Our new dryer has 3 prongs vs. 4. We are changing to the new 3 prong dryer outlet, but want to make sure we are grounding. The wires coming from the wall our white, red & black - the the copper wire. Do I need to ground it?? Thank you! Molly
Switch the cord, not the socket
You have a proper NEMA 14-30 dryer receptacle with a ground wire, which is good. However, your "new" (old) dryer has a 3 prong (NEMA 10-30) cord. This can be rectified -- get a 4 prong (NEMA 14-30) dryer cord and install it on the dryer in place of the existing cord, making sure to remove the neutral-ground bonding jumper in the dryer.
You are not grounding, and this can kill you
I have no idea why you think 3-prong sockets are new. They are obsolete and dangerous. They are "exactly what they look like": the 3-prong outlet omits the ground, and the 4-prong outlet adds the ground.
Any problem with the neutral wire will result in the dryer frame being energized at 120V. Touching that and anything grounded, like the washing machine right next to it, will shock you.
It is illegal to convert a 4-prong to 3-prong. The home improvement store will happily sell you one, but they are only legal to sell for like-kind replacement which is not what you are doing.
The appliance manufacturers got a loophole put in Code so they could continue to sell appliances to old houses wired with the 3-prong outlets. In this case they bootleg ground, which is as bad as it sounds. Why on God's green earth the appliance store let one go out with a 3-prong plug is beyond me.
When reconfiguring the dryer for a 4-prong cord, make sure to remove the neutral-ground bootleg jumper. Neutral should be separate from ground.
The official name for the 4-prong is NEMA 14-30. The official name for the hazardous 3-prong is NEMA 10-30. Not to be confused with the safe but useless-for-your-dryer NEMA 6-30, which does have ground but not neutral.
I was just reading this and was going to comment about the "good old days" syndrome, when something hit me. Usually a dryer receptacle only has three prongs. I almost got caught up in the same argument, but a dryer has no need for a neutral it runs off of 240V not 240/120V and a standard receptacle provides slots for both sides of the 240V circuit and one slot for the grounding wire, and you usually run a 10/2 w/ ground romex to the receptacle.
I don't know why someone had a neutral for a dryer unless it was some sort of a special order. So he ordered a new dryer with the right configuration for a standard dryer. I would install a matching receptacle and wire nut off the neutral in the box.