Prep Wire for electric wall oven and microwave

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  #1  
Old 04-06-07, 03:09 PM
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Red face Prep Wire for electric wall oven and microwave

Hey guys i Know plenty about electrical. Got my trusty NEC 2005 book right here for confirmations ect... and unlike inspectors I have some common sense to interpret the codes correctly :P (= Just kidding). That being said I am not as familiar with the available wall ovens and built-in microwaves from special order and box stores. I just finished my framing and convenience outlets ( yea yea 20A GFCI yadda yadda) and now i would like to wire for my future oven and microwave needs before I close up the wall. I have seen ovens in the 30A 220V and microwaves in 15A 120 but before I wire a 10-3 and a 14-2 for this maximum I was wondering if anyone could tell me what the top range of amperages is for such appliances so I can oversize my wires accordingly and not have to do it later if i upgrade at some point. (and of course, I will just use the proper, lower amperage breaker for now)
 

Last edited by BenfranklinPA; 04-06-07 at 10:36 PM.
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  #2  
Old 04-06-07, 03:26 PM
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Most built-in microwave ovens and microwave-rangehoods require a 20A 120V dedicated circuit wired with 12/2 cable. I've never seen a residential microwave that requires a larger circuit.

Nearly all built-in ovens require a 30A 240V circuit wired with 10/2 cable. I suppose there could be some models that are larger or that require 120/240V supply, but I personally haven't seen them.
 
  #3  
Old 04-06-07, 03:33 PM
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You would be foolish to wire for just about any built in 120 volt appliance with smaller than 12 gage wire. Sure, a 15 amp circuit may be enough now, but what about the future? Wire the microwave for 20 amps. Perhaps use a 15 amp breaker if you wish, but use 12 gage wire.

As for an electric oven, have you thought about a double oven? I have not researched them, but I can certainly imagine one that might need more than a 20 amp circuit. I would wire for an electric oven with at least 8 gage wire, perhaps even 6 gage. Again, use a smaller breaker if necessary, but use larger wire.
 
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Old 04-06-07, 03:57 PM
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hehe.. I only use 14 guage for lighting. most of my 15A outlets and appliances are oversized to a #12-2 with a 15 A breaker. my main question was about the max appliance amperages. I just blurted out #14-2 since I was thinking about a 15A branch circuit.. force of habbit sorry.

Depending on the price difference I will most likely oversize the 220V/30A branch to a #8-3. its only 40-50 feet, so derating the distance is minimal. but the attic does get hot and the rating for NM-B assumes the 60 degree celcius table.

Thanks guys
 
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Old 04-06-07, 04:00 PM
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Originally Posted by racraft View Post
You would be foolish to wire for just about any built in 120 volt appliance with smaller than 12 gage wire. Sure, a 15 amp circuit may be enough now, but what about the future? Wire the microwave for 20 amps. Perhaps use a 15 amp breaker if you wish, but use 12 gage wire.

As for an electric oven, have you thought about a double oven? I have not researched them, but I can certainly imagine one that might need more than a 20 amp circuit. I would wire for an electric oven with at least 8 gage wire, perhaps even 6 gage. Again, use a smaller breaker if necessary, but use larger wire.
do you think a #6-3 will ever really be nessary (thats the reason im posting) #6-3 is a HUGE price jump and if I (or a future owner) ever got a double oven I would have to 86 the microwave as its only a 12'x12' kitchen with 2 doorways.

Assuming it will always be a single wall oven is a 8-3 enough.

P.S. the oven was the 30A circuit... the microwave was the 20A...
 
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Old 04-06-07, 04:16 PM
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> but the attic does get hot and the rating for NM-B assumes the 60 degree
> celcius table.

I'm not trying to discourage you from upsizing to #8 -- I think that's a decent idea; I'm just giving you some code to mull over.

The conductors in NM-B cable are actually rated to 90 degrees (that's what the B in NM-B means); despite this rating, code only allows NM cable to be installed per its 60 degree rating. In addition to that, the code fixes the 60 degree ampacities of #14, #12, and #10 at 15A, 20A, and 30A respectively even though the "engineering" ampacities are somewhat higher.

The point is that with #14, #12, and #10 NM-B cable in a residential setting, the code has already accounted for a substantial margin of derating by default. It is very rarely necessary to further de-rate these cables based on ambient temperature or bundling.
 
  #7  
Old 04-06-07, 04:20 PM
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> do you think a #6-3 will ever really be nessary

No.

> [me or...] a future owner ever got a double oven

I don't think you should plan for this case unless you're installing a double oven now. It's huge increase in wire cost that will probably never be used. If you (or someone else) ever wants a double oven, they can factor the new wire cost into the remodel project at that time.

> Assuming it will always be a single wall oven is a 8-3 enough.

My opinion is that #10/2 is enough and #8/3 provides a huge margin.

Addition: Upon reflection, I would up my minimum recommendation to #10/3 cable instead of #10/2. While most wall ovens do not require a neutral conductor, I can certainly see how some models might given the multitude of features modern appliances have. It's better to install the neutral conductor and cap it off than to need one and not have it.
 

Last edited by ibpooks; 04-06-07 at 04:31 PM.
  #8  
Old 04-06-07, 05:26 PM
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I've heard that Ge makes a 30" single wall oven that requires a 40 amp connection but I'm with Ben.... most are 30 amp 10 awg connected..even the high end ones. I think you are best served to have the appliances in front of you to know just exactly what is required for the electrical. Trying to wire to cover all the bases for all the different cooking appliances out there is not the way to go imo. I do think that what ever you run for cable should have a neutral needed or not. If you had a free standing range circuit almost all of them can go on a 40 amp circuit but it depends on what the manufactucer requires as to individual circuits and kw requirements. If you think your going to need a double oven someday then it is not unusual for them to be 50 amp circuits. BTW if you have large gatherings for the holidays you or your wife will quickly appreciate a double oven. I think this is what Bob is getting at. You couldn't pry my double viking oven from my wifes cold....well you know what I mean. Of course it's all about money but money well spent and in the right places is well worth the expense.
Do you have a cooktop?

roger
 
  #9  
Old 04-06-07, 09:33 PM
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Cool. Thanks guys. Im box stor shopping so instead of getting the cut at $2 a foot i just picked-up the 125' wraped 8-3 for $135 or so. I figure i can probably use the extra 75 feet for re-wireing my laundry room or something later.

I did not know about the "-b" making that diference for 90 degrees. I got other info on NM... and somone else told me that NM-B follows the same as UF at 60 degrees.
even on spec sheets for sales of NM-B I see "Inner conductors are type THHN, rated 90 degrees Celsius, 600 volts. Solid strands. Outer jacket is PVC rated at 75 degrees Celsius. Amapcity of the product is limited to that for 60 degrees Celsius rated conductors per the National Electric Code... "

by that i think that if i wanted to rate the wire under thee 90 degree table i would have to run #8 thhn in conduit and not a 75 degree romex plastic jacket with 3 conductors overlaping. (especially in my hot attic)

Ill have to look into that -b rating further.
 
  #10  
Old 04-06-07, 09:40 PM
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Rog. I dont have anything yet. Im going Gas for the stovetop, electric for the oven, and converting to pex and PVC for the plumbing. (pipes in cold crawlspace almost froze one year) Right now i got my cement board down, walls open, new larger window installed, Insulation done, wiring almost done.. next thing is to install a skylight and wallboard the ceiling, then walls, then counters and cabinets. and then ill get to the stovetop and oven install

And its not all about money... in my case its more about storage space and cabinets i went from barley any and i want to max my use of space in a 12x12 room. a double oven would waste that valuable real estate. especiall since i know more recipies than my fiancee lol (dont tell her i said that) hehehe.. hey i cant help it . its cultural as well as our upbringing. Im italian, shes jewish... i was brought up in a house where we cooked alot, her mother rarley cooked. I learned to bake pastries and pizzas. she learned how to make stir fry and avoid using yeast on holidays. the double oven wont be missed by her and ill make due as i always do
 

Last edited by BenfranklinPA; 04-06-07 at 09:50 PM.
  #11  
Old 04-06-07, 10:24 PM
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unlike inspectors I have some common sense to interpret the codes correctly :P.

Great way to make friends.

i Know plenty about electrical. Got my trusty NEC 2005 book right here for confirmations ect...

I know people that can't figure how to read it.
 
  #12  
Old 04-06-07, 10:34 PM
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Aww its just alittle razzing.. hehe common.
let me explain where this comes from. imagine you finish a nice job all to 2005 code and then an inspector comes by and rejects you saying that the township uses 1997 code. In a nutshell you have done too good of a job to pass. and then the building inspector critisizes you for oversizing lumber for joists instead of using the mimium as gospel and says your "Overbuilding" when you know your going to have a 200 gallon fish tank on that floor... at what point do you break down and make fun of them alitlle... and then there are some inspectors (not all and not you) that should not have the job in the first place. my inspector in this industrial town dosnt want anything to do with residential. he was acting like i was the fool for calling him (after he finally returned my 5th message 3 weeks later)

I said i can inturpet the code. I didnt memorize the whole thing LOL
 
  #13  
Old 04-06-07, 11:02 PM
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Originally Posted by ibpooks View Post
> but the attic does get hot and the rating for NM-B assumes the 60 degree
> celcius table.

I'm not trying to discourage you from upsizing to #8 -- I think that's a decent idea; I'm just giving you some code to mull over.

The conductors in NM-B cable are actually rated to 90 degrees (that's what the B in NM-B means); despite this rating, code only allows NM cable to be installed per its 60 degree rating. In addition to that, the code fixes the 60 degree ampacities of #14, #12, and #10 at 15A, 20A, and 30A respectively even though the "engineering" ampacities are somewhat higher.

The point is that with #14, #12, and #10 NM-B cable in a residential setting, the code has already accounted for a substantial margin of derating by default. It is very rarely necessary to further de-rate these cables based on ambient temperature or bundling.
Ok i see your referance here. 334.80 says 60 degrees but 334.112 states "... conductor insulation shall be rated at 90 degrees C (194 F) FPN: ...NM-B, NMC-b and NMS-B meet this requirement." stating that NM-B is rated at 90 degrees, or at least i think...

Which is strange since i see things listed as NM-B but has an outer jacket temp of 75 degrees C. linked here:
http://electrical.hardwarestore.com/14-48-building-wire-nm/romex-building-wire-605102.aspx
So that either means that the manufactuers (i.e. ROMEX) can rate there jackets at whatever and 334.112 shall require us to reduce to that temp stated by the manufacturer. or that the manufacturer is not making NM-B at all. but just a higher quality NM that is only "sub" NM-B quality.
Interesting paradox

sum-up
Question is: 334.112 states "... conductor insulation shall be rated at 90 degrees C (194 F)" but what happens when its outer jacket is only rated at 75 degrees?

Nevermind ill post this question in a new discussion just for interest.
 

Last edited by BenfranklinPA; 04-06-07 at 11:14 PM.
  #14  
Old 04-06-07, 11:28 PM
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Aww its just alittle razzing.. hehe common.#

Understood. Can't play the game.. Go home.

that the township uses 1997 code.#

So whats the problem? Your better.

the building inspector critisizes you for oversizing lumber for joists instead of using the mimium as gospel and says your "Overbuilding" #

22 years Never have run into this.

when you know your going to have a 200 gallon fish tank on that floor... #

This is something I don't/can't comprehend! (I love the ocean, It holds ALL my fish,And always there when I want to see them)


then there are some inspectors (not all and not you) that should not have the job in the first place. #

You aint' kidding!!!!!!!!

(after he finally returned my 5th message 3 weeks later)#

Here. 72 HRs, after written notification. This covers the permit ( Tues @ 2 PM on the permit).

I said i can inturpet the code.#

We All can. But.... There is a certain board (here) That will determain If I see it the same as them.

Good luck. over build, That should never be an issue. Just costs you more.
 
  #15  
Old 04-06-07, 11:39 PM
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cool. Sorry i suck so much at sociality, conversation and communication.
If I talk (or type) to you I look like an idiot.
but if you watch me work I look like a genius. (or so I have been told by many people)
I guess everything has to ballance out somewhere I can see an object, theory, numbers and calculations in my mind instantly and easily. Instead of a "linear" thought process I have a "3 dimenisonal" thought process. I can see how point A connects to B. and take into account the thickness of the line that connects them. I cannont, however, see how a sentence will be inturpeted before i type it. nor can i remember a name 3 seconds after its been told to me.
 
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Old 04-06-07, 11:45 PM
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Yep, I know exactly what you mean!

But you PA. folks still talk "funny".
 
  #17  
Old 04-07-07, 12:39 AM
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not yet im still new to PA. I was livin in "JOISEY" for a long time and before that "NEW YAWK".. i still get the NY accent here and there. People around here say there O's weird. it has a "OW / OY" sound to it. instead of "come on" it "COMB OWYN"
 
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