Converting a 3-wire 240 Volt Circuit to a 4-wire 240/120 Volt Circuit

[Mike Cutler]

Bob

If you were to do the installation the way you describe, you would only have to rip it out when you sell the house. It will never pass a home inspection.
Run new service, if you really feel the need, but I don't think you need to. Even in Mass.
You are not installing new construction, but are simply replacing what is there. If the oven manufacturer has the instruction for a three wire hookup, use them.
Mass will allow you to convert the 3 to 4, and in fact, most "real" appliance stores, will already have a UL approved cable with the correct configuration, moulded plugs, at both ends.
I think you're over thinking what needs to happen.

[Curt Harms]

Hi Dan,

Yes, 2 #6 conductors plus a ground.

I'm not sure which range will be purchased. I've checked the installation instructions for some GE ranges and they state "All new constructions, mobile homes, recreational vehicles and where local codes do not allow grounding through neutral, require a 4-conductor UL-listed range cord". The instructions do show how to do a 3-WIRE INSTALLATION (GROUND IS THROUGH THE NEUTRAL WIRE) as well as a 4-WIRE INSTALLATION. I will have to check to see if the Massachusetts allows grounding through neutral for existing construction.

I take your point about the 14 ga wire being overloaded. If Massachusetts does not allow grounding through neutral, what about installing a single 6 ga wire in conduit from the service panel to the new box to use as the neutral and then have the new 4-wire cable going from the new box to the range?

I think the bolded line is your answer. The question is not whether it will work but whether it will cause problems with something like a prepurchase home inspection or (god forbid) insurance claim.

[Rollie Meyers]

A 3-wire feed to cooking equipment & clothes dryers is L, L, N, the receptacles used are 125/250V and are non-grounding devices, the frames of those appliances were & still are allowed in existing installations to bonded to the neutral for grounding purposes, ever since the adoption of the 1996 NEC, they have been prohibited in new installations, IMHO should have been prohibited decades earlier. As long as a existing 3-wire circuit is not altered, it is allowed to remain, a upgrade to 4-wire is always the best solution, but if it is not altered it's fine to leave as-is, as long as it's connected correctly at the appliance....

[Steve Milito]

For serious baking, electric tends to be preferred as it maintains temperature more keenly than gas fired. The only thing that kept me from doing dual fuel for our Thermador range was the added cost, quite frankly. The gas fired convection is pretty good with stability, but it still varies more than an electric oven would in the same configuration.

I disagree. Modern gas ovens with electric igniters have much less hysteresis than electric ovens. Gas burners heat up faster and stop generating heat almost instantly once the burner is off. Additionally, bakers prefer gas ovens because the relative humidity in a gas oven is much higher than in an electric oven, which is much more desirable for crust formation and heat transfer.