The National Electrical Code (NEC) rules are quite complicated regarding when an appliance requires an individual branch circuit serving no other load. In general, you will be following the NEC rules if you provide a separate circuit for each of the following:
The following appliances must always be grounded per NEC 250.114(3): refrigerator, freezer, air conditioner, clothes washer, clothes dryer, dishwasher, waste disposer, sump pumps, aquariums, personal computer, and fax machine. This grounding is especially important if the appliance is installed where a person can touch both the appliance and the ground or a grounded object. For this reason the NEC specifically includes motor-operated tools and electric lawn mowers and hedge clippers, etc. (A concrete floor, even if tiled, is considered the same as the actual earth.) For safety, always ground your appliances.
The one general exception to all of this is listed equipment protected with a system of double insulation. This equipment will be distinctively marked, and its attachment plugs won’t have a grounding pole. That is, they will mate with the A configuration shown here.
The grounding of ranges and dryers is discussed in specific sections later in this section. For other appliances, if they are supplied with a cord that includes a grounding wire, and a plug with a grounding blade fining a properly installed grounding receptacle, that is all that is required.
If there is no cord and plug but the circuit wires run directly to the appliance, and if the wiring is armored cable or in conduit, check to make sure the frame of the appliance is grounded to the junction box on the appliance to which conduit or armor is anchored. But if the wiring method is by nonmetallic-sheathed cable, you must use cable with the bare grounding wire, and the bare grounding wire must be connected to the frame of the appliance.
In the case of a water heater on a farm, if the wiring is grounded to a driven ground rod but there is some buried water pipe—no matter how short— you must interconnect such pipe with the ground rod. This is an essential step to prevent a difference of voltage between them and to minimize danger from lightning.
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