Can 13.9kw max load be powered by 50A circuit?

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  #1  
Old 08-01-04, 01:24 AM
mnmlemley
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Question Can 13.9kw max load be powered by 50A circuit?

I am remodeling my kitchen, replacing the range with a cooktop and double wall oven. The range was powered by 50A circuit. Can the same circuit be used for the cooktop and doulbe wall oven? Max pwr for both is13.9kW.

Matt
 
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  #2  
Old 08-01-04, 12:30 PM
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I would say no. According to my calculations, the double oven would pull approximately 58A. What does the documentation that came with the unit say about the required circuit?
 
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Old 08-01-04, 01:33 PM
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Cooking appliances do not live in the simple universe that allows you to divide watts by volts to get amps. It's been a while since I review these codes, so I can't say for sure, but wiring both a cooktop and an oven to the same 50-amp circuit is almost always permitted. I hope somebody who knows the details can post here and educate us all.
 
  #4  
Old 08-01-04, 03:22 PM
CSelectric
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I presume that both of these appliances are located in the same room, thus allowing us to apply NEC Art. 220.19

the combined load of the two appliances is 13.9KW, thus forcing us to calculate based on column C of table 220.19 (I'm including this data for the benefit of John and others with a code book handy.)

2 appliances with a combined rating of 12kw or less comes up as 11kw demand factor in column c.

According to note #1 the demand factor has to be increased by 5% for each KW over 12

so, 13.9kw is 2kw greater than the 12kw limit, therefore our demand factor must increase by 10%

11kw + an additional 10% = 12.1KW

Finally, 12.1 kw / 240V = 50.42 Amps

To be totally code compliant, you would need a 60 amp breaker and #6 wire.
 
  #5  
Old 08-01-04, 04:29 PM
Rlfrazee
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Actually I believe you will be well within code compliance with your 50 amp circuit. This requires application of note 4 and then note 1 of 220.19. Note 4 tells us that the branch circuit load for a counter mounted cook top and not more than 2 wall mounted ovens, all supplied from a single branch circuit and located in the same room, shall be computed by adding the nameplate rating of each individual appliance and treating this total to the equivalent of one range. In this case the total nameplate ratings add up to 13.9 Kw. Now we apply note 1 for ranges from 12 KW to 27 KW. We have one range the demand load for one range is 8000 watts (remember we are now working off note 1). Note 1 now says we increase the demand factor of column A by 5% for each Kw over 12 Kw or major fraction thereof. So we are 1.9 Kw over 12Kw. So 8000 watts demand factor in column A is increased by 760 watts. 8000 x 5% equals 400 watts per kw over 12Kw. 400 watts x 1.9 equals 760 watts. 8760/240 equals 36.5 amps.

A fifty amp circuit is fine but must reduce to 40 amp breaker keeping the #6 awg wire of the 50 amp circuit.
Must also be careful about neutral requirements in the new installation (i.e. the cook top commonly doesnt need the neutral but the oven does)
Must also double check wire size in current installation since you are wanting to serve two appliances from one branch circuit (i.e. cook top and double wall oven) so appliance tap rules will apply. Needing #6 awg to allow dual purpose branch circuit.........RL
 

Last edited by Rlfrazee; 08-01-04 at 04:48 PM.
  #6  
Old 08-01-04, 04:37 PM
CSelectric
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RL, you are correct in applying note #4, which changes the calculations to a base of 8KW. However, the calc would actually be 10% (5% for each KW over 12) of the base load factor of 8kw.

8kw + (8kw * .1) = 8800W
8800/ 240 = 36.67A

In this case it doesn't make a huge difference, as it still adds up to a 40A breaker.

In any case, thanks for catching my omission of note 4, that certainly makes a big difference in the calcs.
 
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Old 08-01-04, 05:12 PM
Rlfrazee
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No problem and yes should have been 8800 watts....RL
 
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Old 08-01-04, 05:14 PM
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Thanks guys. Really cool information.
 
  #9  
Old 08-01-04, 06:16 PM
CSelectric
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If you want to dig further into it John, gey ahold of the last 3 or four back issues of EC magazine. They've been doing a rather informative code focus on exactly this subject.
 
  #10  
Old 08-05-04, 02:31 AM
Snape
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Do you guys apply diversity factors when working out the correct ampage for breakers used with such appliances as cookers, water heaters etc...

For those who are not compliant with diversity it is basically based on the fact that with a cooker it is totally inlikely that all hobs on the cooker and over will be at maximum demand all the time.

Cheesr
 
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Old 08-05-04, 10:26 AM
Rlfrazee
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Yes Snape, calculations for cooking units are based to a large degree that not all heating elements will be at maximum all the time. Water heaters are treated according to their name plate rating.....RL
 

Last edited by Rlfrazee; 08-05-04 at 04:00 PM.
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Old 08-05-04, 11:06 AM
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Rlfrazee,

Could you explain why a 40A breaker would be required? I understand that the various load diversity factors would permit a 40A circuit to be used for this range, but if the conductor ampacity is 50A, then why couldn't a 50A breaker be used?

-Jon
 
  #13  
Old 08-05-04, 03:48 PM
Rlfrazee
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Yes. it would at first appear you could do this, however you are not protecting the wire but the utilized equipment (i.e. cook top and double oven) the wire must be sized to the branch circuit load. In this case you are also serving two cooking appliances from one branch circuit thus the requirement for 6 awg in order to meet dual purpose appliance branch circuit. If you put in a 50 amp breaker but only use one cooking appliance, say the cook top, and lets say it is nameplate rated at 6.7 Kw or 28 amps. Then for some reason an overcurrent occurs, the breaker will allow 22 amps over the maximum rating of the stove to flow before the breaker trips. Or it may trip due to heat, most likely current, but the heat will be allowed to exceed the listed rating of the stove at 50 amps. Either way the stove gets fried instead of protected. The catch here is you still have to have a big enough breaker to allow both appliances to operate normally on one branch circuit. So diversity is considered and most importantly safety. The 40 amp dbl. breaker is the result to achieve minimum saftey requirements. To improve the saftey would be to go down in breaker size not up. Simply put the wire would be fine (since it is 60 amp rated) but your $$$$ in appliances would not in the event of an electrical fault. Hope this helps .....RL
 

Last edited by Rlfrazee; 08-05-04 at 06:54 PM.
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Old 08-05-04, 04:07 PM
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Thanks, I am not the original poster, but was simply curious. It isn't simply the ability to use the existing 50A breaker, but also the ability to use all of the heating elements if one so desired, diversity be damned Load diversity is _not_ a requirement, but instead permission to go to smaller conductors and OCPD than the raw total of the connected loads.

I see your point about using the breaker to protect the individual appliances tapped off this circuit. The smaller the circuit breaker, the lower the power delivered to a potential overload fault.

In the ideal case, one might convert this range circuit into a feeder to a small subpanel, and then give each appliance its own OCPD, properly rated for that individual appliance. Without this approach, each appliance must be properly protected by the (big) breaker on feeding both appliances.

However prior to switching out to the 40A breaker, I would suggest looking at the instructions (including the nameplate) which came with the ranges and ovens. They may very well be properly listed to be placed on a 50A circuit.

-Jon
 
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Old 08-05-04, 04:44 PM
Rlfrazee
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Sorry Winnie for mistaking you for original poster...my mistake. I'm not exactly sure I'm following you on the diversity statement are you saying it isnt necessary to follow 220.19? You should be able to operate these units normally, all burners and oven elements just not everything on "HI" setting. Anyway I agree two individual circuits thru a subpanel would be an excellent way to serve these appliances. Whats your thoughts though about these units individually being rated for 50 amps? I agree that you most definitely need to read the electrical requirements for these appliances. The poster gave me the impression he had done so. Wondering though if both appliances together are 13.9Kw, as poster states, if you were to consider them individually that both would have 50 amp ratings. I believe I have seen "ranges" nameplate rated at 12.5 Kw with 50 amp ratings. When I go into supply houses sometimes I hear , "oh its a range circuit we put them on 50 amp breakers and 6 awg around here." Well there are ranges, there are cook tops,and there are ovens all very diverse in their power requirements. Was trying to give the poster a well accepted method for calculating his situation. There may very well be other methods but my learning has always been 220.19. Your points are well taken.....RL

Winnie: I edited the first reply to your question to remove the statements that reflected you were the original poster.
 

Last edited by Rlfrazee; 08-05-04 at 09:57 PM.
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Old 08-05-04, 09:57 PM
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What I am saying is that 220.19 points to a reduced minimum ampacity for branch circuits and feeders supplying household electric cookers. There is no requirement that you reduce the capacity of the feeders in this fashion; feeders can be as oversized as you wish, as long as you also meet the requirements for protecting the equipment served, and as long as your overcurrent protective devices can tolerate the available short circuit current.

-Jon
 
  #17  
Old 08-06-04, 08:56 PM
CSelectric
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Snape, diversity factor is a non issue in residential cooking appliances, as 220.19 already assumes a certain diversity factor. Commercial cooking equipment is, of course, a different animal all together. Of course, trying to slide by on diversity factor in a commercial kitchen is a service call waiting to happen, as you are dealing with cooking appliances that will very likely run at near 100% load for long durations.
 
  #18  
Old 08-08-04, 07:57 PM
Rlfrazee
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Winnie I see your point about diversity not a requirement.Though I do think it becomes more of an issue when serving two cooking appliances from one branch circuit instead of individual branch circuits...anyway great learning from you...RL
 
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Old 02-05-09, 05:50 PM
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hi guys just a pointer? your calulations for curent ratings, the supply voltage you are using is 240v. remember it droped to 230v so thats over a 2 amp increase on load.instead of 50.42amps it would be 52.60amps.
 
  #20  
Old 02-05-09, 06:59 PM
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This thread is almost 5 years old. Hopefully the OP has worked it out by now.
Andy
 
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Old 02-05-09, 07:50 PM
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Yeah...But what a great read!!!
 
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