I stand corrected. There is a certain level of hazard in using refrig or washers that trip a GFCI, but the Code allows you to live with it. You probably have non-GFCI outlets for these appliances-so you do not know if they would trip a GFCI or not. Same as the old 3 prong electric ranges, dryers...the frame carried the neutral current...but it was Code legal until about 2005 or thereabout, depending if you are in a MBH or stick house. But all the existing 3 prong dryers and ranges are still grandfathered in..how about that hazard?
250.140 Frames of Ranges and Clothes Dryers.
Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be grounded in the manner specified by 250.134 or 250.138.
Exception:
For existing branch circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be grounded to the grounded circuit conductor if all the following conditions are met.
(1) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.
(2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.
(3)
The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.
(4) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.
It ain't just as simple as being a three wire as outlined above.