Can I do this with the wiring of my double oven?

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  #1  
Old 03-21-12, 08:16 PM
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Can I do this with the wiring of my double oven?

I am replacing a stand-alone range with an older GE double oven. It is on a 40
amp circuit and according to the electrical requirements plate, 40 amp is sufficient. I assumed that I had 8 gauge wire so I went and bought the 10' extra that I
needed to move the double oven to its new location. When I went to connect the existing wire with the new 8 gauge, I realized that the new wire is undersized. I
am guessing that the existing wire is actually 6 gauge NOT 8 gauge.

So, can I step down to a 8 gauge wire for the last 8 feet in an approximate 60' run from the panel?

I was going to put a 4x4 box in the crawl space and then run the new wire from
the box to the oven using the new wire.

What do you think?
 
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  #2  
Old 03-21-12, 09:36 PM
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Unless your original wiring is a four-wire configuration (2 "hots", a neutral and an equipment grounding conductor) you may not extend it at all.
 
  #3  
Old 03-22-12, 05:31 AM
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it is not 4 wire. it has only a black, red and white. I was going to connect the
ground from the appliance to the white from the service along with the white from
the appliance.

please help me understand why i cant extend the line another 6 feet using the
original wiring configuration.

thanks
 
  #4  
Old 03-22-12, 06:58 AM
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it is not 4 wire. it has only a black, red and white. I was going to connect the
ground from the appliance to the white from the service along with the white from
the appliance.

please help me understand why i cant extend the line another 6 feet using the
original wiring configuration.
Modern code requires a four wire feed to an appliance. If an installation is old enough a three wire feed is grandfathered but it can not be extended. Because you are extending it you must replace with a four wire feed. Code does permit you to add a ground wire but it would probably be just as easy to add a new cable though depending on distance not as cheap.

Above assumes a 120/240 volt oven. If it is a 240 volt only oven only a two wire cable with ground feed (3 wires) can be used but you don't have a ground. The ground must be factory colored green, bare, or green/yellow on #6 and smaller. White can not be used so again you would need to add a ground or run a new cable.
 
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Old 03-23-12, 03:07 PM
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>>I was going to connect the ground from the appliance to the white from the service along with the white from the appliance.

please help me understand why i cant extend the line another 6 feet using the
original wiring configuration.<<

Because, in addition to what's already been said about your needing both a ground and a neutral from the panel to the load, you may not, repeat NOT, tie neutral to ground, nor ground to neutral, anywhere beyond the service entrance.

There a long-winded explanation of why this is so, but the short answer is that it creates a potentially dangerous, possibly even lethal, condition. Electrical code requirements are all about keeping us safe from the lightening we have brought into our homes and workplaces. Remember that we humans are excellent conductors of electricity, and weigh that against the savings in money and time that any short cut or work-around might gain you. Please.
 
  #6  
Old 03-23-12, 06:29 PM
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Thanks nashkat. I can tell your advice is just out of concern to keep us safe. I
Appreciate it.

I have decided to run a new wire from the panel to the oven. I will use the
existing 40 amp breaker. I also want to install a counter cooktop which I believe
requires a 50 amp breaker. I will also run a new circuit for that.

So, my question is since I would like to buy the same guage wire for both new
circuits: what gauge wire will cover both applications if the length of
the run is about 60 feet?

I was thinking a 6 gauge 3 wire with a ground.

Thanks
 
  #7  
Old 03-23-12, 07:20 PM
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The 40A line will use Copper 8/3G while the 50A will use 6/3g.
 
  #8  
Old 03-23-12, 08:58 PM
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Can I use 6/3G for both so I can just buy one spool for both?
 
  #9  
Old 03-23-12, 09:27 PM
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Last I checked, the shortest spool of wire available in that size was 250 feet. That's a lot of wire for two 60' runs.

There are also conductivity and resistance-related reasons for not oversizing conductors.

If you're trying to save money, why don't you treat the oven and cooktop together as "a range" and run only one cable, install only one breaker, and tap the ovens off the home run?
 
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Old 03-24-12, 05:35 AM
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Can I use 6/3G for both so I can just buy one spool for both?
Yes, you can. Your "6/3G" gives me the impression that you are planning to run some NM-b cable. If this is true, you can buy it by the foot (very expensive). Otherwise, I see if you are in Indiana. Your local Menards will carry short rolls of these cables (8/3+g and 6/3+g) in 15', 25', 50' and more lengths. That would be better and cheaper then buying all #6.
 
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Old 03-24-12, 06:08 AM
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Last I checked, the shortest spool of wire available in that size was 250 feet. That's a lot of wire for two 60' runs.
I am not a Home Depot fan, because I think their wire prices are almost always too high. That being said, they do stock 125 foot rolls of 6-3 NM-b cable that would provide you more than enough to make two 60 foot runs and not have a lot of waste.

Nm-B Cable from Southwire | The Home Depot - Model 63950002

Most other big box stores should stock 125 foot rolls of both 6-3 and 8-3 NM-b cable.
 
  #12  
Old 03-24-12, 09:11 AM
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I like the idea of tapping off but how does it work?

If both appliances need different amperage, one needs 50 and one needs 40, how do I handle that?
 
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Old 03-24-12, 09:25 AM
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I like the idea of tapping off but how does it work?
Basically you treat the combined devices as a single cooking appliance just like you were installing a stove that had both both burners and an oven. You add the actual max amps of both together to get the amps need for your "stove". Then install a breaker and cable to supply that "stove". At the kitchen you can either wire both to the feed in the same box or branch off to each appliance using cable sized to the breaker.
 
  #14  
Old 03-24-12, 09:27 AM
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There's a recent discussion here titled Is a 60A circuit sufficient for a cooktop and double oven?
 
  #15  
Old 03-24-12, 09:45 AM
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Thanks again for the advice and I would like to do the tap off thing but...

If I add up the max output for both devices I am at close to needing a 100 amp breaker ( or a little
less), that seems way too big and I can only imagine what size wire I would need for that.

Am I not understanding something here?

Btw: nashkat, I read that thread a few weeks ago, I found it interesting. Thanks for the link.
 
  #16  
Old 03-24-12, 11:47 AM
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You would not total the amps of the circuit breakers, you total the amps of the appliances which is found on the nameplate. Basically you are just treating the wall oven and cook top as one unit. Just like a combined range.
 
  #17  
Old 03-24-12, 01:58 PM
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Okay, let's get down to the nuts and bolts:

The double oven is 6.8kW @ 120/240V

The cooktop is 9.6kW @ 120/240V

So, what size breaker and wire?

Thanks!!!!
 
  #18  
Old 03-24-12, 02:36 PM
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Forget the idea of using a single branch circuit for your two appliances. While technically feasible you would need to use a #4 (copper) cable and THAT most likely would not be cost effective.
 
  #19  
Old 03-24-12, 03:29 PM
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I agree with Furd. Run two branch circuits. One #6 wire (50 amp) and one #8 wire (40 amp).
 
  #20  
Old 03-24-12, 03:44 PM
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Ok but...

Not wanting to waste wire and not exactly sure how long the runs will be, can I just go with 6g for
both circuits? That allows me to buy one spool.
 
  #21  
Old 03-24-12, 04:11 PM
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Forget the idea of using a single branch circuit for your two appliances. While technically feasible you would need to use a #4 (copper) cable and THAT most likely would not be cost effective.
Furd,
can you explain how you got to a #4 Cu?? Just wondering.

@ robert,
doing a tap should be the last thing you want to do!! Although I’ve given calculations for it for another poster, I would highly recommend against it, for DIYers. I agree with the others. Go with two circuits. I believe you should take some measurements, and see if one roll of #6 will work. I believe a roll of #6-3 with ground NM-B is 125 feet long. If one roll can’t be divided (x2), then a roll of #6, and a roll of #8 —as others have mentioned--will be your best bet. Some places sell it by the foot. Do the calculation—based on your measurements—to see if you can save by buying per foot. Normally the per foot cost is higher, but if you need 70 feet per run, you may save.
 
  #22  
Old 03-24-12, 04:33 PM
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9.6 kW + 6.8 kW = 16.4 kW = 16,400 watts.

16,400 watts divided by 240 volts = 68.33 amperes.

Maximum current for #6 copper conductors (cable or conduit) at 75 degrees C. = 65 amperes.

Therefore, #4 copper conductors minimum size. Perhaps there is a load factor allowance that I have not included that would allow the use of #6 conductors but highly unlikely with type NM cable.
 
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Old 03-24-12, 04:47 PM
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9.6 kW + 6.8 kW = 16.4 kW = 16,400 watts.

16,400 watts divided by 240 volts = 68.33 amperes.

Maximum current for #6 copper conductors (cable or conduit) at 75 degrees C. = 65 amperes.

Therefore, #4 copper conductors minimum size. Perhaps there is a load factor allowance that I have not included that would allow the use of #6 conductors but highly unlikely with type NM cable.
You did the calculation right, but this calculation doesn’t apply to the allowed tap rule—where cooking appliances are being served from one OCPD.

So:
Per NEC T. 220.55 Note 4 we are allowed a demand in this case. So we get:
>16.4kva-12=4.4
>4.4(.05)=.22
>8kva(.22)=1.76kva
>8kva+1.76kva=9.76Kva
>9760va/240v=41A
 
  #24  
Old 03-24-12, 05:17 PM
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I'm not defending my original answer but you might want to check out the discussion held some six years ago.

http://www.doityourself.com/forum/el...ange-wire.html

At one point in that discussion it was pointed out that Article 220.55 (which doesn't even appear in my 2002 code book) applies to services and feeders, not branch circuits.
 
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Old 03-24-12, 05:40 PM
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I'm not defending my original answer but you might want to check out the discussion held some six years ago.

Range wire

At one point in that discussion it was pointed out that Article 220.55 (which doesn't even appear in my 2002 code book) applies to services and feeders, not branch circuits.
I agree, the demand factors are for feeders and service loads, but Per T.220.55 Note 4, it permits a demand for branch circuits—where it applies to the install. See Table 220.55 note 4<<<there is no defense against it, it’s clear Note: I did not read your link. As I believe code is clear in this case.
 
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Old 03-24-12, 05:46 PM
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To add: it is in the 2002, 2005, and 2008 NEC code books.
Edit to add: i took a look at the link, and don’t understand why all the confusion. I believe we over think things some times, but obviously over thinking is needed for some portions of the code, and the cooking appliance calculations is one of them.I just believe this portion ( where Note 4 applies) isn’t one. But then again, what do I know…..LOL
 
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Old 03-24-12, 06:12 PM
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Looking a bit more closely at my 2002 NEC I find that it is under Article 220.19. In the 2002 NEC there is no Article 220.55; it goes from 220.41 to Article 225.

Obviously I need to refrain from making absolute statements concerning the latest code revisions.
 
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Old 03-24-12, 06:18 PM
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Looking a bit more closely at my 2002 NEC I find that it is under Article 220.19. In the 2002 NEC there is no Article 220.55; it goes from 220.41 to Article 225.

Obviously I need to refrain from making absolute statements concerning the latest code revisions.
I agree, the Table with notes is under 220.19 in the 2002. I had to go get my 2002, it was in the garage attic . But, as stated, it is in the last three code books. Happy you found it!!
 
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Old 03-24-12, 06:21 PM
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@ Furd,

why aren’t you out enjoying the sun. Seems Washington is looking bright today
 
  #30  
Old 03-24-12, 06:22 PM
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Physical limitations are preventing that. I do need to hobble over to the door and get the cat inside before it gets dark.
 
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Old 03-25-12, 12:53 PM
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IC, sorry to hear.

Seems it want last, so you want be missing much!!
 
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Old 03-25-12, 05:00 PM
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If you all are still there, I have another (related) question.

I am installing 2 circuits like we discussed. There are 2 main panels in the garage and if I move some circuits, I can open up a space for 2 double pole breakers. The panels are recessed into the wall and the wires go up (inside the wall) to the attic space. What is the best way to access the wiring when the panels are recessed?
Cut back the Sheetrock?
 
  #33  
Old 03-25-12, 05:40 PM
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You can buy ready made access doors and permanently set one in place above the panels. At big box check plumbing not electrical for them.
 
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Old 03-25-12, 06:06 PM
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Yep. I have been known to remove the wall covering from panel to ceiling and from stud center to stud center and then replace it, once I'd completed the electrical work, with a piece of smooth-surface plywood mounted with trim screws or, in one case, with the cedar paneling I'd removed, battened together on the back and mounted to the studs with brass screws and trim washers. In each case I had an accessible wireway for future use.
 
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Old 03-25-12, 06:09 PM
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An appealing thought, Ray. I'll keep this in mind.
 
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Old 03-25-12, 07:54 PM
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I am wondering how you cut the Sheetrock from center of stud to center of stud. When I try that I end up hitting Sheetrock screws and the edges are ruined. The
garage drywall is taped and mudded, the screws are not exposed.

I usually cut inside stud to other inside stud and then install sister studs and replace Sheetrock with the piece I cut out. However, I believe putting in sister studs
would be tough with the presence of wires in that stud bay.
 
  #37  
Old 03-25-12, 09:00 PM
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Yes, Robert, I think it would be a challenge to install sistered studs in a stud bay that is a wireway. I cut drywall down the center of a stud with a utility knife. If I'm dead center I rarely hit a nail or screw but, when I do, I stop to remove it and then continue. I find it helps to uncover the space in sections, leaving the top wall-to-ceiling tape joint until the last -- if I have to cut that at all.
 
  #38  
Old 03-25-12, 11:37 PM
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I cut the drywall to inside the stud space and then add "listings" on the studs to hold the drywall back in place. The listings are considerably less depth than a full stud and I have never had a problem installing them with screws through pre-drilled holes. This also gives me a much broader area for attaching the new, or replaced, drywall than trying to half-lap it on a stud sharing another piece of drywall. Even if you have cables going through the studs horizontally you can use this method as the listings don't have to be continuous for the entire length of the stud.
 
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