personally, I do not understand their tying White (Neutral) to ground. Neutral and ground serve two different purposes until they get to the Service Disconnect Panel.

Gentlemen electricians, regarding using a bare conductor as the neutral and equipment ground, for "counter mounted cooking units", as quoted in the NEC, please refer to the Exception for Section 250.140 Frames of Ranges and Dryers, (Both 2005 and 2008 editions).

For a home with an existing 2 wire cable with ground, the bare is allowed to be used as the neutral and equipment ground per this exception.

Since this is a counter cooking unit, and it has an existing 3 wire cable, (2 wire with ground), I see no issue with connecting it as per the 3 wire system shown in the instructions.

For a home with an existing 2 wire cable with ground, the bare is allowed to be used as the neutral and equipment ground per this exception.This is ONLY allowable if the existing cable is type SE. The bare wire in NM cable is not, and NEVER was, allowed to carry regular circuit current. PERIOD.
Frankly I am surprised that anyone is even suggesting it can.

Here is the applicable code section:

250.140 Frames of Ranges and Clothes Dryers

Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be grounded in the manner specified by 250.134 or 250.138.

Exception: For existing branch circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be grounded to the grounded circuit conductor if all the following conditions are met.

(1) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.

(2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.

(3) The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.

(4) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.



See, the exception is that the grounded conductor could also be used as the grounding conductor. NOT the other way around.
A NEUTRAL WAS ALWAYS REQUIRED!

Standforty man,

Well I'm in serious trouble, because my place has a three wire drop and three wires com into the SEP. Two are Hot and one goes to the Neutral bus. On the neutral bus, both ground and neutrals are connected. Physically, there is no grounding bus in the SEP.

So I have only two hots and a Neutral, The house is currently receiving a 200 amp service. Now I know the at the SD panel, ground and neutral meet up. So I understand the wisdom of using the neutral bus for both ground and neutral connections. What I don't understand is how two electricians can read the same code cite and come up with two different answers both supported by the same text in the book. Sorry, that makes no sense to me.

Is there a method in place to get the NEC to explain what the paragraph is actually saying>

Sorry Don. I am not following you.
How does this apply to the topic at hand? Meaning a household cooking appliance.

Is there a method in place to get the NEC to explain what the paragraph is actually saying>
The NEC Handbook is a BIG help in this respect.

Excellent, someone reads the exceptions to the exception.

Now the poster has a very clear answer.

Nicely done, Stan.

Before I go any further with this question, please tell me what wires you have coming from the breaker to the receptacle. Are they Black, Red, White and bare or are they Black, White and bare ground?

Currently, it's a 12/2 wg (3-wires: black, white, and bare) NM cable. It's hooked up to a standard white 3-leg receptacle like the ones around the house. The old 24" microwave has a standard 3-leg plug like the one from a carpet vacuum. Had my wife wanted a 24" or 27" microwave there wouldn't be a problem. Hey, but I don't blame her; she wants something to match with the rest of other appliances.

I was aware of the voltage difference, but I was told it's going to be an easy job. :confused:

This is ONLY allowable if the existing cable is type SE. The bare wire in NM cable is not, and NEVER was, allowed to carry regular circuit current. PERIOD.
Frankly I am surprised that anyone is even suggesting it can.

Here is the applicable code section:

250.140 Frames of Ranges and Clothes Dryers

Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be grounded in the manner specified by 250.134 or 250.138.

Exception: For existing branch circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be grounded to the grounded circuit conductor if all the following conditions are met.

(1) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.

(2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.

(3) The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.

(4) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.



See, the exception is that the grounded conductor could also be used as the grounding conductor. NOT the other way around.
A NEUTRAL WAS ALWAYS REQUIRED!

:confused: I'm totally confused now! :confused:

First, there was hope, then little hope, then some hope, and it now looks like I'm going to have to bring out the hammer and knock down some walls. :o I've been staring at the walls and scratching my head. :confused:

:confused: I'm totally confused now! :confused:
Really? I had hoped it was very clear.
What are you unsure about?

Really? I had hoped it was very clear.
What are you unsure about?

I didn't mean to say that your posts were not clear. I think they are very helpful and make a lot of sense. It's me who lacks of knowledge about electrical wiring. After reading posts from various people I'm confused as to whether I will end up tearing down the walls, sale the unit and buy something else, or hire an electrician to do the work. I'm an average DIYer and I like to do it myself if it's feasible.

We spent some $1500 on this unit and hate to sale it at a loss. I'm afraid Sears might not want to take it back since we have it for a month now. Anyway, we rather keep this unit.

I really appreciate your and others' help.

Please keep talking. Maybe there is still a better answer out there.

Well for one thing, Sears has a 30 day, free return policy. That solves the problem for you one way.

However, why are you thinking that you need to knock walls down? When I had to change the conductors from 10/3 to 8/3 for a new range/oven @ 40 amp, all I had to do was get my hand inside the wall and pull the two staples out, then I attached a "Chinese finger" onto the end of the 10/3 and used the existing 8/3 to pull the new wire down to the SEP.

Now I only had to pull about 20' of cable, so it went quite smoothly. However if you are the least bit unsure of what you have to do in the SEP, then under no circumstances should you attempt to do the work. You can do all the prep work, for example pulling the cable, than call the electrician to do the connections and test the work,

Regardless, though of who does the work, someone will have to get an electrical permit. Home owners can get permits, however, If I'm hiring someone to do the work for me, I would want him to do the entire job which would include pulling the new conductors and getting both the permit and the required electrical inspection.

Hook up the Black to breaker, Identify white as red or black, connect to Breaker, Neutral and ground to ground. You should already be cooking. Don't let it all get confusing. Use the Metal plate with Greenfield connector, and call it a day.

"Sorry Don. I am not following you.
How does this apply to the topic at hand? Meaning a household cooking appliance."

Okay, I only have three populated lugs on my SEP. They are two hots and one Neutral. The Neutral Bus Bar is populated by both Bare and White wires.


There is no way for me to attach a bare wire to Ground, because there is not a physical Ground bus bar. If I were to replace the conductors with a 12/3 line to the oven's receptacle, I would have to attach both the White and the Bare wire to the Neutral bus, correct?


With respect to the existing 12/2 conductors, what difference does it make whether I use White or Bare for ground, they are both connected at the same connection point. While White can carry current, (as in a 120/20 amp switch loop circuit) what stops ground from doing the same? Ground will have to carry short circuit current safely to a ground rod and isn't a short circuit capable of a very large amperage rate even if for a very short, no pun intended, duration? Is your thinking directed at the size of the 12/2 Bare wire? Because the bare wire is insulated within the cable sheathing, is it not?


Why this in important to me, because I'm playing catch-up with re-learning the NEC code and implementing the current code to update some horrible electrical work that was a gift from a previous owner. I'm working very hard at learning. I haven't had to study basic electricity since 1972. From then on it was all electronic work both in the field and in labs.

If I've got something wrong because I remembered incorrectly then I've got two problems. One the work I did was incorrect and has to be done properly and two, the electrical inspector that approved what I did, needs to be re-educated.

Hook up the Black to breaker, Identify white as red or black, connect to Breaker, Neutral and ground to ground. You should already be cooking. Don't let it all get confusing. Use the Metal plate with Greenfield connector, and call it a day.

Somehow I feel this is going to work, but this is what others suggested not to do. :o

Anyhow, before doing anything, I'm going to call in a licensed electrician, have him explain what's involved. I go get a permit, then have him do the wiring. I'm familiar with the permit process as I have done my garage to game room conversion last year.

Worst case, I can see that by cutting four 5"x5" holes on the ceiling I should be able to run a new 10/3 gw cable from microwave to the subpanel sitting under the stairway. The distance is about 20 feet. I installed some recessed lights before on the same ceiling so I'm familiar with running cables across the joists.

Somehow I feel this is going to work, but this is what others suggested not to do. :o

Anyhow, before doing anything, I'm going to call in a licensed electrician, have him explain what's involved. I go get a permit, then have him do the wiring. I'm familiar with the permit process as I have done my garage to game room conversion last year.

Worst case, I can see that by cutting four 5"x5" holes on the ceiling I should be able to run a new 10/3 gw cable from microwave to the subpanel sitting under the stairway. The distance is about 20 feet. I installed some recessed lights before on the same ceiling so I'm familiar with running cables across the joists.

Quang,

Do not get the permit yourself! If you are calling in an electrician to do the work, let him submit the required plan and obtain the permit. If you get the permit yourself, then you are going to be held responsible for any mistakes the electrician made during the inspection, not the electrician.

If the electrician pulls the permit, then he is responsible to repair any mistakes he made, not you.

That's the way it works here in Virginia. Only a home owner or a Master electrician can pull permits with the appropriate forms and a drawing of the proposed work.

Quang,

Do not get the permit yourself! If you are calling in an electrician to do the work, let him submit the required plan and obtain the permit. If you get the permit yourself, then you are going to be held responsible for any mistakes the electrician made during the inspection, not the electrician.

If the electrician pulls the permit, then he is responsible to repair any mistakes he made, not you.

That's the way it works here in Virginia. Only a home owner or a Master electrician can pull permits with the appropriate forms and a drawing of the proposed work.

Good suggestion. I will keep that in mind.

I do appreciate your and others' help. This is a wonderful forum.

Stanforty,

Light bulb on, 2X4 across the top of my head! By Jove I think I now understand your issue with the cable.

I re-read your previous posts and just now picked up on why neutral is needed.

It is because the appliance needs both 120 and 240VAC correct? Therefore I also need to supply a Neutral and a ground.

But I have no way of supplying a ground because I have only three wires on the Service Drop. Two Hot, 1 Neutral. My only choice, if I follow your instructions correctly, is to wire both Neutral and Ground to my Neutral Bus bar.

Why the commotion if I do it as I originally suggested? The only difference would be the bare wire serving a neutral as to the installation, the nm cable does shield the bare wire.

These are questions, I'm hung up on the understanding why, since in both cases you would be getting 120/240 to the receptacle. Which by the way, I haven't found an outlet rated at 120/240 20 amp. Do they even make them or would Mr. Quang have to use a 30 amp outlet which would force him to rewire with 10/3 AWG and a 30 amp breaker.

Believe me I'm not trying to be a pest, I am trying to understand your logic over mine.

Stanforty,

Light bulb on, 2X4 across the top of my head! By Jove I think I now understand your issue with the cable.

I re-read your previous posts and just now picked up on why neutral is needed.

It is because the appliance needs both 120 and 240VAC correct? Therefore I also need to supply a Neutral and a ground.

But I have no way of supplying a ground because I have only three wires on the Service Drop. Two Hot, 1 Neutral. My only choice, if I follow your instructions correctly, is to wire both Neutral and Ground to my Neutral Bus bar.

Why the commotion if I do it as I originally suggested? The only difference would be the bare wire serving a neutral as to the installation, the nm cable does shield the bare wire.

These are questions, I'm hung up on the understanding why, since in both cases you would be getting 120/240 to the receptacle. Which by the way, I haven't found an outlet rated at 120/240 20 amp. Do they even make them or would Mr. Quang have to use a 30 amp outlet which would force him to rewire with 10/3 AWG and a 30 amp breaker.

Believe me I'm not trying to be a pest, I am trying to understand your logic over mine.

Okay, this brings up a question... again.

Given that have a 12/2 wg, can I use the bare for neutral and share the ground off the oven sitting right below the microwave? I know I asked this in the original post.

Note that there is an oven using 10/3 wg right below where the microwave goes.

No,

Look at the installation instructions, they are tying Neutral to ground on the appliance. You would be using the bare wire as both neutral and return.

By the way, Are you sure that your home is on a three wire drop or lateral? How do you know this for sure, have you been inside the main panel and verified that there are two power lugs and only one Neutral wire and bus bar?

If you actually have four wire, then your only option is to remove the 12/2 and run 12/3 and all this dialogue, while very interesting, particularly to me, would become pointless.

Hook up the Black to breaker, Identify white as red or black, connect to Breaker, Neutral and ground to ground. You should already be cooking. Don't let it all get confusing. Use the Metal plate with Greenfield connector, and call it a day.
This is 100% flat out WRONG.
Do whatever you want, but this is WRONG.

Telling someone to use the bare ground of an NM cable as a current carrying neutral is NOT a very smart thing to do. If something bad happens because of this, and this is quite possible, where will you be??

To QN. The information I have given you is code correct. I have provided facts to back it up. Whether you follow this or other information is up to you.

Good luck.

OK Don, I'll try to explain the best I can.

The three wires coming into your house are indeed two hots and what is correctly called the grounded conductor. The layman's term for the grounded conductor is "neutral".
There is NO "grounding" conductor coming in from the utility. You will never have a "4-wire" drop from the street. The POCO will never provide a grounding conductor.

A "grounded conductor" is one that is intentionally grounded at some point. This is the conductor that carries the current imbalance of the two hot service wires. This is also what gives us 120 volts at our service instead of just 240v.

A grounding conductor, or more correctly, "equipment grounding conductor" is NOT the same thing. Here is a definition:

Grounding Conductor, Equipment. The conductor used to connect the non–current-carrying metal parts of equipment, raceways, and other enclosures to the system grounded conductor, the grounding electrode conductor, or both, at the service equipment or at the source of a separately derived system.




At the main service disconnect the two are bonded, meaning they are connected together mechanically and electrically. This is the ONLY Place that they are bonded.

A bond neutral to ground bond downstream of the service equipment can be a very dangerous thing. Metal parts of equipment can become energized. Connections can arc and spark. Splices and connections can become hot to the point of fire.
If they are bonded, or if the ground is used as a neutral, the grounding can and will carry current. THIS is what makes it dangerous.
An equipment grounding conductor is NOT meant to carry current.

To QN. The information I have given you is code correct. I have provided facts to back it up. Whether or not you follow this or other information is up to you.
Good luck.

Even if I wanted to the technician and inspector are not going to let it happen. I'm not in a hurry. I rather be late and have it done right the first time.

Thanks for your suggestion.

I rather be late and have it done right the first time.Good call. :)

...Given that have a 12/2 wg, can I use the bare for neutral and share the ground off the oven sitting right below the microwave?....

No. Period. stanfortyman explained that way back in the post where he gave the only exception to that is SE cable. You have NM. NO again.

Okay,

Explain for me, for my own edification, why the same arrangement is allowed to run 10/2 240 VAC using the taped white as L2 to a baseboard heater? Because that's what a licensed electrician did in what is now my office, really it was a shed, but because I make too much noise, it became my office.

At least according to the last owner, the work was done by a licensed electrician. As a matter of fact, he did a home run from the heater to the SEP for the heat, then installed a home run from a sub panel in the office tied back to a different 240 VAC breaker. That sub panel is wired with two 120 vac -30 amp (thin lines) and one 120 vac 20 amp breaker.

Is it because the floor baseboard heat does not need a 120 VAC as the does the convection microwave?

Qn, If you get your 4 conductors from panel to Micro, their can't be any argument.
If the Oven is in Conduit, you may be able to pull additional wires through there, then fish up to micro. Good Luck

Is it because the floor baseboard heat does not need a 120 VAC as the does the convection microwave?Exactly.
Things like a baseboard heater, water heater, bigger electric motors, A/C condensors, all are straight 240v loads. The circuits they use require NO neutral.
In these cases the use of "2-wire" type cable (ie: 12/2, 10/2, etc) is acceptable and typical.

Well, why didn't you write that out in English for me to misread earlier? :)

Thanks

Those instructions are the worst I've seen. The three wire instructions say to connect 4 wires and the 4 wire instructions say to connect 4 wires. The only thing I see different is the picture. Please confirm that.

It sounds like it's the range case and the 4 wire range connected to a three wire supply requires that white/bare of the oven be conncted to bare of the feed. Red is connected to L2, Black is connected to L1. L1 and L2 are Line 1, Line 2 or hot1 and hot 2.

Is that what everybody gets now that it's OK with tk that a 3 wire feed can be used for a 4 wire appliance in this configuration?

Those instructions are the worst I've seen. The three wire instructions say to connect 4 wires and the 4 wire instructions say to connect 4 wires. The only thing I see different is the picture. Please confirm that.

It sounds like it's the range case and the 4 wire range connected to a three wire supply requires that white/bare of the oven be conncted to bare of the feed. Red is connected to L2, Black is connected to L1. L1 and L2 are Line 1, Line 2 or hot1 and hot 2.

Is that what everybody gets now that it's OK with tk that a 3 wire feed can be used for a 4 wire appliance in this configuration?Yes, I agree that those instructions are terrible.
For one thing they only say 240v, when it is NOT "240v", it is 120/240v. The stupid "3-wire" and "4-wire" terminology is what is causing this WHOLE mess.

Also, they are NOT saying "that white/bare of the oven be conncted to bare of the feed."

Here is the quote from the instructions for the "

Here is the quote from the instructions for the " hookup:

"2. Connect the 2 white wires (D) and the green (or bare) ground
wire (of the microwave oven cable) using a UL listed wire
connector." hookup:

"the two white wires"

They say "of the microwave oven cable" is VERY important.

They probably should say; 240 for existing compatible wiring. 120/240 for new wiring.

Not really. The oven DOES require 120/240v, and even an older circuit still is 120/240v. It just lacks a dedicated ground.

qn, If you get your 4 conductors from panel to Micro, their can't be any argument.
If the Oven is in Conduit, you may be able to pull additional wires through there, then fish up to micro. Good Luck

I checked. It's not it a conduit, and it's nailed to the studs. :(

Yes, I agree that those instructions are terrible.
For one thing they only say 240v, when it is NOT "240v", it is 120/240v. The stupid "3-wire" and "4-wire" terminology is what is causing this WHOLE mess.

Also, they are NOT saying "that white/bare of the oven be conncted to bare of the feed."

Here is the quote from the instructions for the "3-wire" hookup:

"2. Connect the 2 white wires (D) and the green (or bare) ground
wire (of the microwave oven cable) using a UL listed wire
connector."

They say "the two white wires" when they mean the white from the oven and the white from the feed. The point is that the ground FROM THE OVEN gets bonded to the neutral in the case of an existing legal 3-wire circuit.
The term "of the microwave oven cable" is VERY important.


If you guys are confused, a typical guy like me without much of electrical wiring background would be much, much more confused.

But you picked up on it. I mostly follow the motto "If all else fails, read the instructions".