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-   -   Induction Cooktop, no neutral (?!) (http://www.diychatroom.com/f18/induction-cooktop-no-neutral-82426/)

andersol 09-26-2010 10:38 PM

Induction Cooktop, no neutral (?!)
 
I'm in Minnesota, hoping for some advice on wiring my induction cooktop. This is crazy to figure out: no neutral lead from the appliance! The specs are:

http://web.augsburg.edu/~andersol/wiring/photo9.jpg
http://web.augsburg.edu/~andersol/wiring/photo7.jpg

The install manual says:

"Frame grounded by connection of grounding lead to neutral lead. If used in a mobile home of if local codes do not permit grounding through neutral, open connection and use grounding lead to ground unit in accordance with local codes. Connect neutral lead to branch-circuit neutral conductor in usual manner.
Attach flexible conduit to the junction box.
CAUTION: To reduce the risk of electric shock and fire, do not use a flexible power-supply cord.
Connect the cooktop lead wires to the junction box supply wires in proper phase:
black (L1) to black
red (L2) to red
green wire to ground
If the cooktop is installed and connected as specified above, it will be completely grounded in compliance with the National Electrical Code. "

Here is my proposed wiring, 6 gauge.
http://web.augsburg.edu/~andersol/wiring/photo6.jpg
I would use the big blue wire nuts, for 6 gauge.

If this is indeed a case where, as they note "local codes do not permit grounding through neutral", they suggest to "open connection and use grounding lead to ground unit in accordance with local codes. Connect
neutral lead to branch-circuit neutral conductor in usual manner."
What the heck does "open connection" mean?

Some online forums seem to suggest that the wiring I propose would be
fine for a pure 3-wire 240V situation, but not for a 240V/120V
situation, where there are blower motors and other things in the
appliance. In that case, the forums suggest, a neutral must be
provided. I don't know how to make one up, if the circuit inside the
appliance has already mingled neutral and ground.

I have a 50amp breaker ready to go
http://web.augsburg.edu/~andersol/wiring/photo11.jpg

What is the right way to get this done?
Thanks to everyone for this great forum.
http://web.augsburg.edu/~andersol/wiring/photo10.jpg

kbsparky 09-27-2010 04:10 AM

How many leads (conductors) are hanging out of the flex? What size are they? What is the rated kW of your cooktop? You may not need such a large circuit. Can you take a close-up picture of the nameplate and the end of the flex?

Some manuals give generic instructions for different units. IF your unit does not even have a neutral wire in it, then that section would not apply. Look carefully at the leads coming out of the flex. Are any of them crimped together?

AllanJ 09-27-2010 07:19 AM

Quote:

Originally Posted by andersol (Post 507625)
What the heck does "open connection" mean ...

"Open connection" as stated there is an imperative clause with open being the verb and connection being the direct object.

Meaning, to disconnect the neutral wires from the ground wires, or to disconnect neutral wires from the chassis, and provide another conductor (green or white) as needed through the (flexible) conduit to the junction box.

kbsparky 09-27-2010 07:03 PM

Looks like you edited your post to add the pictures in after my initial reply. They do clear up a couple of issues.

From what I see here, your supply circuit is a bit oversized: The nameplate rating is 7.2 kW which = 30 Amps. A #10 wire and a 30 Amp breaker would have been sufficient.

Since you oversized your circuit conductors, you'll have to stick with that 50 Amp breaker, or else your equipment grounding conductor is too small to comply with the Code.

No neutral wire is needed for this appliance.

jddavis 09-27-2010 07:13 PM

Quote:

Originally Posted by kbsparky (Post 508002)

From what I see here, your supply circuit is a bit oversized: The nameplate rating is 7.2 kW which = 30 Amps. A #10 wire and a 30 Amp breaker would have been sufficient.

Since you oversized your circuit conductors, you'll have to stick with that 50 Amp breaker, or else your equipment grounding conductor is too small to comply with the Code.


How would it violate code by decreasing the breaker size to the correct breaker size? Would think at having a larger breaker size the appliance is not being protected like it should. Even though the wire size is larger than needed, no big deal.

Daniel Holzman 09-27-2010 08:04 PM

The breaker is not there to protect the appliance, it is there to protect the wires from overheating. You can use a 50A breaker with #6 wire, or you could install a 40A or 30A breaker. The appliance is almost certainly protected by an internal fuse, in any case appliance protection is the responsibility of the manufacturer.

jddavis 09-27-2010 09:15 PM

Quote:

Originally Posted by Daniel Holzman (Post 508046)
The breaker is not there to protect the appliance, it is there to protect the wires from overheating. You can use a 50A breaker with #6 wire, or you could install a 40A or 30A breaker. The appliance is almost certainly protected by an internal fuse, in any case appliance protection is the responsibility of the manufacturer.

Anyways you missed the point i was trying to make.. So, how does it violate code??? The point, not the way i phrased it:eek:

kbsparky 09-28-2010 04:47 PM

IT violates the code because you have essentially upsized the circuit conductors without a corresponding upsizing of the equipment grounding conductor.

The section of the Code you need to refer to here is 250.122(B):

Quote:

Size of Equipment Grounding Conductors.
(B) Increased in size.
Where ungrounded conductors are increased in size, equipment grounding conductors, where installed, shall be increased in size proportionately according to the circular mil area of the ungrounded conductors.
It seems silly, but it is a legal installation with #6 conductors and a #10 ground on a 50 Amp breaker, but it's a violation on a 30 Amp breaker.

Of course, your inspector-critter may not be bothered with it either way .... :whistling2:


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