I have 3 wire service that was directly wired to my old stove. The new stove came with a 4 pin plug. Can I use this plug or will I need to replace it with a 3 pin to match the 3 wire service? Or should I wire the service directly to the new stove?
That old 3-prong receptacle is dangerous. Upgrade to a 4-prong receptacle, by adding a ground wire.
That dangerous socket
The old 3-prong NEMA 10 receptacle doesn't have a ground wire. It bootlegs ground using the neutral pin - which is a terrible idea because any problem with the neutral wire will energize the chassis of your range. Appliance makers lobbied NFPA to allow this for "grandfathered" work, on the rationalization that these plugs are rarely disturbed.
The new 4-prong NEMA 14 receptacle includes a proper ground wire. If neutral fails, the oven light simply goes out. If neutral and ground fail, the chassis still will not be energized. Much safer.
Retrofit a ground
The NEC rules allow you to retrofit a ground wire separately, any way you can. It does not need to follow the same route as the power cables. It does need to go back to the the same breaker box, however.
You don't need to go all the way to the breaker box if you can reach another circuit which has a ground wire that's thick enough (and is also served out of that same box). Your minimum ground wire size is 10 AWG, and a water heater, dryer or built-in A/C will have that if it has a ground. Metal conduit is also a valid grounding path (make sure it isn't corroded, damaged or loosened). If the wiring is already in metal conduit, you're done :)
The cheapest way to buy 10 AWG ground wire is to actually buy 8 AWG bare copper wire, readily available at most hardware stores.
After that, you buy a matching NEMA 14 receptacle (probably 14-50) and connect
- The two hots to the two hots obviously.
- The grandfathered neutral to neutral (it may be bare; if so, wrap it with electrical tape so it doesn't contact the ground wire; bonus points for style if you use white electrical tape).
- The proper ground wire to the ground terminal. You don't want it touching neutral because that would defeat the safety benefit.
Check the range to make sure it's jumpered correctly for 4-wire and not 3-wire, plug it in, turn the breaker back on and enjoy!
(by the way, once you have retrofit the ground wire, you can also use that to ground other ungrounded circuits served out of that same panel.)
The New stove should have a diagram for you to wire it to 3-Wire Service. An electric range can be wired to work with either a 3-wire or 4-wire circuit.
Years ago (older homes) you had 3 Wire Service and many apartments are like this as well.
Newer homes have a 4 wire connection. L1 [BLACK], L2 [RED], Neutral [WHITE], and Ground [COPPER or GREEN].
In your case the home is older than the new electric range here's what you need to do: You need to purchase a 3-Wire Range Cord. Remove the 4-Wire Range Cord and install the replacement 3-Wire Range Cord.
Your manual will show you the proper connection for 3-wire service.
There is no way you can change the 3 Way receptacle to a 4 wire receptacle WITH OUT pulling new wire.
If you did simply change the receptacle this would be a code violation as the receptacle would not be properly wired.
Images from here >
Kens's answer is the best method. However in most areas, jurisdictions allow a grandfather clause. Meaning if the house was built in lets say 1994, then that house can stay under the NEC code it was built under (there are restrictions).
So, do not change out the female receptacle in the wall. You can buy a three prong cord cap and install it on the range. They sell these at most hardware stores. I would also check with your local authorities before doing this to see if they approve.
I am against hardwiring directly to your stove unless it's a built-in.