Oven problems - part 2!!! Help!

OK - so I'm ready to put the wires in for the oven (forgetting for a moment whether or not it will be "wired in" or have a plug attached to the end of it. Just need to get the wall closed up!

So here's the problem. The oven is 120v/240v, and rated at 4.8kw.

The oven (a Kitchenaid built-in single convection oven) installation documentation says I need to use 8AWG wire!! I had already bought 10AWG, based on advice from this board and from my reading (all done before I received the actual oven).

So this 8AWG NM wire is *massive*. Ridiculous - I can't even fit it into a box to wire it!

I called Kitchenaid to verify the amperage (which, by my calculation, is 20A). The operator didn't have the amperage, but felt that "if my local codes permitted" I might be able to use 10AWG, based on the decal on the oven door (which had the 4.8kw rating).

Any thoughts? If I can get away with 10AWG then I can put this bad boy in tomorrow and be done with it. If I need to use 8AWG then it's going to be a *royal pain*. Shouldn't 10AWG handle 30A?

Help!

Thanks,

Tony

 

your 4.8kw stove will draw 40 amps. on a 120v. circuit, and 20 amps. on a 240v. circuit. #12 AWG is good for 20 amps., #10 AWG is good for 30 amps, and #8 AWG is good for 40 amps. are you going to be using 120v, or 240v to power your stove?

hope this helps!..

ps:--->formula for calculating current draw is "KW x 1000/ voltage"

 

Technically, you must follow the manufacturers instructions. Although if this was an older unit, and had no instructions, 4.8kW @ 240V is 20A which would use a 30A circuit breaker and #10AWG.

 

Wait A Minute!!!

You said that the installation instructions told you to use a #8 AWG to wire this unit. If that is correct then you MUST wire the unit with #8! To use anything else could possibly void your warranty and would make the UL Listing of the product Null and Void.

When you are wiring an oven it's not as simple as it sounds. Meaning the 120/240 volt issue. Because of the fact that you will have both series and parallel connections during use. At times you will be using only 120 and at times you will be using 240.

If the installation instructions detail #8 you're gonna have to bite the bullet. 110-3 (b) Installation and use: Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

Sorry

 

But here's what's strange: the wire coming out of the oven cable conduit is 12AWG - which matches the 20A rating that you get from the 4.8kw @ 240v!

 

...And the KitchenAid website says:

Electrical Requirements:
208/240 volt, 60 Hz., 30 amp, grounded, separate circuit required. Fuse both sides of the line. A time delay fuse or circuit breaker is recommended.

This seems to tell me that I can do 10AWG.

Tony

 

Seems that you have a dillema here! The code says that you have to go by the installation instructions!!

As for the wire coming out of the unit being a #12, this is common and it means nothing to us. The same is true of the power company when they hook you up. The line that they use to supply power to your home is much smaller than the wire coming from the weatherhead for several reasons.

The manufacturers are allowed to do this because they have the unit tested and listed by UL. As long as the unit is not altered from the UL listing that wire coming out of the back is as it should be.

My only suggestion would be to contact the manufacturer and talk to a technical service rep and get their answer. Be cautious here, if they tell you that you can use the #10 make them send you something in writing that says this. This is what we as contractors are forced to do all of the time.

In this trade, if you do something contrary to installation instructions you have to have the documentation to back it up!

Good Luck!!

 

Technically Speaking!! To address the issue of the 4.8KW rating and the 20 amps. If you calculate this right the 4.8 rating will give you 20 amps that part is correct. However, this circuit has got to be rated at 125% of the load!!

If you do the math that shows a load of 25 amps. Since the maximum overcurrent protection allowed on a #10 is 30 amps and 80% of that is 24 amps, technically, you can't put this load on a #10 wire. You would have to go to the next higher size of conductor and that would be the # 8 that the installation instructions call for.

Got to be a #8

 

If you didn't have manuf. instructions:
The load is 20A. You size the wire and breaker @ 125% so 30A breaker with #10 wire.
Not 125% on top of 125%.

 

Ron,

You're exceeding the limits of the conductor!!! The load must be 80% of the allowable conductor ampacity since this would be considered a continuous load. I am not double-derating here. I was pointing out that if you use the #10 you will exceed the allowable load since the maximum overcurrent for that conductor is a 30 amp breaker.

That is why the manufacturer calls for the #8 wire.

Irregardless of that fact, the code also says that you must install that unit according to the installation instructions that are provided with the unit and they call for a #8.

 

I've never heard of an oven being considered a continuous load by a AHJ. Yes, it's possible for an oven to be on for three house, but just because it's possible does not mean that it meets the criteria for a continuous load.

 

John,

Locally, they consider the oven to be a continuous duty load. That is why I mentioned what I did. Not sure where you or the poster are located, I know that things are done differently in different parts of the country and this is one of ours.

 

I'm located in Los Angeles, CA.

The KitchenAid website says:

208/240 volt, 60 Hz., 30 amp, grounded, separate circuit required. Fuse both sides of the line. A time delay fuse or circuit breaker is recommended.

This seems to indicate to me that I can run #10AWG.

Tony

 

Print the information from the website out and keep it with your papers. Install the 10 awg and happy cooking!! If it was me, I would run the 8 and use a 2 gang box. Problem solved.
Brian

 

You are essentially double derating,,, but anyway,, if the run was short,,, under 50 foot or so 10 would be fine,,, Even if the thing was wide open,, which it isnt most of the time,, Personally I wouldnt lose sleep with it on a 10.

 

Sparksone42: You quote 110.3(B) (any instructions included in the listing and labeling). These instructions would have to come from an organization meeting the definition of Listed in the NEC. "The Manufacture" of the product would meet this qualification. So, if the manufacture was requiring #8, then I have to agree with you, and this installation would have to meet this standard, regardless of the name plate rating.
If this equipment was bought used then UL standard 1082 would have to be referred to. From there the UL listing is still going to refer you back to the manufacture for instructions, if none exist (Company out of business) then the name plate could apply.
If the nameplate was to apply then 220.3(C)(1)(2) is were we would start at to determine the branch circuit rating. This takes us to 220.3(B)(2). From here we end up at 220.19 note 4, “Branch circuit load”. (One wall mounted oven shall be the nameplate reading of the oven.)
This Oven is rated at 4.8kw 120/240.
210.19(A)(3) states branch circuit conductors shall have a rating not less than the load served.
The 4800kw is divided by 120 = 40 amps. The ressone being is both 120 and 240volts are being utilized in the circuitry of the oven, at the same time.
Where two tabulations are calculated exist the worst of the two apply.
40amps, not 20amps
310.16, #8 good for 40amps at 60’C NM-B.
210.20© Equipment, gives us the overcurrent protection device. This intern takes us to 240.3.
240.3 Other Articles: “Appliances” 422
422.11(A) Shall not exceed the appliance rating.
240.4---40amp breaker.
Looks like #8 to me guys.

 

Why would you suggest installing a 40-amp breaker when the manufacturer's installation instructions tell you to use a 30-amp breaker? Surely it cannot be right to disobey the manufacturer's instructions.

 

Read my post it states to wire the unit by the manufacture instructions. (if no instructions exist then)...

 

Sorry, I missed that. We do get off on tangents here. There is a real danger, however, that the original poster may interpret a piece of advice as aimed at him. I'm not sure the best way to mitigate that danger.

 

Thank you, Aphares. You took the time to go through and list the relavent code articles.

The one question that I have in regard to this unit is whether or not it is actually just an oven or is it a range. I forgot to ask this in the beginning as I was just assuming that it was in fact an oven. I know that many people call a range an oven and for the purposes of applying the correct code articles there is a difference.

I agree with all of Aphares calculations and code references unless the poster tells us that this unit is a range, as in a drop in range. If this were a range then note 4 would tell us that we would use Table 220-19 and not the nameplate.

If this is indeed a range then it would mean that you could use the derating factor of 80% and this would make it so that the #10 could be used.

Any thoughts?

 

A question,,, and have seen it before. It really seems like the name plate rating would apply as I have seen instructions that were kind of generic and applied to a couple of models?? They just cover their ass by giving the heaviest wire,,, as their website indicated it was acceptable to use 10 for this app. Second, aphares says the worst of the conditions applied according to the code,, so if the actual is 4.8 and 40 A on 120 where is the 80% saftey,,, or the 125% conductor rating of the load? So 8 wire must be used even if at 240???? just in case it gets hooked to 120?? Which in case there is no reserve.

 

sberry,

You're right the nameplate rating will apply as apares stated in his reply. There are two problems though.

One is the fact that you have to satisfy 110-3(b), which says that you have to go by the directions supplied with the unit itself. Thp said that the instructions called for a #8, so be it.

Second, I posed a question just above yours relative to semantics. Thp is calling it an oven and we are applying the code based on that fact. However, some people call a range an oven and the code delineates the two. Like aphares said, since this is a branch circuit we apply note 4 of 220-19. If it is an oven as the code defines an oven which is just a cooking chamber with no burners on top then the nameplate rating applies. If this unit is a range then the code says that you refer to table 220-19 and this unit will fit into the 3 1/2 - 8 3/4 kw column, which at one appliance gives an 80% derating factor.

As for the 120/240 issue, it's been awhile but, on oven, range, what have you, is wired both in series and parallel through the controls. That is why aphares is saying that you have to use the worst case scenario of 120 volts. I am not sure that I agree that you would draw 4.8kw using the 120 volts though.

Maybe this is an issue that we should also post on the electric appliances heading and ask one of those "techs" to answer.

 

Does the installation manual say to USE #8 or does it reccomend the use of #8. There is a difference. A reccommnedation is not a requirement.

 

4.8 kw rating for even a single oven seems awfully low. YOu would calculate with the voltage supplied to the oven which is 240 volts.

Normally the only 120 volt usage is timers, clocks and light bulb in a range.

You calculate the rating of this oven in amps by dividing the 4.8 kw = 4800 volt amps divided by 240 volts = 20 amps.

Sizing the branch circuit is controlled by 210.19 copied below;

COPIED SECTION OF 2002 NEC;

210.19 Conductors — Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts.
(3) Household Ranges and Cooking Appliances. Branch-circuit conductors supplying household ranges, wall-mounted ovens, counter-mounted cooking units, and other household cooking appliances shall have an ampacity not less than the rating of the branch circuit and not less than the maximum load to be served. For ranges of 83/4 kW or more rating, the minimum branch-circuit rating shall be 40 amperes.

COMMENTARY;
Notice the minimum branch circuit rating shall be 40 amps but only if the appliance is a range and only if that range was rated at 8 3/4 kw or more.

This rule of 40 amps would not apply to this oven being rated at 4.8 kw.

The rule in 210.19 states the branch circuit must be not less than the rating of the rating of the oven.

PLEASE CONFIRM THAT YOUR ARE READING THE CORRECT AMP RATING FOR THE COMPLETE OVEN AND NOT JUST A SINGLE ELEMENT.

Now lets think on this a bit. Most oven heat elements are 4500 watts. A single oven will use the top element during broil mode or the bottom element for the bake mode of that oven. The clock and light bulb would be almost unnoticable on the load of the oven. The 4.8 kw may very well be right but check to make sure.

4.8 kw computes at 240 volts to be 20 amp. In dwellings you do not use the 25% increase for continuous load because inside a dwelling is not considered as continuous duty except for motors.

The load is right on the 20 amps maximum with no give. This would call for a 10 awg copper 30 amp rated branch circuit per the NEC.

Those that use 220.19 table is incorrect in sizing the branch circuit as can be seen in 210.19. Table 220.19 is now used for demand load of more than one range or oven on the same branch circuit but a single oven or range must be ruled by 210.19 at 100% load in a dwelling for noncontinuous load.

Those that said that 110.3.B applies are correct. The manufacturer's instructions must be followed. It is a good possibility that the manufacturer is suggesting the 40 amp rated wire or is calling for 8 awg aluminum or 10 awg copper. I am suspecting something is being read wrong in those instructions.

Recheck what is truly being said in those manufacturer's instructions. Make sure that it does not say minimum branch circuit size is 10 awg copper or 8 awg aluminum.

Just curious and would like to see what it actually says for sure.

Hope the above helps

Wg

 

"Those that use 220.19 table is incorrect in sizing the branch circuit as can be seen in 210.19. Table 220.19 is now used for demand load of more than one range or oven on the same branch circuit but a single oven or range must be ruled by 210.19 at 100% load in a dwelling for noncontinuous load." (wg)

220.4(C)
(C) Range Loads. It shall be permissible to apply demand factors for range loads in accordance with Table 220.19, ((including Note 4.))

Note 4 apply's to the branch circuit, and appling the demand for one range is allowed, but not for one oven.

 

Table this,, table that, instructions this or that,,, if the dam thing pulls 20 A them makes big time sense that it will run on a 30,,,, ,,, man,, you think we going to the moon!!!!!!!!!!!!!! Sometimes we can over brain it just a bit.

 

WG

This is one time that I am going to have to disagree with you. Table 220-19 Note 4: Specifically states that you can size the branch-circuit load for one range in accordance with table 220-19

 

Spark142, I have no problem with anyone disagreeing with me. Often times I run with foot in mouth desease. Aphares is along with you in stating that 220.19 note 4 is allowed to be used to size a branch circuit serving a range.

Aphares pointed out that this note 4 does not include an oven.

My understanding is that this post relates to an oven and not a range.

Considering that one burner of a range would push the stated 4.8 kw rating stated in this post I really don't believe this post to be relating to a range but only to an oven which would not be allowed to be used concering 220.19.note 4 concerning an oven.

I believe also if you check 210.19 the last part of that rule coinsides with the sizing of a normal range in 220.19 using note 4.

Confusing at times concerning the NEC. Wish the wording were less ambiguous concerning NEC rules. Would make life easier but maybe boring then being too easy no longer a challenge. Ain't it great the wording in the NEC not only gives us a challenge understanding what they are saying but helps us maintain our high blood pressure too.

Wg