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8ga aluminum for 40A?

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Dec 14, 2013, 07:08 PM
8ga aluminum for 40A?
My new range will be rated 40A. Breaker is 30A, so I replaced it with a 40A but I see the wiring is 8 gauge aluminum. The run is approx 12 feet total. In Alaska, low ambient temps.

I also noted what seems to be some insulator melt (greasy substance) on both conductors right where they were stripped for insertion into the breaker.

I do have relatively cheap option to abandon existing circuit and put in a dedicated new run for range power from a nearby sub-panel off the service entry. Sub-panel was for a hot tub, but was installed with added capacity for a sauna, never put in.

Am I being over-cautious or am I correct that 8 gauge aluminum at 40A is asking for trouble?

Thanks for your thoughts!
Dec 15, 2013, 07:01 AM

That grease was to guard against oxidation on the aluminum wiring.

This message has been edited. Last edited by: joecaption,

Dec 16, 2013, 08:00 AM
You need to locate the nameplate on your range and note the total wattage, then divide by 240 [volts]. This number will then be multiplied by 150% and this new number will dictate maximum overcurrent and conductor size, per NEC {422.11}{E}. AS a range is a "non-standard Overcurrent device" you do have some leeway per NEC table 310.16, 334.80 and 338.{B}{4}{a].
Got all that? Big Grin

8 gauge aluminum does not list on my charts but if it did that safe use number would be 25-30 amps. And you are installing a 40 amp breaker. Here lies the problem.

Lets make this easy. 12' of copper Romex 8/3 [rated at 35-40 amps] with ground if purchased will set your wallet back a tad but you will sleep at night.

Please remember these numbers are pulled from the Standard Overcurrent Device Sizes charts that contain slightly different numbers that most copper sizing specs.

This message has been edited. Last edited by: CommonwealthSparky,

Popeye only reached for the Spinach can as a last resort...
Dec 16, 2013, 03:05 PM
Thanks to you both for your time and knowledge! I do find mixed signals out there on this topic, but you confirm my caution. I am leaving callback messages w/ electricians this morning to talk a new 40A range circuit as in my post.

New info: I assumed the existing range is 30A since that is the breaker capacity. Found previous owner papers yesterday; it is a 40A stove. Been here nine years of heavy use and 30A breaker has never blown. Maybe load rating for old stove was high. New range, however, will be double oven so I would guess that 30A - 40A draws are more likely.

If new circuit is delayed (rural Alaska = they will get to you when they feel like it) I am thinking put the 30A breaker back on the existing circuit and use the new range conservatively. Worst that can happen is the breaker trips, right?

Bad idea?
Dec 16, 2013, 04:12 PM
While at work I reworked the post in my head. Using the latest NEC guidelines #6/3 with ground CU [copper] NM cable is required. A 50 amp breaker is installed and 4 prong range outlet. Plus a 4 wire range cord is needed for the setup as well.
Now I would be fibbing if I told you what Alaskan rules dictate. Whomever you contact will have a good working knowledge of range wiring, Alaskan style. Big Grin I have a good idea, but it sure sounds like safety is paramount to you, as well it should be.
In a pinch using the 30 amp breaker & existing cable conservatively would in my opinion be what you have stated. Worse case being a tripped breaker.
Not sure if this helps but an oven itself uses less current that the burners do. {Remembering you now have two ovens. As you might have figured burners release heat into the air, while an oven keeps the confined.
PS, sorry about the brain freeze in the first post.

This message has been edited. Last edited by: CommonwealthSparky,

Popeye only reached for the Spinach can as a last resort...
Dec 16, 2013, 04:31 PM
Thnx again- got a journeyman scheduled for end of this month!

Love the internet.
Dec 16, 2013, 04:34 PM
always safest to protect conservatively. rural Alaska - fire department gets to you when they feel like it, weather cooperates, and hydrants are not frozen. capice?

#8 aluminum = #10 copper, generally you have to upsize aluminum one gauge for the same current in copper. #10 copper is 30 amps rated, derate as sparky says 150% and you have a 20 amp circuit continuous.

you do need the electrician, and a repull to serve the range. and it is not a real good idea to use aluminum wire for anything except line drops. it is permitted for a direct no-interruptions use, but it has this nasty habit of oxidizing on contact to air, making a high resistance connection. which means high heating, which causes the aluminum to expand and then shrink after current stops, loosening the connection, to repeat until ugly happens.

the only place I have added any is grounding my radio masts outside, using the correct Al rated studs and lots of No-Ox. the way you do that, even if you have "ick" inside the conductor on stripping, is soak up a green Scotchbrite with No-Ox and scrub down the conductors with it until you have lots of shiny and lots of black oxide on the Scotchbrite, then goop thoroughly and tighten the lug screw to spec with a torque wrench.

since the lug is also aluminum, ditto for the bolt through the lug.

you are better advised to pull new copper. the labor cost is going to be larger than the cost difference in the wiring, enough so it's not cost/risk effective to run copper.

we had aluminum going to the distribution pumps in the boiler house when I was in hospital maintenance as a glorified gofer, and it was replaced within a year due to issues. issues being wires kicking loose and burning through the motor wiring housings.

sig: if this is a new economy, how come they still want my old-fashioned money?
Dec 16, 2013, 04:34 PM
Good to hear. Wink
I answered your question this morning before going out the door, then applied NEC logic later.

Popeye only reached for the Spinach can as a last resort...
Dec 16, 2013, 07:57 PM
1. This place is an accumulation of skilled owner-built projects that began as a remote 16x20 cabin in the late 60's. Now 2100 sf. Road came in the late 70's, best I can tell electric came in late 80's. Kitchen and main panel are in the oldest section so stove circuit must be from first electric install. It is the only alum I have found. Existing range (being replaced) shows install in '94 so was surprised to find alum.
2. I hope to avoid a pull and just install a new four-wire run. Pretty sure pulling through existing run would mean demo and repair labor. Also panel is in a pain-in-the-neck location. But I know nothing. That is why God created professional electricians.
3. Hydrants?
Dec 17, 2013, 07:30 AM
Well it is hard to place a price on safety. Good to hear you will do all that is needed for a proper upgrade.

Popeye only reached for the Spinach can as a last resort...