EDIT
Thank you for the information. It doesn’t look like I was lucky enough to have a ground lurking behind the outlet. Our breaker box is located approximately 40ft from the receptacle with a difficult to reach attic space (vaulted ceiling) between the two. I’m not aware of any 50amp capable grounds that could be tied into any closer. What would be a fair price for an electrician performing the work needed to get a 4-wire receptacle installed? Just looking for ballparks.
ORIGINAL
We recently purchased a KFDD500ESS Dual Fuel Range which came with a 4 wire power cord. Our house was built back in the 70's, and we only have a 3 wire outlet. I'd like to remove the 4 wire power cord and install a 3 wire power cord, however I have a few concerns.
Based on my research, it looks like most ranges allow for this by allowing for a copper grounding strap that connects between the ground screw and the neutral terminal. However, the manual for this range doesn't say anything about it, and I do not see evidence of a grounding strap (which typically must be removed for a 4 wire configuration).
Would it be safe to take a thin length of copper and have it act as a grounding strap, connecting the ground screw to the neutral with the strap, then using a 3 wire cord? Similar to the grounding strap here: https://www.searspartsdirect.com/part-number/WB02T10067/0022/364.html
When it comes to the type of 3 wire cord, the manual states "This range is manufactured with a 4-wire power supply cord rated at 240 volts, 40 amps, rated at 194°F (90°C) and investigated for use with this range." Should I get a 3 wire cord rated for 40 amp or 50 amp? Is there a negative to getting one rated for 50 amp?
Here's some reference materials for the range, and some pictures:
Installation Guide: https://www.kitchenaid.com/content/dam/global/documents/201508/installation-instructions-W10694070-RevC.pdf
Best Answer
If the range does not have instructions for wiring with a 3-wire plug with hot1-hot2-neutral, then improvising would be out of the question, both for actual safety and for satisfying the code.
Without the range installed it is not that difficult to remove the receptacle and put in a 4-wire 50-A receptacle (NEMA 14-50). You can fit a 40-A or a 50-A breaker depending on what the wire allows, but can fit a 40-A breaker even with #6 wire. You would add a #8 or #6 copper ground wire (to match the existing conductors) going back to the panel. Or if it is available, connect by tap onto the heavy, uninsulated ground in your attic that goes back to the panel. Use a split bolt connector to tap. The added ground does not have to follow the route of the existing conductor.
First examine the contents of the box. Of course, shut off the breaker, then pull out the existing 3-wire receptacle and see what size wire you have. How many conductors do you have? Probably just three, but maybe you'd get lucky and find an unused ground coiled up in the box.
EDIT
You should at this point contact your local electrical code enforcement and ask them about the approach outlined above. If this is allowed, then it would not be dead easy to fish a ground down into the wall and into the existing box. Someone here would have to tell you the practicalities on how to do it. What may happen here is that you will learn from the experts here what is a reasonable arrangement, and if you have never done this before and need it done without delay, then you might have to hire an electrician, but at least you would have in mind your instructions to the electrician.