Replacement oven wiring question.

[DocHeb]

From my Breaker Box's 50A-240 breaker there is aluminum cable running to my oven. The aluminum cable has two hot leads and a bare aluminum neutral. The old oven pigtail had two hot leads, a white neutral and a separate green ground. Both the white neutral and the green ground were attached to the bare aluminum neutral wire from the supply lines.

1. Is this attachment of both the neutral and ground wire from the appliance to the supply neutral an appropriate connection?

2. The supply is aluminum, and the pigtail is copper. What is the proper way to connect these wires together?

3. We are replacing a double oven (with one pigtail) with a separate microwave and separate oven. Can both of these appliances be attached to the 50A single supply, or do they need separate breakers and supply lines?

 

[khd]

I'm not an electrician so don't shoot me if I'm wrong and don't take my advise without checking w/ someone who really knows but I just dealt with some of this when I redid my kitchen/laundry.

The 3 wire is old code using the same wire for neutral and ground. Unless you are using a sub panel, neutral and ground are the same inside the panel. When you wire a modern appliance to a three wire feed there is a bonding/ground strap to the appliance's frame. I asked my electrician if I should rewire the line with 4 wire and he told me there was nothing wrong with the way it was. When I got my new range I was expecting to have to attach the bond/ground strap but found it already attached so it was already set up for 3 wire. I did some research and there is alot of info regarding the safety afforded when you provide a direct and seperate ground (4 wire) hence the updated code.

I have always been told that directly connecting different wire materials is a no no and have a similar problem in my generator transfer switch (Aluminum feed vs a 12 g copper tap) I searched everywhere for aluminum 12g wire and was almost laughed at when asking at an electrical supply house (They do still make the stuff but is specialty wire used in hospitals and most don't even know about it) I again called my electrician and he said just use a spade connector on the copper and attach the spade to the aluminum feed....boy did I do a duh after all that searching. I'm not sure on space in your situation but you could terminate the feed in a 220 recepticle and then replace the pigtail with an appliance cord. I'm sure someone will have a better answer for you.

Is your micro a 220, I've never sen one of those? I believe a standard range circuit is 40A. Recommendation I believe on the 110 side for a kitchen is a dedicated fridge circuit and 2- 20a circuits feeding the rest in the kitchen. Micro's are a pretty big draw and if its a 220 version which I have never seen or dealt w/ such so I can't answer that one but the appliances should have some sort of amp/watt requirements somewhere add em up and see if 50a is enough.

Hope it helps a little but again I disclaimer everything I just said.

Regards,
Kevin

 

[Bird]

</font><font color="blue" class="small">( dedicated fridge circuit )</font>

Kevin, this house we bought in September did not have the breakers properly labelled in the main panel, and no labelling at all in the sub-panel for the shop. And I just finally started trying to figure it all out today. I'm not entirely through, but I do know that the refrigerator in the kitchen and the washing machine in the garage (opposite sides of the same wall) are on the same 20 amp circuit. So far, no problems and haven't had any breakers kick off.

And I do have the 40 amp 230 circuit for the kitchen range.

In '72 I bought a new house with aluminum wiring. There were florescent lights in the kitchen and one evening I smelled smoke and found a scotch lock burned up that connected the aluminum wiring to the copper pigtail for the lights. At that time I knew nothing about the copper vs. aluminum thing, but just assumed the problem was probably a loose connection when the house was built. So I soldered the two wires together and then put a scotch lock on them. In later times, I've read that you ain't supposed to do it that way but I never had any more problems with those lights.

 

[kenmac]

I'am not a big fan of aluminum wire, infact it is now outlawed in many places. I would upgrade to copper wire.Buy the new wire with 4 wires, nuteral -ground-(red hot) (black hot). A new 220 volt elec. clothes dryer is wired the same way these days.

 

[_RaT_]

If your oven needs 120V to run light bulbs, timers etc. from the 240V feed, you need a dedicated neutral and a dedicated ground. The best thing would be to replace the wiring if it is possible. I disagree with folks about aluminum wire. Aluminum wire has its place in the larger sizes with fixtures designed to accomodate it. Of course copper is preferable and a range uses small enough wire to go copper. Typically, you need a compression type connection for aluminum which eliminates wire nuts. The standard is a split bolt type connector. The problem with aluminum is the connection, not the wire itself. Aluminum oxide is a wonderful insulator. Aluminum oxidizes almost immediately when oxygen comes in contact with it. Clean it with a wire brush, use inhibitor and the correct connectors and it will serve its designed purpose well. Personally, for anything under about 4/0, I use copper. In the late 1960's they used #12 ALU for 15 amp circuits. This is where aluminum got its bad name and deservedly so. That was a major faux pau. If you score aluminum wire, it breaks quite easily. It was not designed to use in ordinary receptacles and its ability to take the stresses when making up the connections in standard boxes is poor. When unsure, go copper. New ovens today typically require 40 amp breakers which means #8 CU. If you ran #6 CU you would be assured that you could deal with most any electric oven designed for residential use. I am not sure I understand the microwave question. Is it part of the oven?

 

[khd]

Bird:

Before I redid my kitchen it was running off the same cicuit that also ran three beedrooms. I updated my service last summer to get off the old fuse panel and to be able to get the kitchen off the rest of the house. Washers arn't that big of a draw, and the problem with fridges are the start stop. I didn't take everyones advise and ran the undercabinet lighting off the fridge circuit. I to have no problems with it. I did do the rest of the kitchen with the 2-20a circuits because we lived so long with dimming lights everytime a small appliance started.

I do agree w/ Rat that aluminum does have its place in large feed applications (4 - the O range of gauges). The problem w/ small gauge aluminum back in the 70's was not the wire itself but was in the connections. Split nuts are the proper way to assure the connection will hold but never dealing with a hardwired range I've personally never seen it. You can pull 110 off a 3 wire 220 if the appliance is specifically doing it and not something that the user is doing outside the panel in a junction box hence the bond/ground strip. I would never split 220 off outside the panel i.e. if Doc's micro needs 110 service.

Doc: If your going to rewire the circuit to bring in 4 wire I would step down the circuit to 40a if appropriate and while your at it bring in a new 110 seperate feed for the micro.

I'll change out a recpticle or switch with the power on as that doesn't bother me. What bothers me about electriciy is making sure it is done right and safe so when I'm not home I don't have to worry about something going wrong.

Whew that was long winded.

Regards,
Kevin

 

[kenmac]

I agree Rat, that the large size alum. wire does have it's place .I was refering to inside house wiring etc,as in this case, wiring a range or other appliances.I used 00 alum. wire under ground to feed my garage from my house.I would never use alum.wire to wire a fixture or an appliance.

 

[DocHeb]

Thanks to all for your suggestions and comments. I think I will just pull replacement copper, mostly so I can have independent Ground/Neutral. I won't be the one doing any appliance replacement in the future, but with the floor being torn up this is the logical time to pull the wire.

For a run of 58 feet, what would the appropriate copper size wiring be for a 120/240-40A circuit? I've used an on-line calculator, and it reported that 8 guage is needed. Is that correct? It's interesting that the current supply is 8 gauge aluminum, which seems one size too small for 40A.

 

[_RaT_]

Yes, #8 is the correct size for a 40 amp breaker for an oven.

 

[Inspector507]

<font color="blue"> It's interesting that the current supply is 8 gauge aluminum </font>

That would be one size too small.