I have a few wiring questions. I am completely re-wiring an old house. I have a double oven and an electric Kitchen-Aid cooktop with a grill in the center that were salvaged from a home that was being remodeled. Both are in very good condition, but could be 10-15 years old. I cannot find any info (a tag, plate) on the cooktop, and so far the same is true for the double oven (though I have to pull them out to check the back side). Also, there are no manuals for them. I need help to verify the gauge of the wire to be run to each and how to wire them.
For the double oven, from what I have read, I will need a 50 amp circuit with 6/3 wire. For the cooktop, I think that I will need a 40-amp circuit and 8/3 wire. Does this seem correct?
Next question is that both have a whip with 3 wires (not four) in them. How do I connect a 3-wire whip to 4-wire service or is that even allowed? I’d like to use both of these as they are hardly used and in very good condition.
Thanks in advance for your advice.
Replies
>>>Next question is that both
>>>Next question is that both have a whip with 3 wires (not four) in them. How do I connect a 3-wire whip to 4-wire service or is that even allowed? I'd like to use both of these as they are hardly used and in very good condition.
It can depend on a couple of factors. What color are the wires?
Keep looking...there oughta be a spec plate or label there somwhere.....
Double oven/cooktop wiring questions
There is no tag that we can find on the Kitchen Aid cooktop. It has a red, black and bare ground in the whip. (Also, it is a 4-burner top with a built-in grill - not broiler).
The double oven is a Maytag model MEW6630. We found a tag with the following info on it.
"For use on 3-wire systems. 120/240 volt 7.2 kW or 120/208 5.4 kW"
The whip for the double oven has red, white, and black wires - no ground.
Maybe DanH can remember the detail on this (He'll likely jump into this thread, with his cape billowing in the wind, later today.)
If you cue up the music to Wagner's Ride of the Valkyries, he might don his Super Dan outfit a little quicker..... ;-0
There used to be a time when the equipment ground and the neutral were bonded together inside electric cooktops and ovens. This is a no-no today. The fact that the oven says 120/240V, but doen't have a bonding conductor, makes me think this is the case.
I probably woundn't use either one of these units until I had the OK of the local electrical safety authority.
Sorry, my cape is at the cleaners. But, yes, it used to be common (as late as about 1975, depending on locale) to connect 120/240V appliances with a 3-wire pigtail.
However: 1) Many/most appliances built since about 1965 were actually made "agnostic' with regard to this point and could wired with either a 3- or a 4-wire pigtail. What was required was to remove a jumper between the ground and the neutral connection, and connect the 4-wire cord. 2) Many more recent ovens and cooktops are built for 240V only, with no need for a neutral connection.
I would likewise advise against using an oven unit that says "120V/240V" and doesn't have an identifiable neutral connection (though possibly currently tied to ground with a jumper). Such a unit would necessarily be pretty old anyway, and not what you'd want for new/remodeled construction. If the unit says "240V" (or (208V/240V), however, it should be good to go with a 3-wire setup.
I'd also be reluctant to use either unit until I had a good handle on the current requirements (preferably a peek at the nameplates). It's not good to "overfuse" an oven or cooktop, as there are a number of failure scenarios where this could lead to badness.
More to the point
Does either the cooktop or double oven have a 120v component included such as timer, electronic controls, light, etc.?
If NOT, then the 3 wire connections are legal, yesterday and today. 2 hots + ground.
If there IS a 120v component, then you would need a 4 wire (neutral is #4).
7.2 kw = 7200w = 7200/240 = 30A max draw
30 x 1.25 = 37.5A min. acceptable breaker ---- 40A breaker, #8 copper wire
All that being said, I would contact Maytag and Kitchen Aid re: 4 wire conversion if 120vac devices present.
Jim
Re: More to the point
Regarding the cooktop: It has NO 120 v component, no timer, electronic controls, etc. Again it has a red, black, and bare ground in the whip. I have also looked around at a number of models like this and none requires anything more than 40 amp circuit and 8 gauge wire.
Regarding the double oven: It has some 120 V components, a timer, electronic controls, and lights (it is a pretty modern system). I also downloaded the manual for this model from Maytag's site and it indicates that 8-gauge wire should be used, but the drawings only indicate a 4-wire whip. I triple-checked again tonight and I can only find the 3 wires - red, black, and white. I couldn't pull the ovens out as we were working on the floors. I can do that later. So I am wondering what to do. I can try to call Maytag and see if someone can help me. However, the manual has confused me - perhaps it is for a more recent version of this particular model double oven.
Then manual also says "If codes permit and a separate ground wire is used, it is recommended that a qualified electrical installer determine that the ground path and the wire gauge are in accordance with local codes. Check with a qualified electrical installer if you are not sure the oven is properly grounded. This oven must be connected to a grounded metal, permanent wiring system."
Manual also says 40 am service - 8 gauge wire required.
It's not at all unusual to find a 4-wire unit wired to a 3-wire pigtail where it had been installed in a home more than 30-40 years old. When you take off the cover where the wire enters you'll likely find a jumper between neutral and ground.
Double oven/cooktop wiring questions
OK, thanks for the advice. I'll pull the oven out and check.
What is your advice regarding the cooktop? I really hate to throw this out. It is in very good condition. I did check where the whip enters the cooktop and cannot see any evidence of another wire or a jumper. Is it safe to install this do you think?
I suspect, .....
.....like DanH, that the double oven has been rewired from the 4 wire factory configuration, to the current 3-wire configuration to allow use with an existing house circuit. This was a very common practice.
A new 4-wire circuit would be black (L1, hot), red (L2, hot), white (neutral for the 120v components), and bare (oven frame ground). The double oven will work perfectly without a frame ground - just not with the desired safety margin provided by a seperate ground conductor. As DanH said, there may be a jumper present between the existing white neutral and the frame - also may not be - much stranger things have been done / found.
I suspect that the situation will be much more apparent once you have the oven out of the wall and the electrical connection plate open. At that point the manual will probably make more sense - if not - call Maytag for confirmation.
Manual did provide confirmation of 40A breaker and #8 copper wire.
Re: cooktop - no 120v components, all 240v = no neutral required, not yesterday, not today. Black = L1 hot; Red = L2 hot; bare = frame ground. Breaker size and wire gauge remain unconfirmed - contact KitchenAid.......by far the best option.
Last resort emperical method: To avoid any major rework, I would rough in the circuit with #6 cu (this would allow a maximum legal breaker size of 50A), connect to a 40A breaker, measure the actual amperage draw with a clamp-on ammeter and then change breaker sizes up or down as indicated by the draw.
You will already have a 40A breaker on hand for the oven, so your "experiment" will only cost a trip to the supply house for the right-sized cooktop breaker plus the difference in wire cost #6 vs #8 - pretty cheap for a free cooktop. As a bonus, assuming the cooktop only requires a 40A breaker - it will be very happy with the increased voltage it is getting through the #6 due to a decrease in voltage drop!
I suspect you will have a very hard time finding 6/2 with ground (or 8/2 with ground) - you will probably end up running 8/3 or 6/3 with ground - in the case of the cook top, the white conductor will be unused and can be capped and coiled at both ends, or clipped off. I would tend to leave it intact for future upgrades. Pay attention to J-box sizing.
Good luck!
Jim
Double oven/cooktop wiring questions
You were correct. Pulled the oven out, took off cover where the whip enters the oven and there was the ground. The original installer had clipped off the ground at the end of the whip and shoved what was left up inside. In other words, I think they must have only had 3-wire service. Hooked up a new ground wire and we are in business. Thanks for the advice.
As far as the cooktop, I intend to follow your advice.
Thanks again all for your help.