I was looking at an electric dryer today in Home Depot. It said it could be wired with either 3- conductor or 4-conductor 220v service. There are two different plug types as well. Then I was looking at a spa-box (GFI disconnect) and it said it could be wired with either 3 or 4 conductor service. Of course in each case we are not counting the ground. What is the difference? When would I need/want 4-conductor for either my dryer or my hot tub?

The best and safest method for these types of appliances is the four wire system. Since the equipment ground is a definite, the neutral is mandatory for any circuit that uses the 120 volts, along with 240 volts. Only in special cases are the two allowed together.


Since the neutral is current carrying, the intent is to keep the equipment ground system free of any current.

Right, thanks. Like I said this is not counting the ground. (3 vs. 4 conductors). I already bought 10-3 wire plus ground for the dryer so I will go with the 4 prong plug. Better, right?

For the spa box what is more common? I'd hate to run a 6-3 romex wire for the spa box, seal up the walls, and then find out it would have been better to run 6-4 (or 6-3 plus an additional wire for 110).

Correct on the dryer, #6-4 with ground is typical for a spa.