Replacing Alum Wire on Electric Range

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  #1  
Old 05-26-04, 02:02 PM
Tom Lauer
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Thumbs up Replacing Alum Wire on Electric Range

I want to replace the existing aluminum wire circuit on my electric range.

The range is a Kenmore rated at 120/208, 9,5KW or 120/240, 12.6KW.

The range manufacturer recommends a minimum circuit of #8 copper wire on a 40 amp breaker.

Local power provider supplies 120/240 @ 80% power.

The existing aluminum wire circuit is connected to a 40 amp breaker.

The run from the breaker box to the stove is 28 feet.

I don't know if the range is three wire or four wire configuration.

Question(s):

1. Is a #8 copper wire, 40 amp circuit sufficient for the range? If I divide the 12.6 KW watts by 240, I get 52.5 amps minimum requirement for the range. The range works fine and does not trip the breaker. What am I missing here??

2. What is your opinion on the following options??

A. Replace the existing aluminum wire circuit with a #6 copper wire, 50
amp ckt? (Typical circuit application charts recommend a 50 amp
circuit for ranges 10KW to 20KW)

B. Replace the existing aluminum wire circuit with a #6 copper wire, 40
amp ckt? I figure that having the larger wire size already installed
would facilate any future power needs of a new range.

C. Replace the existing aluminium wire circuit with a #8 copper wire, 40
amp ckt?

Thanks, hope to hear from you soon.
 
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  #2  
Old 05-26-04, 02:32 PM
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I want to replace the existing aluminum wire circuit on my electric range.
Why? ......
 
  #3  
Old 05-26-04, 02:49 PM
Tom Lauer
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Replacing Alum Wire on Electric Range

John, The biggest why are the potential safety/fire problems associated with aluminum wire which I have read about in the past. But its more of a practical opportunity at this time, since I have upgraded my service panel to a 200A service and do not need the old panel any more.
 
  #4  
Old 05-27-04, 08:33 AM
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Aluminum wiring on large dedicated circuits is usually not a problem. The bad rap that aluminum wiring has gotten has all been associated with receptacle and lighting circuits.

What do you mean that your local power provider provides power at 80%? I surely hope you're getting 100%.

28 feet is nothing.

If the range manufacturer specifies #8 copper and a 40-amp breaker, then use #8 copper and a 40-amp breaker. Don't even consider anything else (unless you plan a new more powerful range soon). Although use of #6 is needless overkill for this range, use a 40-amp breaker even if you do use #6.

You must run four wires regardless of the range or earlier connection. Study the installation manual carefully. It should provide alternate instructions for 3 or 4 wire services. Follow the 4-wire connection information, even if the older installation was 3-wire. This may require you to make modifications at the range and will likely require you to buy a new range cord at your home center or appliance store.
 
  #5  
Old 05-27-04, 09:09 AM
Tom Lauer
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Replacing Alum Wire on Electric Range

John, thanks for the input. I appreciate it.

One more question. I'm still uncertain why a 40 amp circuit is recommended when the math suggests a total amp load of 52.5. Please explain.

Thanks.
 
  #6  
Old 05-27-04, 09:57 AM
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Beats me. But range and oven circuits, like motor circuits, live by a different set of rules.
 
  #7  
Old 05-27-04, 10:49 AM
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1) An extremely important thing to check: does the manufacturer specify 40A as the _required_ breaker for your range, or does the manufacturer specify 40A as the _minimum_ breaker and circuit for your range?
A) If the former, then you _must_ use a 40A breaker. 422.11(E)(1) spells this out.
B) If the latter, meaning if there is no required breaker marking on the appliance, and the manufacturer is recommending a 40A _minimum_, then I believe that 422.11(E)(3) sets the maximum value breaker that you could use. "If the overcurrent protection rating is _not_ marked and the appliance is rated over 13.3 amperes, not to exceed 150% of the appliance rated current..." Please note that I am unsure of this interpretation; others will have to double check my reading of the NEC.

2) While all of the heating elements in your range added together would result in 12.6KW of consumption, it is very unlikely that you would actually have _everything_ on at full blast for an extended period. Because the oven has a thermostat, you would really have to work at it to get everything on, and then keep everything on, and this is simply _not_ how ranges are used. So the NEC has a sizing table (220.19) which specifies the KW value that you use for sizing things like conductors, branch circuits, etc. For a single 12.6KW range, the number works out to 8.4KW, or 35A at 240V. So barring any other information, the NEC would permit a '35A' circuit for this range, and because of standard sized, this would mean a minimum of a 40A circuit.

Thus a 40A circuit with suitably sized conductors will be fine for this range. Depending upon the manufacturer's markings, you _might_ be permitted to go to a higher rated circuit (with suitable larger wires).

John touched on two point that are IMHO much more important than breaker size for this range.

1) Large gauge Aluminium conductors are generally safe. However it is _very_ important that all splices and terminations be made carefully. Use an anti-oxidant compound such as 'no-al-ox' on the terminations, and make sure that you tighten all connections to the manufacturer's specified torque levels. This does not mean 'squeeze as hard as possible', but instead means 'read the instructions and use a torque wrench'. Finally, double check that all splice and termination components are actually listed to be used with Aluminium wire. Properly installed, Aluminium is safe, but it is known to be harder to install properly.

2) Three wire versus four wire: In older versions of the code, it was permitted to run three conductors for the range circuit, and to use a single conductor for both the grounding of the range and for the neutral. This results in some current flow on the grounding system, and is no longer permitted. For a large single device such as a range, this was safe enough to be 'code legal', but unsafe enough that as code evolved this permission was eliminated. Modern residential range circuits are installed as 4 conductors with separate ground and neutral. If you have a three wire circuit that was properly installed under the old code, it is legal to keep it. However if you are gung-ho to replace your range circuits, upgrading from 3 wires to 4 is IMHO a much better reason than changing from Aluminium to Copper.

-Jon
 
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