Can I wire a water heater and a tanning bed on the same 220V breaker. I live in Ohio.
You need a dedicated circuit for these appliances: Refrigerator, Freezer, Electric range, Microwave, Water heater, Washer, Dryer, Dishwasher/garbage disposal, Furnace, Heat pump, Air conditioner (central and window), Sump pump, Hot tub/Sauna/Jacuzzi
A furnace requires a dedicated circuit.[422.12]
Dwelling units require at least one receptacle outlet for the laundry area. [210-52(f)] Laundry receptacle outlets in dwelling units must be fed from a 20-ampere branch circuit. Receptacle outlets outside of the laundry area are not permitted on the laundry circuit. [210-11(c)(2)]
If an appliance is a chord and plug type and it exceeds 80% of the branch circuit rating then a dedicated outlet is required. If the appliance is fastened in place and is rated for more than 50% of the branch circuit then that circuit must be dedicated. [210-23(a)]
Here is a terrible reference, but: http://electrical.about.com/od/appliances/qt/DedicatedCircuit.htm makes a good point, "A good rule of thumb is that if it has a motor, it needs its own circuit."
Even if you could it is not at all a good idea. Bottom line is if the water heater is on a 30A circuit then you CANNOT do this unless the tanning bed draws approx. 6 amps or less, which is highly unlikely.
The max load on a 30A circuit is 30A, and the limitation is 125% of a continuous load (a storage water heater is to be considered a continuous load, so just under 24A for a 4500 watt unit) plus that of the non-continuous load.
210.19 Conductors — Minimum Ampacity and Size (A) Branch Circuits Not More Than 600 Volts. (1) General.
Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.