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  #1   IP: 157.134.170.40
Old October 29th, 2002, 08:34 PM
Tom L. Tom L. is offline
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Default Split oven/stove wiring

I am supplying new service to my stove/oven. The current wiring (8 gague) comes into a junction box below the stove. There it splits off to go to the oven (8 gague run) and the stove (10 gague run).
I am only replacing up to the junction box. The wires from the junction box to the stove and oven will stay the same. My new supply run will be 8 gague

In the junction box each wire is connected by a connector that looks like a nut/bolt with a slot in it. It is then wrapped in electrical tape. This was done about 50 years ago. Is there a more 'modern' method of connecting wires of this size (2 8 gague and 1 10 gague).
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  #2   IP: 148.78.248.10
Old October 30th, 2002, 12:20 PM
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Wgoodrich Wgoodrich is offline
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The following option is only allowed if all conductors are copper conductors.

Ideal makes a wire nut called a blue wing nut that will connect two 8 awg and one 10 awg copper conductor. It is a big wire nut that you make all conductors even without twisting then just screw the blue wire nut on those three wires. The plastic of the wire nut is approved to be used as the insulation for that connection.

I do question what you are doing, not sure.

Are you connecting an oven and a counter mounted cook top with top burners only and no oven as part of the cook top? Are you connecting an oven and a free standing range that has the top burners and a built in oven in that free standing range making two ovens?

If you are connecting a free standing range with top burners and a built in oven and a second oven to run off that 8 awg copper branch circuit you will be exceeding your amp rating of your 8 awg branch circuit that is required to be protected by a maximum of 40 amps. If you are installing a free standing range with a built in oven and a separate oven you need a minimum of a 6 awg copper branch circuit to carry both loads. If this is what you are doing then I suggest you install either a new 8 or 6 awg copper branch circuit with a black red white and bare to serve that free standing range and use the old branch circuit to serve the oven.

Be aware that installing a new oven or range causes you a concern when connecting to an existing branch circuit. This existing branch may be a three wire branch circuit but that existing branch cirucit requires it to contain either a black red and white or a black red and bare. You must not continue using a black white and bare cable to serve a new range.

Also if you only have three conductors and only if you have one of the two above that is approved and not the one above that is forbidden to be use then you must make a change in the oven and range if either is new oven or range. If you use the existing black white and red or black red and bare cable for a new oven or range then you must install a jumper between the neutral bar of the terminal block found inside that oven or range and jump from that silver screw in the center of that terminal bar found inside the range or oven jumped to the metal frame of that range or oven.

Be careful

Wg
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  #3   IP: 157.134.170.9
Old October 30th, 2002, 07:47 PM
Tom L. Tom L. is offline
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All of the wiring is copper

The stove (cooktop) is just a 4 burner cooktop, no oven. The oven is just a oven. Both are seperate units with seperate power sources.

It appears to be fed with 6 gague wire on a 40 amp breaker. In the junction box below the stove it splits to 8 gague to the stove, and 10 gague to the oven. Both the stove and oven are 3 wire (red, black and white). The feed is red black and bare.

What I am doing is moving the stove/oven from the sub panel that it currently is powered from, to the main panel. In doing so, I am upgrading the supply wire to 4 wire (red black white bare). However I am not planning to pull out the oven or the stove to upgrade the 2 supply lines from the junction box to the appliance itself. This will be done in a upcoming kitchen remodel.

First off.. They had 6 gague wire on a 40 amp circuit. It is copper. I am assuming that going to 8 gague would be ok since it is 40 amp rated.

Next.. with a 4 wire supply and 3 wire appliances (for now) where I can not get access to seperate ground from neutral at this time. Red to red and black to black of course. Then white goes to ........? (white, bare or both). When I do get access to the appliances, I will split he ground/ neutral in the junction box and on the units. These are built in units and it may involve some minor destruction to the kitchen to pull them to access the wiring. It is not possible at this time
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  #4   IP: 148.78.248.10
Old October 31st, 2002, 03:26 PM
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YOU SAID;
The stove (cooktop) is just a 4 burner cooktop, no oven. The oven is just a oven. Both are seperate units with seperate power sources. It appears to be fed with 6 gague wire on a 40 amp breaker. In the junction box below the stove it splits to 8 gague to the stove, and 10 gague to the oven. Both the stove and oven are 3 wire (red, black and white). The feed is red black and bare.

REPLY;
From your discription you have a 60 amp 6 awg copper branch circuit with a black red and white wire feeding from a 40 amp breaker that is allowed to be a 60 amp breaker in the panel instead of you 40 amp breaker if you need it to be heavier. This 6 awg branch circuit is then tapped two directions with different size taps using the cooking equipment tap rule that the NEC allows. Then you say you have an 8 awg to the cook top and a 10 awg to the oven. This concerns me a bit. The cook top should be your 10 awg and your oven should be an 8 awg conductor. You are saying exactly the opposite of what it should be. Please check to confirm If you have an 8 to the cook top that would be fine but is allowed to be a 10 awg tap. If you have a 10 awg tap from your junction box to the oven then this wire is too small and is required to be a minimum of 8 awg. Please confirm if your oven is a double oven or a single oven then open your oven door and look for a name plate on that oven by the oven door seal normally. Look to see what the minmum amp branch circuit is required for that oven. This concerns me a bit.

YOU SAID;
What I am doing is moving the stove/oven from the sub panel that it currently is powered from, to the main panel. In doing so, I am upgrading the supply wire to 4 wire (red black white bare). However I am not planning to pull out the oven or the stove to upgrade the 2 supply lines from the junction box to the appliance itself. This will be done in a upcoming kitchen remodel.

REPLY;
Your three wire 6 awg wire cable with a black red and white wire is fine concerning existing and the rules of the NEC. Running a 4 wire cable is not suggested in my opinion. When you decide to upgrade to a four wire cable then run a new four wire cable from your panel to the junction box where the appliances are located. Problem that concerns me with your upgrading plan to 4 wire is that you are implying that you are going to make a second junction in this 4 wire cable when you plan to extend from there to the cook top and oven at a later date. You need to be aware that appliances using resistant heat such as cook tops and ovens are terrible on creating loose connections in junctions of that branch circuit. While the NEC allows the 6 awg to be junctioned it is not advisable because of a track record of loose connections at junctions in a branch circuit serving an appliances using resistance heat. If you plan to make a new four wire branch circuit then run that four wire all the way to the oven and range junction box. Better yet run a new 8 awg four wire branch circuit to your oven and a 10 awg or even an 8 awg four wire to your cooktop ran nonstop from the panel to the cook top then from the panel to the oven. While the NEC approves what you are doing you will eventually experience enough savings in electrical usage to pay the extra money invested and experience long time trouble free appliance use.

As for not being able to get to your range or cook top connection you should be able to fish from your panel into the crawl space then up into the cabinet under the oven then under the cook top now. Then when you upgrade your cabinets just turn off the breakers and remove your cabinets and install new cabinets and reinstall the junction box serving each oven and cook top that is requried to be accessible. Your connections to these appliances if installed within NEC rules should be found in the cabinet below the oven and cook top.

YOU SAID;
First off.. They had 6 gague wire on a 40 amp circuit. It is copper. I am assuming that going to 8 gague would be ok since it is 40 amp rated.

REPLY;
tHE 6 AWG wire is allowed to be protected by a 60 amp breaker maximum. If the 40 amp breaker holds then you are fine. The NEC allows you to serve both appliances from one branch circuit being a 6 awg existing 3 wire branch circuit with a black, red, and white in that existing cable and is allowed to be used with modefications to new equipment. The NEC recognizes short pieces of cable not longer than necessary that is sized no smaller than 1/3 the ampacity of the 6 awg branch circuit. This is called an appliance tap rule allowing 10 awg wire to the cook top and 8 awg wire to the oven with the 6 awg feeding both as two taps from that 6 awg wire.

YOU SAID;
Next.. with a 4 wire supply and 3 wire appliances (for now) where I can not get access to seperate ground from neutral at this time. Red to red and black to black of course. Then white goes to ........? (white, bare or both). When I do get access to the appliances, I will split he ground/ neutral in the junction box and on the units. These are built in units and it may involve some minor destruction to the kitchen to pull them to access the wiring. It is not possible at this time

REPLY;
Look under your oven and cook top. You should find metal flex conduit coming from the cook top and coming from the oven down into the cabinet below the oven and cooktop. This is where the connections should be made.

NEVER CONNECT A WHITE TO A BARE WIRE PERIOD, WAY TO DANGEROUS.

As suggested previously in the if you are going to run a new 4 wire cable try to run it with no junctions to the point of the appliance tap or better yet run two new branch circuits one 10 awg or 8 awg four wire branch to the cook top for future option of installing a free standing range in the future is so desired and an 8 awg four wire branch circuit to the oven expecially if a double oven.

You can do as you are suggesting but you are creating a junction in the future when you remodle you kitchen. You should be able to get to the junction boxes where the oven or cook top is connected by looking in your cabinets below the appliance. This is where they are normally connected to the cook top and oven.

IF you must run the 4 wire cable as you suggest DO NOT USE THE BARE WIRE AT ALL UNLESS YOU RUN ALL THE WAY TO THE COOK TOP OR OVEN.

If you use a three wire cable that is existing then in the new cook top and new oven you must install a bonding jumper between the silver center screw of the appliance terminal block found in the oven or cook top to the metal case of that appliance.

You must not install a three wire cable to an oven or cook top without bonding the center screw of the terminal block [silver screw] to the metal frame of the appliance.

If you install a four wire cable all the way from the panel to the appliances then you must install the green wire to the metal frame and your silver screw of the terminal block must then be isolated from the metal frame of the appliance when served by a four wire cable including the bare or green wire in that branch circuit.

You can not connect the bare to the white at any location inside your home except inside the main service rated panel.

Good Luck

Wg
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  #5   IP: 157.134.170.18
Old October 31st, 2002, 08:49 PM
Tom L. Tom L. is offline
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I double and tripple checked.. got 8 gage to the cooktop and 10 gague to the oven.

Nameplate on the oven says 120/240 volts 5.3 Kw 5.3Kw at 240V is about 22 amps. I have not located the nameplate for the cooktop yet. I'm thinking its somewhere on the back.. The unit mounts on the wall and flips down onto your countertop. Its a 1950's Frigidare...made about 15 minutes from my hometown. Restoration parts are readily available.. Its a very unique unit.. Front plate says 'Frigidare Made only by General Motors'

As for the 6 gague supply.. Its gone.. doesnt exist anymore.. It WAS supplied from a sub-panel.. IT will now be supplied by my main service panel. This means a entire new wire from the panel to the junction box below the cooktop where the circuit splits. I have always had intention to make this a continuous run with no breaks between this junction box and the service panel. I was wanting to get the 4 wire upgrade done and over with since I have to move the wire now anyways.

I was not planning to pull the oven and stove off/out of the wall to update the line from the junction box to the appliances (about 3-4 feet each leg). This will be done when the kitchen is remodeled. When I do this I will be able to split up the neutral and ground connection on the back of the units (currently I cant even see this connection..

We never had a problem with the 40 amp breaker tripping...so we will downgrade to 8 gague wire with a 40 amp breaker in the main panel.
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  #6   IP: 148.78.248.10
Old October 31st, 2002, 09:16 PM
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Wgoodrich Wgoodrich is offline
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YOu would not be saving noticable money to run you 6 awg and it would better meet the NEC. You are running two appliances from one cable. Teh 8 would work with what you have but hte 6 would give you and option to upgrade to a free standing range in the future if you like. You choice.

Your blue wire nuts should make your connections. Seems they are most commonly used over split bolts.

Sounds like you are doing fine.

Good Luck

Wg
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  #7   IP: 157.134.170.15
Old November 3rd, 2002, 04:13 PM
Tom L. Tom L. is offline
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Here's an update on my cooktop/oven project.

I finally found the nameplate for the cooktop. (was buried under a blob of grease under a burner.) It is a 7Kw unit.

The oven is a 5.3Kw unit.

The 7Kw cooktop is currently being fed by 8 gague wire with a run of about 3 feet from the junction box where it splits from the feeder.
The oven is being fed by 10 gague, about the same length.

Should I keep the same size wires going to these units from the junction box? Am I safe with a 40 amp supply to this setup?
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Old November 3rd, 2002, 04:44 PM
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8.4 Kw if calculated by 220.19.note 4 or 8.13 Kw if calculated by 220.19.note3 .

Either way the load of both the cook top and the oven is rated at 35 amps.

The answer to your question is yes an 8 awg copper branch circuit may serve both appliances.

Now if you looked at the future and you wanted to convert your cook top to a free standing range then run the oven and range on the same branch circuit again using your cooking branch circuit then the 40 amp 8 awg copper conductor will still serve both the single oven and the free standing range according to 220.19.

If you installed the 6 awg copper then you would be that much better off. Your choice.

Wg
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  #9   IP: 157.134.170.7
Old November 3rd, 2002, 08:20 PM
Tom L. Tom L. is offline
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Ok 8 gague will come into a junction box located under the cooktop. From there would I be safe with a 10 gague jumper running to each the oven and cooktop?

As for the feeder? Are there any other advantage of using 6 gague besides future replacements?
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  #10   IP: 148.78.248.10
Old November 4th, 2002, 03:52 PM
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8 awg calculated to be just enough no extra concerning minimum ampacity of the branch circiut serving two cooking units of that size you quoted.

When you put in just the minimum you are meeting the minimum safety standards saying that to be a safe installation. However you wouild not be running necessarily the most economical to run conductor.

The reason that is said is resistance to current flow ratings of a wire causes what is called voltage drop. Voltage drop causes amps or Kw to increase to do the same amount of work Increase of Kw = equals increase of your cost to do the same work. All the above is directly related to efficiency rating creating your cost factor.

Example a 5% drop in voltage due to a resistance of a wire can directly effect what comes out of your pocket book concerning money.

Now you said your oven and cooktop pulled 12.3 Kw combined load.

Now remember that 12.3 Kw is at an apperant voltage of 220 volts as an example. If the conductor is 125' long at 220 volts and 12.3 Kw draw on an 8 awg copper branch circuit conductor you would have approximately 10.87 volts drop in voltage of that branch circuit now you have at the appliances a voltage of 209.13 volts and a voltage drop of 4.94% voltage drop. When the voltage drops 4.94% then you will have to heat approximately 5% longer to acheive the same degree of heat in that cook top or oven that you would receive if you had a full 220 volts to that appliance. This means you heat element can not work as hard to produce the heat required so you will have to run the heat 5% longer to acheive the same temperature as it was designed to put out to cook with at a given temperature setting.

If you check you will be paying anywhere from 6 cents to 8 cents per Kw per hour that you run your cooking equipment.

Now lets say you are cooking a roast for about 4 hours keeping the heat constant at say 400 degrees. Now lets say at normal voltage it would require the heat elements to heat 60% of the time to maintain that temperature in that cooking equipment. We would have to calculate the 4 hours into minutes 60 times 4 = 240 minutes. Then adjust that down to the true heating element working time of 60% times 240 minutes and we would be heating approximately 144 minutes. Then we would have to convert that back into hours getting a heating time with truly 220 volt of 2.4 hours. Then if calculated a 12.3 Kw rating at a true 220 volts we would be charged 29.52 KwH @ 8 cent per KwH costing $ 2.36 to cook that turkey. Now if we have the voltage drop due to that 8 awg wire and its resistance being only meeting minimum size for safety and not for efficiencey then we would have to increast that running time of heat times 5% increase. We could just multiply the $ 2.36 x 5% increase and our cost with voltage drop considered would be 12 cents more to cook that turkey.

Now say you cook on an average about the time to cook a turkey approximately 300 days of the year,taking about the same amount of time at each meal to cook. That $ 2.36 multiplied times 300 days per meal of 2 meals a day your total cost to run that cooking equipment @ the full 220 volts without any voltage drop for that year would be approximately $1416.00 per year.

Now with that 5% increase in cost for the year would be approximately $ 70.80 per year.

Now my question to you that you need to answer yourself is first how many years in the future are you planning to use that new cooking equipment ? Then multiply that added 5% cost of electricity of approximately $70.80 per year savings if you pay the extra for the 6 awg instead of the 8 awg wire multiplying that savings per year times that many years of planned use of that new cooking equipment.

Now you should do some comparitive cost work. Just how much more on initial investment would 6 awg copper wire cost more than 8 awg copper wire cost.

Think of the initial difference in cost of that wire over the planned life use of that equipment, when installing the larger 6 awg branch circuit instead of hte minimum safe 8 awg branch circuit.

Now compare that added cost of of the 6 awg wire more than the minimum safe 8 awg wire that will cost you the day of installation compared to how much more it will cost you if you don't increase the size of that wire to 6 awg then run that equipment at that extra 5% cost increase due to that voltage drop for that number of years you plan to use that new cooking equipment.

When you get done thinking it over what is said above you probably will decide it worth spending the initial extra money.

Let us know about how many years it would take to get you extra cost back from your increase in wire size initial installation cost.

Just curious

Hope that helps you see that wiring just minimum safe is not necessarily to your best interest.

Good Luck

Wg
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