I recently completed a number of upgrades to my CR-10S4. These included replacement of the motherboard (with EZBoard Lite) and Keenovo AC heated bed. In line with good electrical safety practice, it is important to check that any conductive enclosure (e.g. CR-10 control box) is securely bonded to electrical ground. This is particularly important when using the existing cable for a 120 or 240V AC supply to your heated bed.
You can determine if your CR-10 box is properly grounded by connecting a DMM or VOM between the ground terminal of the incoming power, AC plug and any bare metal surface of the box. A reading of approx. 1 ohm or less indicates a sufficient ground bond. A higher value of resistance, or even an open circuit, means that a potential shock hazard exists. The factory installed a green/yellow wire which runs from the incoming power AC ground terminal to the ground terminal on the Power Supply. Since the Power Supply is physically connected to the control box with four screws, these screws serve as ground bonding conductors. Make sure these screws are tight. If you need to remove your Power Supply for any reason, be sure to replace all four screws and make sure they are tight.
Since I believe in belts and suspenders (braces) when it comes to electrical safety, I added an extra jumper wire between the AC ground terminal and control box.
Note 1: There have been reports that the ground terminal on some Power Supplies is not connected to the power supply case. If you find this condition, you have a defective power supply and a shock hazard. Replace your power supply and check that the ground terminal and case are connected and that this connection measures less than 1 ohm.
Note 2: There is another potential shock hazard that I discovered. The second photo shows the back of the control box where the cables are I found that the metal sockets (the shiny part connected to the box) where not connected to ground. If you run your 120-volt bed circuit through this socket and a short occurs. You can receive a serious shock if you touch these parts. I removed both sockets and found that they were insulated from the case by the material used to finish the case (either paint or powder coat). I used a small metal file and piece of sandpaper to completely remove the finish around the holes. I replaced the sockets and measured 0.2 ohms between the socket and case.