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#89130 09/03/04 06:13 PM
Joined: Sep 2004
Posts: 138
R
royta Offline OP
Member
I have a customer who is having their kitchen remodeled. They will be using a wall mounted oven, and a counter top range - two seperate appliances.

I'm not sure exactly which range the customer is buying, but I do know that four out of ten they are more than likely considering are above 8.75kW (9.6kW, 8.8kW, 9.6kW, 9.6kW).

The oven the customer is buying is a GE Profile JT955 - 7.2kW

The house is not currently wired for electrical cooking appliances in the kitchen. The panel only has room for one 2-pole breaker, however, I may be able to put in a quad. I'll have to look and check. If not, I want to use Table 220.19 and only use one circuit for both appliances. Actually, even if I could use a quad, I think 220.19 would be best for the customer (cheaper).

I'll do two calculations utilizing Table 220.19, one with an 8.75kW range, and one with a 9.6kW range.

---8.75kW---
7.2kW + 8.75kW = 15.95kW
15.95kW - 12kW = 3.95kW = 4kW
5% X 4kW = 20%
.20 X 8kW = 1.6kW
8kW + 1.6kW = 9.6kW
9.6kW / 240V = 40A

Are my formulas correct? If so, according to Table 220.19, I can use a single 50A circuit to supply both appliances.

Table 310.16 says 8-3 SE cable (75 degrees C) or 6-3 NM cable (60 degrees C - Article 334.80) would work for a 50A circuit.

---9.6kW---
12kW (because 9.6kW is over 8.75kW) + 7.2kW = 19.2kW
19.2kW - 12kW = 7.2kW
5% X 7.2kW = 36%
.36 X 8kW = 2.88kW
2.88kW + 8kW = 10.88kW = 10.9kW
10.9kW / 240V = 45.41A

Can I use a 50A circuit, or do I need to go to a 60A circuit. 45.41A is 91% of a 50A circuit. If a 60A, then I need to use 6-3 SE cable or 4-3 NM cable.

Can I even use a 60A circuit for appliances? Look at Article 422.10(B). This refers you to Article 210.23. Article 210.23(D) is what scares me.

I know that according to the last sentence of Article 422.10(A) that you can use Table 220.19 if you'd like, but it seems that Article 220.19 and Article 422.11(A) contradict each other.

Anyway, could you please look this over and tell me I'm fine? I don't mind doing a panel upgrade if necessary, but if I can help out the customer and save them some time and money, I'd like to.

Thanks.

-Roy

2017 / 2014 NEC & Related Books and Study Guides
#89131 09/04/04 02:01 AM
Joined: Jul 2004
Posts: 9,667
Likes: 5
G
Member
I think you could get away with putting both on a single 50 but I would put in 2 circuits, just so I don't get a call on Thanksgiving wanting to know why the breaker tripped.
Just about the time I really start believing nobody would be using all the burners and the oven at the same time, I walk in the kitchen and see my mother in law doing it.
I believe the installation instructions limit you to 50a. That is dictated by the internal wiring.


Greg Fretwell
#89132 09/04/04 04:02 AM
Joined: May 2003
Posts: 2,876
E
e57 Offline
Member
Calculation looks ok, but yeah, expect a call on turkey day and X-mas!

Also, why not do them a favor by up-grading the service. Two spots left you're going to fill.... They're gonna have to do it sooner than later. Don't know the service size, but X-mas could be a main trip. Both units and every light, plus some, on in the house. Who knows what else... Not to mention they may whan to add a 120v 15A, "Well sorry, you need a new panel for that..." Do the new panel now, and save the hassle of pulling out your own work for this stuff, to do it later.

Or, if the service is beefy enough, do it on a sub.....


Mark Heller
"Well - I oughta....." -Jackie Gleason
#89133 09/04/04 10:38 AM
Joined: Sep 2004
Posts: 138
R
royta Offline OP
Member
Actually, my second calculation is wrong.

Correct calculation is as follows:
9.6kW + 7.2kW = 16.8kW
16.8kW - 12kW = 4.8kW = 5kW (Note 1 says to round up, right?)
5% X 5kW = 25%
.25 X 8kW (from Row 1, Column C) = 2kW
8kW + 2kW = 10kW
10kW / 240V = 41.7kW

What's happening, is that I'm getting confused by the example on p.109 of the '02 NEC Handbook. It lists the three appliances' kW ratings: 8kW, 7kW, and 6kW. Because the equation uses 8kW and the highest individual appliance is also rated at 8kW, I incorrectly used the highest rated appliance (9.6kW) for my math. The Handbook example would make more sense if the highest rated appliance was 10kW.

#89134 09/04/04 12:38 PM
Joined: Jul 2004
Posts: 9,667
Likes: 5
G
Member
These 220 calcs are good for computing the average load on the service since we assume diversity but when these all end up on a single branch you are looking at the instant load at any particular time.
What you *can* do may not translate to what you *should* do.


Greg Fretwell
#89135 09/09/04 07:36 PM
Joined: Sep 2004
Posts: 138
R
royta Offline OP
Member
It turned out that the homeowner is installing a gas cooktop, not an electric cooktop like I originally thought.


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