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We purchased a Miele Oven (H6880BP) which has a NEMA 14-30 plug standard. The manual specifies 120/240V, 30A, 60Hz but does not have any instructions for a three wire connection.

Our supply is 10 gauge copper wire with three conductors (one is bare ground wire). It is 240V across the two hot legs and is a 30A double pole breaker.

It seems like I have the right power requirements, but am not sure how to connect the oven. I don't think I should use a pigtail to connect ground and neutral so what are my options? Running new four conductor cable would require ripping out plenty of drywall and cabinets. No go.

Thanks.

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    Can you post a photo of the inside of the receptacle box? – ThreePhaseEel Feb 11 '17 at 14:02
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    If you have 10/2NM cable as it seems you CANNOT use it for this 120/240V circuit. That cable can only be used for a 120V, or straight 240V, circuit. .................. If you use this for your 120/240V circuit the bare ground will be a current carrying conductor which is a big no-no. – Speedy Petey Feb 11 '17 at 14:48
  • Can you run just a ground wire somehow? Retrofitting grounds is legal now. – Harper - Reinstate Monica Feb 11 '17 at 16:50
  • I removed the receptacle so now there are just the three wires. I could borrow ground from the above oven which is on a separate circuit. It is #12 wire though. Then are you implying I could change the bare wire on my problem oven to neutral? – Farkus1982 Feb 12 '17 at 0:29
  • Also sorry I didn't respond earlier. I was looking for a notice in my inbox and didn't realize I had to check the site itself. I'm new, obviously! – Farkus1982 Feb 12 '17 at 2:33
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If your area uses the National Electrical Code then it has an exception for older installations that allows you to continue to use a 3 prong (NEMA 10-30) receptacle.

The appliance can usually be fitted with a 3 prong plug and the ground and neutrals are bonded in the appliance not at the receptacle.

Get yourself a 3 prong appliance whip from the box store and replace the cord on your oven. Look for information online your model and how to bond the ground and neutral inside the connection box.

Good Luck!

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    My only problem with this is that he says it is #10 wire, and one of the three is a "bare ground". To me this is 10/2, and CANNOT be used for a 120/240V circuit. Only SEU with two conductors and a bare neutral can be used in such cases. Do you agree? – Speedy Petey Feb 11 '17 at 14:47
  • Thank you for the comments. I can see the wire says "Encore 10/2 W/G type nm-b 600V." Looking at the panel, the black and white are both connected to the breaker. The bare is connected to ground. Could I borrow ground from the top oven? It is #12 though and straight 240V. Not 120/240V like the lower oven I am having questions about. – Farkus1982 Feb 12 '17 at 0:25
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    @Farkus1982, you do not need another ground, you need a neutral, which MUST be run in the cable with the other conductors. You can't simply run a separate one. – Speedy Petey Feb 12 '17 at 22:29
  • Speedy is right on that if you have only "10/2 with ground" coming to the receptacle it cannot be used for a 120/240 circuit. You need 10/3 with ground. – ArchonOSX Feb 14 '17 at 0:31
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For NM cable to be code compliant the ground would have to be insulated by the manufacturer which it is not. The code (NEC) exception would apply to existing SE cable only when the ground is bare (ART 250.140) The home owner does not want to bond the neutral / frame as that would be a shock hazard. The option is new wire or get really creative with a transformer to create a neutral. The right call is to contact a professional to insure the safety of your family.

Regards John J Deery Master Electrician

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    The bare conductor in SEU cable is a neutral, not a ground. – Speedy Petey Feb 12 '17 at 22:27

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