Table 220.19

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royta

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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 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 some thin breakers. I'll have to look and check. If not, I want to use Table 220.19 and only use one circuit for both appliances.

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

[ September 03, 2004, 05:29 PM: Message edited by: royta ]
 
Re: Table 220.19

Your first calculation looks good, except I think a 40A ciruit is all that is needed. I don't understand why you increased the 9.6 kW to 12 kW? Note 2 doesn't apply for your question and can be calculated identical to the first calculation per Note 4. This would only require a 45A circuit and the same conductor sizes could be used as the first calculation.

Section 210.23(D) is not an issue for cooking equipment as they are not lighting outlets and I don't see how 422.11(A) is in conflict with 220.19?
 
Re: Table 220.19

Thank you very much. Could you please explain to me why Note 2 does not apply? I want to eliminate all future confusion. Thanks.

Roy
 
Re: Table 220.19

You are trying to determine the size of the branch-circuit load and not the demand load on the service or feeder. As stated, Note 4 applies and not Note 2.
 
Re: Table 220.19

OK, so basically Notes 1,2, and 3 only pertain to demand load. Note 4 pertains to branch circuit load.

When would I need to determine demand load?
 
Re: Table 220.19

Originally posted by royta:
OK, so basically Notes 1,2, and 3 only pertain to demand load. Note 4 pertains to branch circuit load.
Click to expand...
When would I need to determine demand load?
Click to expand...
:) I guess so you can take this demand factor along with the load requirements of the other items in the building, to see how large of service is necessary. Right?
 
Re: Table 220.19

Originally posted by bphgravity:
Your first calculation looks good, except I think a 40A ciruit is all that is needed. I don't understand why you increased the 9.6 kW to 12 kW? Note 2 doesn't apply for your question and can be calculated identical to the first calculation per Note 4. This would only require a 45A circuit and the same conductor sizes could be used as the first calculation.
Click to expand...
Originally posted by bphgravity:
You are trying to determine the size of the branch-circuit load and not the demand load on the service or feeder. As stated, Note 4 applies and not Note 2.
Click to expand...
Thank you bphgravity, I now understand the difference between the two Notes. I am a bit confused about the breaker needed though. In the first calculation, I have dertermined the load to be 40A. Why is it I can get away with a 40A breaker? 40A X 125% is 50A.

I'll do my second calculation again, but correct this time.

9.6kW + 7.2kW = 16.8kW
16.8kW - 12kW = 4.8kW = 5kW
5% X 5kW = 25%
.25 X 9.6kW = 2.4kW
9.6kW + 2.4kW = 12kW
12kW / 240V = 50A

How did you arrive at 45A?

Originally posted by bphgravity:
Section 210.23(D) is not an issue for cooking equipment as they are not lighting outlets and I don't see how 422.11(A) is in conflict with 220.19?
Click to expand...
I read Article 210.23(D) incorrectly. I seemed to have missed the "non" in "nonlighting".

Article 422.11(A) second sentence: "If a protective device rating is marked on an appliance, the branch-circuit overcurrent device rating shall not exceed the protective device rating marked on the appliance." By treating more than one appliance as a single appliance as in Note 4 of Table 220.19, you could actually end up using an overcurrent device that is rated higher than what the marked rating is on one of the appliances. Table 220.19 Note 4 must be an exception to 422.11(A).

I'm actually a bit nervous to utilize Table 220.19. The reason being, is that the marked rating of the just the wall oven alone is 40A. From the looks of the countertop ranges the customer is picking from, the range will also be right in there at 40A. So basically, two appliances with overcurrent ratings of 40A, will be supplied by a single 40A breaker. I certainly don't want to be called on Thanksgiving Day. I guess their alternative is for them to have me do a panel upgrade. I guess if the NEC allows for it, it's a good possiblity that I'll never get that phone call.

Thank you for your help.

Roy

[ September 04, 2004, 03:22 AM: Message edited by: royta ]
 
Re: Table 220.19

1. I don't feel there is any reason to increase the 40A by 125% as I don't consider cooking equipment a continuous load.

2. You second equation is wrong in that you increase the value of one range in Column C by 5% for every kW over 12. You increased 9.6 kW? You should have increased 8 kW by 25% resulting in only needing a 45A breaker.

I think the allowances of Table 220.19 provide a fairly efficient operation of cooking equipment in a dwelling. I feel that even though the nameplate of each piece of equipment is near or at the single OCD of both ranges, I think the chance of both appliances being used at full load together is not probably or even practical. Yes, holidays could present a possible problem, but I think you would be okay.
 
Re: Table 220.19

OK, I see it now. Row 1 of Column C tells me the maximum demand is 8kW. I increase the demand by the percentage, not the highest rated appliance rating.

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.

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

I was also wondering if I should increase the kW of each appliance to the next whole kW, but it looks like Note 1 explains this is not necessary. Why else would the note say, "...increased 5 percent for each additional kilowatt of rating or major fraction thereof by which the rating of the individual ranges exceeds 12kW."

Because Note 4 allows me to treat a specific combination of appliances as a single appliance, it is not necessary to change the math, even if one of the individual appliances is rated over 12kW. This is because Note 1 is referring to the single appliance (combination of appliances as allowed in Note 4). Correct?

I only use Notes 2 and 3 if I have a combination of appliances that does not fit under Note 4, correct? Examples would be the number of appliances, or the sum of the appliances added together was higher than 27kW. I can also use Notes 1, 2, and 3 for when I want to figure the demand factor for sizing the service supplying the panel that the appliances will be branched off of, correct?

Thanks again for your help.

[ September 04, 2004, 10:39 AM: Message edited by: royta ]
 
Re: Table 220.19

Regarding the use of the 40A circuit in my first example, is there a code specifying that I can not use a higher rated circuit, like a 50A? You're response of, "Yes, holidays could present a possible problem, but I think you would be okay" makes me want to make the jump up to a 50A. Afterall, there are plenty of houses wired for a single 50A circuit even though the customer might be using a gas appliance, or before the General, let alone the Electrician, knows which electric range a customer will be using. They might know the size, and that it is a built in or a free standing, but they might not know the specific kW just yet, because they are still choosing the specific model.

[ September 04, 2004, 10:45 AM: Message edited by: royta ]
 
Re: Table 220.19

I just found out the funniest dang thing this morning. The customer is installing a gas cooktop. Oh well, I'll just install a 6-3 w/ ground SE cable (Al) and put it on a 40A breaker.

Thanks for the help everybody.
 
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