John, it is a mystery to me. In the 3520C documentation
OK, Lou, out of a sense of intense curiosity I pulled up the owner's manual for the 3520C and I think I've solved the puzzle. I had heard that the 'C' model ships without a power cord and was wondering why they would do such a thing ... figured that out too. So, from the owner's manual:
- Page 11, Section 7.0: "This lathe is shipped without a cord. This lathe must be permanently connected to the electrical system in accordance with the National Electrical Code and any other applicable state and local codes. Extension cords should not be used with this lathe. Consult a licensed electrician if you are unsure how to properly connect this lathe to the building’s electrical system."
Apparently, they really, really want to prevent the owner from using an extension cord. The power supply cable is to be routed from a 20 amp circuit breaker or time delay fuse and connected to the "Main Switch box" (fig.7.1).
- Page 16, Section 9.0 (A): "Power switch: Activates power flow to inverter and motor." See figure 9-1.
Note here that the name of the switch has been changed but it's the same switch. Note also that the switch "activates" power to your machine. In other words, it does the same thing as plugging in and unplugging. Note also in figure 7.1 that the left position of the switch is labeled "O", indicating an open circuit, and the right position is labeled "I" for a closed (or connected) circuit. So, yes, the Power or Main switch is intended to be used instead of plugging in and unplugging.
- At the end of Section 9.0: "Caution: A lightning strike or power surge may cause the inverter to fail. When lathe is not in use, disconnect power plug, or have a 3-pole disconnect installed on the power side."
This, I think, is a holdover from the previous models (I have the 'B') which do not have a Power disconnect switch. Your Power switch serves the purpose of a disconnect. Note that it contradicts section 7.0 and is, therefore, a technical error in the document .... as is using two different names for the same switch by the way. What it does tell us correctly though is that we're not to leave the lathe plugged in or the Power switch in the "I" position when it's not in use.
Here, again, it's called the Main switch and is shown in the upper right of the wiring diagram. It shows it is "upstream" of the inverter and motor and serves to disconnect power from the lathe.
So, in summary, if your 3520C is plugged into a wall outlet (in violation of the owner's manual ... sorry, that's just what it says) then you have two ways of disconnecting power. You can unplug or you can turn the Power switch to "O" ... or both. If it is "hardwired" to your distribution panel, then you would use the Power switch to disconnect power and provide protection against power surges. I hope that helps.
Reference:
https://content.powermatic.com/assets/manuals/1353001_man_EN.pdf