Al to Cu Cooktop Connections

Discussion in 'Electrical Forum discussion & Blog' started by TubeGuru, Sep 6, 2010.

  1. TubeGuru

    TubeGuru New Member

    Messages:
    11
    Location:
    Redmond, WA
    I just replaced my 120V cooktop, and now its time to hook it up. The 50A service is fed through #8 stranded Al Type SE cable, and the cooktop has #12 stranded Cu. Its pretty clear to me from researching the topic that Al-Cu connections have to be done right, if they can't be avoided altogether.

    The original connection (done in 1983) was a wire nut and de-ox grease, and there was no sign of oxidation or overheating. I'd go that route but I can't seem to find anything other than copper-to-copper wire nuts. Are those acceptable to use, even with Ox-Gard?

    The other options would be ILSCO aluminum split bolt connectors or ILSCO crimp connectors, installed in a junction box. I'm leaning towards having a pro install a junction box and use crimp connectors. That seems to be the most permanent, reliable and safest method, short of pulling new copper.

    I'd be interested in what the pros think.
  2. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    1,001
    Location:
    NY State, USA
    First off, the #8al is not good for a 50A circuit. What is the kW rating of the new cooktop. With #12 leads I would think it is around 4.5 - 5 kW.
    Be sure to replace the breaker with the appropriate one.

    I would use NSI IT-4 Insul-Taps for the conncetions. Super simple. Super safe. Super easy. The only thing is they are not super cheap.
  3. TubeGuru

    TubeGuru New Member

    Messages:
    11
    Location:
    Redmond, WA
    It's a Jenn-Air JED8230, rated at 4.3 - 8.0 kW @ 120/240. It's also a 3-wire (red, black, white) whereas the old Jenn-Air was 2-wire.

    The built-in GE oven/microwave are on the same circuit as the cooktop, which is perhaps why it has a 50A breaker.

    Update: it may be #6 Al. The ink is smudged and blurry but it looks more like a 6 than an 8.

    Thanks for taking the time to reply!
    Last edited: Sep 6, 2010
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,247
    Location:
    Cave Creek, Arizona
    8kw is MUCH too great a load for # 12 wires. Even 4.3 kw would call for #10.
  5. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    1,001
    Location:
    NY State, USA
    The #12 is the factory whip that comes on the unit.
  6. TubeGuru

    TubeGuru New Member

    Messages:
    11
    Location:
    Redmond, WA
    I talked to an electrician today, who raised a couple of questions in my mind. First is that he said it should be on its own 30A breaker. This makes sense, since the cooktop and separate oven/microwave combo are on the same 50A circuit, and that's no protection against a fault in the microwave. There is only one SE cable going into the load center, so it must be split somewhere in the attic or crawlspace. So, continue to share the 50A, or establish a new circuit?

    The other thing he said is that he doesn't think the cooktop would need 4-wire feeder. The white neutral on the cooktop would be connected to the bare ground wire on the feeder. This doesn't "feel" right, if you know what I mean.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    You only need neutral if there are any circuits that use 120vac in the cooktop (clock, lamps, timer, etc). It will say whether it needs it or not. Often, the installation instructions say to run separate circuits for the appliance. It's always safest if you do that, and is required if that is in the instructions as mandatory.
  8. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    You said the original wring was 2 conductor. This would olny be suitable for a straight 240 cooktop. you saidthe new unit is 120/240. You need to run a new cable and install the proper size breaker.

    The microwave should be on a completely different circuit, preferably its own dedicated circuit.
  9. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    1,001
    Location:
    NY State, USA
    A dedicated circuit certainly would be best, but it is not mandatory.
    Also, his comment about no protection against a fault in the micro? The breaker does NOT protect the appliance, it protects the circuit conductors.
    The setup the way you have it now is expressly allowed in the NEC.

    The cook top does not "need" a 4-wire feeder because the feeder cable is SE cable. The bare wire in that cable is a neutral, NOT a ground. THis is the only time a bare wire can be a neutral. This is also grandfathered in, you could not a new circuit like this.
    Again, a new 4-wire feeder would be better, but not mandatory.
  10. TubeGuru

    TubeGuru New Member

    Messages:
    11
    Location:
    Redmond, WA
    Jim in VT: The fan is 120V and the burners are 240V, which I assume is why the rating plate says "120/240 or 120/208". The instructions say "three-wire, single-phase, 120/240VAC..."

    Jim in MD: The service feeder, as Petey pointed out, is 3-wire. The old cooktop had the feeder neutral (bare wire) connected to the cooktop ground (chassis). That is why I called it 2-wire.... to me it had black, red and ground. But it's all 3-wire.

    Petey in NY: Well there you go! I'd never have guessed that the bare wire was neutral.

    A table for the cooktop indicates that for 7.0-9.0 kW, a 40A breaker and #8 wire be used.

    Can anyone tell me why the rating plate has a range of 4.3 - 8.0 kW ?
    Last edited: Sep 8, 2010
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    The burners have a 'low' setting. Voltage could be higher or lower than normal, so the overall current can go up or down, plus, the tolerance on the controls and heating elements may not be exact per spec, but still work fine (i.e., they may have a range where they are acceptable). So, while there may be one 'perfect' load, given the nature of things, the actual use will vary.
  12. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,247
    Location:
    Cave Creek, Arizona
    The amperage range is probably from the minimum at the lowest setting, to the maximum, possibly with all the burners in use. Some burners use 110/120v for the lower settings.
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