Proper Ground for 3 Wire Dedicated Cooktop Circuit

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  #1  
Old 09-15-14, 07:23 AM
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Proper Ground for 3 Wire Dedicated Cooktop Circuit

Hello,

I'm updating 2 appliance circuits for a second kitchen in my home. It's a 3rd floor rec room area.

The existing range wiring is insufficient to support both the new 50 Amp cooktop and the built in double oven. My plan is to use the existing 8 gauge wire for the new 6.7Kw double oven on the current 40 amp breaker.

This means I'll have to run new 6 gauge conductors and a new 50 amp breaker for the cooktop - about 100 feet long, all in EMT metal conduit per local Illinois code. I have space in an existing sub panel for the new 50 amp circuit but I'm a little confused about discreetly grounding this circuit (in the sub panel). The cooktop is a 3 wire, 7.4Kw (faceplate 50 amp) 220v with 2 hot legs and a ground. I imagine I'll run (3) 6 gauge wires - 2 black and 1 green. But, must the ground conductor be attached to a separate ground bus in the sub panel or can it be placed on the neutral bus? Alternately, can the cooktop ground simply be pigtailed to the appliance junction box with the conduit serving as ground? I think I know the answer to that already... Other ideas and suggestions welcome.

Other considerations - I'd like to stay with 3/4" EMT as it will be tricky to maneuver it up and through 3 stories and I'd also like to minimize my wire expense with the long 100' run for each conductor. I will make it 100% correct but overkill gets expensive at these lengths...

Thanks for any ideas.
 
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Old 09-15-14, 07:29 AM
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I imagine I'll run (3) 6 gauge wires - 2 black and 1 green
Only if they are 240v. If they are 120/240 you also need a white. The ground can be #10 or the EMT if continuous can serve as the ground.
 
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Old 09-15-14, 07:30 AM
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The ground conductor if run needs to go to the ground bus.

A metallic conduit like EMT with proper fittings and installation methods qualifies as a grounding means.
 
  #4  
Old 09-15-14, 07:46 AM
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Cooktop is dedicated 220v, no 110v.

So - using EMT compression fittings, etc (no screw clamp connectors) from the junction box behind the appliance all the way to the sub panel in the basement would allow me to safely ground the cooktop whip in the junction box directly behind the appliance?

Do I also have it right that there is a difference when grounding in the main breaker box versus dedicated grounding in a sub panel?

Thanks again for the lighting fast responses!
 
  #5  
Old 09-15-14, 08:15 AM
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Grounding in a subpanel is different than in a service panel.

Compression connectors are commonly called rain-tight and are not needed inside. Setscrew connectors are fine indoors.
 
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