Thank you very much for your help. Yes, you are right. It does sound like that he wired the fan to the master bedroom circuit and now moved the whole mess to the load side of GFI. I don't think he'll come back and redo the work. I waited him for more than 15 days before he came back and wired the fan switch to the load side of GFI. His expression told me he was very unhappy to come back and do the work. Although I paid him $1000 just for the labor of installing one fan and replacing another fan, material fees are separate. And no drywall repairment at all. I'll spend another $1400 for repairment of the drywall cut by the HVAC contractor for the fan installation and replacement. The circuit on the main panel that controls master bathroom also controls master bedroom, hallway, hallway bathroom, and another bedroom. So I think instead of putting a GFCI breaker on the main panel, it's better to wire the fan switch to the load side of GFI. But I did not expect it also affects the electricity in the master bedroom. I may have another electrician to fix it in the future after the drywall is repaired. Is it a big electric job? Thank you veru much for your recommendation of a good book. I'll buy and read it.

The green grounding wire and the white wire coming from the right side of the box are a bit of a mystery. What were they connected to? Are you sure there is not a black wire with them? Also, are there bare or green grounding wires coming from the top and bottom? Is the receptacle a GFCI (with a "test" and "reset" button)? If you can confidently answer these questions, especially the mystery ground and white wire, we ought to be able to help you. Otherwise, it would be best to call an electrician. A switch loop is the only place black would connect to white, and the white would have to be reidentified with a black marker or black paint at each end. But in your case, it does not appear to be a switch loop.

This is a common 'trick' for large loads like motors. By bringing out more of the motor windings from the stator the device can be used at more than one operating voltage. It increases the complexity of the windings though since they must be divided into appropriate sections and then the terminals made available. The same thing s done with motors designed for 120/240 V operation (not "high voltage" at all). It has littler to do with branch circuit wiring topology. You will notice we do not have 120 V bulbs and 60 V bulbs. This is what would be required to have some portion of alighting circuit in series and some portion in parallel. I personally do not do production wiring and use crimps for much at all. You will learn to dislike them when you start doing remodeling work and are no longer doing all 'new work'. I do charge extra when I am forced to deal with remodeling that has crimp connections. Simply cutting them off is often not an option since the remaining conductor length often then violates the minimum length required from the face of the junction box. I am sure it speeds up the 'production' installers though. Right now I have a house with a built in on one side of a wall, and a tile backsplash on the other in a kitchen. I need a couple new circuits for under-cabinet lighting. It looks like I will have to go through the back of the kitchen cabinets and fish upwards to the new junction boxes in the back of the upper cabinets. At least there are no crimps present in the boxes already containing some lighting switches.

Okay, forget your terminology for a bit. Visit NEC wording. You don't have a neutral and a ground. You have a "grounded conductor" and a "grounding conductor". Notice. Grounded, and grounding. One is an actual current-carrying conductor, which happens to be "grounded" (this is neutral). The other is used solely for grounding (this is ground). Once again, NEUTRAL AND GROUND ARE SUPPOSED TO BE CONNECTED TOGETHER AT THE MAIN PANEL. The ONLY difference between neutral and ground is that neutral actually has current flowing through it in normal use, where ground only has current flowing through it if something is seriously wrong. "current flowing through" and "voltage on" are different phrases. You SHOULD ALWAYS be able to see 120V between hot/neutral and also between hot/ground. Your measurements are normal and correct. There would be a problem if you DID NOT have 120V from hot to ground.