Residential Cooktop and double oven Compliant? Practical?

[flatlander]

I would like you all to weigh in I was recently asked if the following was compliant and or practical. I personally think it is compliant but not practical.
This is a remodel situation. Can you take the existing Range Feeder 6-3 w.ground and terminate it to a new Sub panel then feed two circuits one 40 amp to a 7.9 Kw cooktop and a 6.75 KW double oven.
I calculate as : 14.65 KW
subtract 12 KW from 14.65 = 2.650
2650 X 5% = 2782.5
8kw the min demand plus the amount over 12KW

8000 + 2782.5 = 10782.5
10782.5/ 240

44.93 amps

it looks ok but i feel it is impractical as this home owner entertains a lot. It will be difficult to run a new circuit as this is a condo and another unit below and concrete floor.
What do any of you think.

 

[jwelectric]

see 210.19(A)(3) Exception

 

[flatlander]

That really does not answer my question.

 

[jwelectric]

Why would one want to spend money to install a remote panel when there is no need?
Yes what you purpose is compliant as long as there is four conductors in the branch circuit but it sure is a waste of money

I calculate as : 14.65 KW
subtract 12 KW from 14.65 = 2.650
2650 X 5% = 2782.5
On this line it would be 2.65 rounded up to 3 times 5% = 15%

8kw the min demand plus the amount over 12KW

8000 + 2782.5 = 10782.5
Here it would be 8000 * 115% = 9200

10782.5/ 240

Then 9200/240 = 38.3 amps

not 44.93 amps

 

[suemarkp]

Also, can't you use the kitchen cooking tap rule to just run taps off this 6-3 circuit to feed the oven and cooktop - no subpanel required? Or is this already a feeder with a panel and multiple kitchen circuits?

I think you have enough margin to run this reliably. Even if everything is on, these elements cycle on and off. Perhaps the circuit could trip if both ovens are preheated at the same time and all 4 cooktop units are turned up full at the same time. But a 50A breaker will allow a 10% overload for quite some time and a 20% overload probably 10 minutes or so. You may even be able to bump the brreaker to 60A as long as the feeder calculates to 55A or less.

 

[flatlander]

Why would one want to spend money to install a remote panel when there is no need?
Yes what you purpose is compliant as long as there is four conductors in the branch circuit but it sure is a waste of money

I calculate as : 14.65 KW
subtract 12 KW from 14.65 = 2.650
2650 X 5% = 2782.5
On this line it would be 2.65 rounded up to 3 times 5% = 15%

8kw the min demand plus the amount over 12KW

8000 + 2782.5 = 10782.5
Here it would be 8000 * 115% = 9200

10782.5/ 240

Then 9200/240 = 38.3 amps

not 44.93 amps

Thanks but Huh!

Which is it.
I don't see how you just add 15% to the basic 8KW and get the final number?

 

[Smart $]

Thanks but Huh!

Which is it.
I don't see how you just add 15% to the basic 8KW and get the final number?

Table 220.55...

Notes:
1. Over 12 kW through 27 kW ranges all of same rating. For ranges individually rated more than 12 kW but not more than 27 kW, the maximum demand in Column C shall be increased 5 percent for each additional kilowatt of rating or major fraction thereof by which the rating of individual ranges exceeds 12 kW.

As an aside, I always had a smidge of doubt on application of Notes 1 and 2... in that when these say ranges, does it include other cooking appliances or just ranges???

 

[Smart $]

Another aside...

Why do Notes 1 and 2 cap the ranges' ratings at 27kW? AFAIK, there is no limitation to a range's rating in the NEC. Is there some other standard that limits a range's rating to 27kW... and if so, what law stipulates the standard must be adhered to.

And then there's the question (purely theoretical) on what do we calculate if a range is rated over 27kW?

 

[HEYDOG]

Just my opinion. I say when you get over 27 kw I doubt that you would be dealing with a
residential cooking unit but most likely a commercial cooking unit.

 

[suemarkp]

Thanks but Huh!
I don't see how you just add 15% to the basic 8KW and get the final number?

The baseline is 12KW. For that, you use an 8KW load value. For each KW above 12KW, you increase the 8KW by 5%. So 14.6 KW is 2.6 KW above 12KW. You round this up to 3KW. At 5% for KW, that is a 15% increase. 8 KW * 1.15% = 9.2KW.

Note 4 to the table says: Branch-Circuit Load. It shall be permissible to calculate the branch-circuit load for one range in accordance with Table 220.55. The branch circuit load for one wall-mounted oven or one counter-mounted cooking unit shall be the nameplate rating of the appliance. The branch-circuit load for a counter-mounted cooking unit and not more than two wall-mounted ovens, all supplied from a single branch circuit and located in the same room, shall be calculated by adding the nameplate rating of the individual appliances and treating this total as equivalent to one range.

 

[kwired]

Nothing wrong with connecting the new appliances both to the existing circuit with no additional overcurrent devices.

You can try to justify any calculations if you want, but there is very little chance of overloading long enough to trip the overcurrent device and this is done quite frequently.

 

[flatlander]

Ok great help. I now see how they do it.
The parting thing I'd like to see feed back on is , I know it will be code compliant to put all this on the same circuit. But what happens when you are entertaining a great deal cooking for a large family. I can see a lot of use. Is this a practical solution. I have always used separate branch circuits for each appliance and never seen this done this way although compliant.

 

[kwired]

But what happens when you are entertaining a great deal cooking for a large family.

What happens if you connect a 14.65 kW range to a 50 amp circuit and cook the same meal?

 

[Little Bill]

Ok great help. I now see how they do it.
The parting thing I'd like to see feed back on is , I know it will be code compliant to put all this on the same circuit. But what happens when you are entertaining a great deal cooking for a large family. I can see a lot of use. Is this a practical solution. I have always used separate branch circuits for each appliance and never seen this done this way although compliant.

Since the appliances cycle on/off, I doubt it will overload the breaker. It may go over the breaker rating on occasion, but as has been said, it would have to remain that way for a period of time to trip the breaker.

I think that is still cheaper/more efficient to leave them on one circuit, and if it trips occasionally the HO would have to try and limit the loads somewhat.
Only way to know for sure is for them to try it!

 

[kwired]

14.6 kW is 61 amps. How long will a 50 amp breaker hold at 61? That is 122% of 50 amp rating.

How long will all heating elements remain on with no cycling?

Most of the popular smooth top cooktops will not remain continuously on like the older exposed element types as it may overheat the glass top and crack it. Ovens only take maybe 5 minutes to preheat then they will cycle off until more heat is needed.

Your best chance of tripping a breaker is if you turned every heat element on its highest setting all at same time, but I don't think the chance of all them drawing continuous full current long enough to trip the breaker is all that great.

Just looked at the range in my house. It is 13.5 kW. That would be about 56 amps, and it is only on a 40 amp breaker. That would be 140% of the 40 amp breaker. Been several times when all cooktop elements were running as well as oven and have never had the breaker trip.

 

[HEYDOG]

The other thing that I would look at is if the manufacturer specifies these to be on dedicated
circuits. If they do and you put them on the same circuit it would then be a code violation as well as possibly void any warranty.

 

[kwired]

The other thing that I would look at is if the manufacturer specifies these to be on dedicated
circuits. If they do and you put them on the same circuit it would then be a code violation as well as possibly void any warranty.

Though I agree it would be a misapplication of instructions, I strongly question what kind of damage may occur that should void any warranty.

 

[HEYDOG]

Just my opinion but I would think not following manufacturers instructions would be enough to
void the warranty. Not saying that I could see it being a particular issue. I would also think that if it has a UL
listing that it would have been tested and listed to be on a dedicated circuit if that is what the instructions state.

 

[flatlander]

Thanks all,
I have heard so many variants of this over the years.
All the companies I have worked for always pulled a separate BC for each cooking appliance. There seems to be always a new way to skin a cat so to speak.

 

[EV607797]

I can say with certainty that I've seen probably hundreds of range/oven installations on a single BC using the tap rule in Virginia and North Carolina over my years in the industry. Granted, most of them were done in the 60s and 70s, but they obviously have stood the test of time. On a recent kitchen remodel that I did, we had to run a new circuit for the oven due to the KW rating of it. We just reused the 50 amp circuit using SEU cable for the cooktop. This worked out perfectly (and legally) since the induction cooktop didn't require a neutral.