Replacing electric cooktop 30A vs. 40A

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  #1  
Old 02-04-12, 06:42 AM
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Replacing electric cooktop 30A vs. 40A

The existing circuit is 30A. I'd like a cooktop that needs 40A. The existing SE cable is Aluminum 8 Gauge. The distance from the panel is 75 feet. My gut tells me this is too long for 40A can anyone tell me if I am right or wrong?

If it is too long can I run a 6 Gauge for the first 40 feet that I can easily access then use a junction box to connect the existing wire limiting the 8 gauge to 35 feet?
 
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Old 02-04-12, 07:47 AM
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The 2005 NEC reads as follows: “Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Parts I and II of Article 334, excluding 334.80.”

Since Part I of Article 334 for NM cable had absolutely nothing to do with SE cable, Part I was deleted in the first paragraph of 338.10(B)(4)(a) for the 2008 NEC. In the 2005 NEC, SE cable was required to comply with Part II of Article 334 with the exception of 334.80. In the 2005 NEC, this section required NM cable, but not SE cable, to comply with the following: “the ampacity shall be in accordance with the 60°C (140°F) conductor temperature rating. The 90°C (194°F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor.” By deleting “excluding 334.80” in the 2008 NEC, SE cable, where used as branch circuits or feeders, now must comply with the same ampacity rating as NM cable. This change was made for the 2008 NEC since SE cable often contains similar conductor insulation as NM cable, and where installed inside walls and in insulation, SE cable has heat dissipation similar to NM cable.

SE cable installed as branch circuit or feeder wiring in the interior of a building or structure is required to have an ampacity rating based on an insulation rating of a 60°C conductor and will reduce the allowable ampacity for the cable requiring a larger conductor based on the 2008 NEC. So in a nut shell, your now existing conductor is only good for 30 amps. But, depending on the year it was installed, you may be able to get an exception. Without the exception, you would have to run a new circuit. With an exception, you should be fine with the existing cable as is.
 

Last edited by SeaOn; 02-04-12 at 08:21 AM.
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Old 02-04-12, 08:20 AM
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Even if only one foot away you can't do it. Aluminum #8 is limited to 30 amps. You can run #8 copper the whole way or #6 aluminum. If the cook top is 240v only you can run 2 conductor cable. If it is 120/240v you must run 3 conductor cable.

Note: Seaon posted while I was typing. See his post above this one for a more complete explanation.
 
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Old 02-05-12, 06:09 AM
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Ray, SeaOn,
Thank you both for your reply and the detail. The house was built and cable run in 1978 and the cable does not run inside insulation it pokes through 8in of insultation only twice so it should disapate well. Any guess on odds for an exception? Should I bother for is 8 gauge AL suitable for 75 feet for 40A?
 
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Old 02-05-12, 06:53 AM
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I wouldn't bother or waste my time. Even if you could get an exception, is it worth taking the risk of a possible fire? Per Ray's last post, the #8 aluminum is only good for 30 amps.

Aluminum #8 is limited to 30 amps. You can run #8 copper the whole way or #6 aluminum.
My opinion is that I would want to get rid of the old aluminum branch circuit wiring anyway.
 
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Old 02-05-12, 07:20 AM
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While the problem with aluminum conductors was in the smaller branch circuit sizes, i would replace the run. Use #8 copper.
 
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Old 02-05-12, 12:53 PM
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I wouldn't bother or waste my time. Even if you could get an exception, is it worth taking the risk of a possible fire?
Casual, can you explain the above? Why you believe it would start a fire?? Just curious. Thanks!

Also, read my post below. Forget it, I’ll repost what I said here:
SE cable installed as branch circuit or feeder wiring in the interior of a building or structure is required to have an ampacity rating based on an insulation rating of a 60°C conductor and will reduce the allowable ampacity for the cable requiring a larger conductor based on the 2008 NEC. So in a nut shell, your now existing conductor is only good for 30 amps. But, depending on the year it was installed, you may be able to get an exception. Without the exception, you would have to run a new circuit. With an exception, you should be fine with the existing cable as is
 
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Old 02-05-12, 03:44 PM
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In my opinion, any time you increase the overcurrent protection on a circuit such as this even 10 amps beyond the conductors rated capacity you are taking a risk.
 
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Old 02-07-12, 11:36 AM
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In my opinion, any time you increase the overcurrent protection on a circuit such as this even 10 amps beyond the conductors rated capacity you are taking a risk.
I agree safety "Must" be a concern—as this is the reason code changes>>>to improve safety. But, if the OP’s install fail under the 2005 NEC, or if his or her jurisdiction are still using the 2005 NEC, would the OP then be required to run a new circuit?
 
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Old 02-07-12, 12:12 PM
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Just my opinion but one reason to DIY is to do it better then just minimal to get by. We now know there is a safety issue so why not bring it up to modern standards rather then cross your fingers and hope? But just my opinion.
 
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Old 02-07-12, 02:44 PM
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Just my opinion but one reason to DIY is to do it better then just minimal to get by. We now know there is a safety issue so why not bring it up to modern standards rather then cross your fingers and hope? But just my opinion.
An it’s a good one!!! I believe if they are doing it themselves, then they should not have any excuses to not do it above code—seeing that they “may have" saved money by not hiring a professional. On the other hand, doing it yourself could cost you more…..LOL.
Note: Knowing code can save a person or company money
 
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