As a general rule, the bigger the appliance, the larger the wiring and the more voltage required. Small, portable appliances such as blenders, coffee makers and T-Vs can be plugged into a standard 120-volt outlet. Larger appliances like electric water heaters and cooktops must be supplied with 240-volt wiring, to accommodate their greater electrical demands. But there are exceptions: a refrigerator, though large, may need only 120 volts; whereas certain dishwashers with powerful heating elements may take 240-volt wiring. Each device should be labeled with a rating, as to what electrical specs are required. There are also limits on how many appliances can be connected to the same circuit; for example, no more than two ovens may be on the same circuit as a cooktop. A good electrician should be up on all the latest codes, and understand the basics of safe wiring. So if you're adding appliances and have questions, consult an electrical contractor.