Wiring oven and cooktop to aluminum supply wires


I am remodeling my kitchen and have a new wall oven and a new cooktop. In the wall, there are separate junction boxes containing 240-volt aluminum wires for the oven and the cooktop. Each junction box has four aluminum wires -- two black, one black with a barely recognizable white strip and a bare wire. The bare wire is connected to a lug screwed to the metal box.
My question is how to wire the two appliances. The oven comes with a four-wire copper cable. I suppose the bare wire from the oven should go to the bare ground wire, white should go to the white-striped neutral wire and black and red should go to the two black wires. Are the two black wires in the wall interchangeable? If not, how do I know which one goes to the red from the oven? Why are there four wires in the first place?
The cooktop, on the other hand, has only three wires -- red, black and bare copper. Why no white? How should I match up the three cooktop wires with the four wires in the wall.
I realize I need to use antioxidant in the wire nuts when connecting aluminum to copper. Any other precautions needed?
--Bob
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BobH wrote:

Hi, Do you have multi meter? Also wire nut should be Al-Cu compatible. Oven takes 240V and it uses 120V off it. Two black is hot and one white strip ought to be neutral. Top is using only 120V so you'll have to connect it to one leg of 240V between a black and neutral. Double check with meter.
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wrote:

Maybe... given his description, it's hard to tell exactly what he has. No way should there be three black wires and one bare one in a junction box.

WRONG WRONG WRONG WRONG.
The cooktop is using 240V -- as *clearly* shown by the use of red and black lead wires with no white. The red and black lead wires must be connected to the two legs of the 240V supply, and the bare lead to ground.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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BobH wrote:

Hi, Can you tell the power requirement for the cook top? From the sticker or manual? Also do you have a multi-meter of some sort?
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Tony has the wall oven wiring correct, but the cooktop is 240 volt not 120 volt. Connect the red and black from the unit to the two black feed wires, and connect the bare wires together and cap the "black with white stripe"

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Some appliances don't use a neutral

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this)@optonline.net> wrote:

True -- the OP's cooktop appears to be one of them -- but the electric oven *does* use a neutral. The heating elements are 240V, but the control circuits (clock, timer, etc) typically run off 120V.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Thanks for the answers, but I'm not quite clear on some details. I probably should have posted the oven and cooktop questions separately. Let me try this again.
First, three clarifications:
A. In the cooktop junction box, one of the wires has red markings on it, so there I can distinguish between red and black. In the oven junction box, the two blacks look identical.
B. The cooktop clearly takes 240 volts. It is marked 240/120V.
C. I don't have a multimeter.
Questions:
OVEN
1. Is there any difference between the two black leads in the oven box? Does it matter which one goes to the black oven wire and which goes to the red oven wire?
COOKTOP
2. Does everyone agree I should just put a wire nut on the white-stripe wire and not connect it to anything from the cooktop?
GROUNDS
3. In both junction boxes, the stranded aluminum ground is attached to a lug screwed to the metal box. The oven ground wire is relatively thin copper, and the cooktop ground is relatively thick copper. What is the best way connect them to the box ground wire? Should I use Al/Cu wire nuts on the part of the aluminum that extends past the lug?
MULTIMETER
4. If I go buy a multimeter, is it going to be obvious which wire is neutral? How will I know?
CONNECTORS
5. I have seen expensive Al/Cu nuts from the Ideal company (about $5 for only two nuts). I think they have antioxidant inside. They look a little small for my wire, though.
I also have some larger wire nuts and a tube of antioxidant. As I understand it, the preferred practice when using wire nuts is to tape them after twisting the wires together and embedding antioxidant in the nut.
Another recommendation I have seen is to buy a special aluminum-to-copper "bug" that has separate screws or clamps for the two wires, and to tape it up after connecting the wires.
The old oven and cooktop had wire nuts with antioxidant in them. Which is the preferred method?
--Bob
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BobH wrote:

No difference/doesn't matter.

Assuming it is the likely neutral I agree. If they are on the same circuit (same fuse/breaker) IIRC the max size is 50A.

Reasonable. If the wiring to the oven/cooktop is in flexible metal conduit (not flexible cord) that is part of the ground.

120V to each hot, 0V to ground

There is information on making aluminum wire connections at http://www.inspect-ny.com/aluminum/alreduce.htm which is based extensive research, primarily for the Consumer Product Safety Commission. It does not like the Ideal wire nuts, prefering 3M wire nuts and antioxide paste.
Someone discovered a more recent product http://www.alumiconn.com/details.html but the max wire size is only #10
--
bud--




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Thanks for all the answers. One more thing:
What do you think about using a split bolt connector rated for aluminum and copper. Apparently the wire nuts are too small for these wires, which I think are 6-gauge stranded aluminum on the 50-amp oven circuit and 8-gauge stranded aluminum on the 40-amp cooktop circuit.
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BobH wrote:

Split bolts are good but kind of a pain to insulate (plstic tape).
-- bud--
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So far, I haven't found any connector made for No. 6 aluminum and No. 16 copper. A split bolt I've seen is for 6 through 10, and a Polaris I've seen is for 4 through 14. An installer says he uses a wire nut, which an inspector and some electric supply guys think is a bad idea. What would you do?
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this)@optonline.net> wrote:

The black with white stripe is probably the neutral -- although I sure wouldn't assume that, without verifying it with a meter -- in which case it should be connected to the white lead for the oven, not capped.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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BobH posted for all of us...

Asked and answered MANY times! Sorry, you lose, buh bye, bring in the next player Johnny.
--
Tekkie Don\'t bother to thank me, I do this as a public service.

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