Simplex 4004: Do I need three ground wires on one lug???

Okay, so on my 4004 I have the following ground connections made:

  • One that goes from the panel cabinet to the plug’s ground. Note that the plug is plugged into an extension cord which in turn is plugged into a surge protector power strip and said power strip into a GFCI outlet (which is hooked into my furnace; and it’s the only outlet in my entire basement besides the one next to the main electrical panel for my house). This connection is on the same lug as the door-to-cabinet ground because replacement grounding screws wouldn’t fit, so my dad decided to use this instead and it works fine. The panel does NOT display any ground faults or troubles besides the battery trouble (because I have no batteries nor am I intending to get any).

  • The next connection is the door-to-cabinet connection. This connection was made when I already got the panel, and works fine.

So, my question is, while watching a YouTube video of kcin’s new panel, I noted that he had made three connections. Two of which are like the ones I have already made on my panel. However, I inquired what the third ground wire was, and he told me that this was something called a “chassis ground”. So, I don’t really know what a “chassis ground” is, but I can assume in 4004 terminology it is the metal piece that holds the motherboard/filtering capacitor/CPU etc.

So my question is: What is this chassis ground, and is it absolutely necessary? I assumed that since the metal piece is connected to the cabinet, it would be protected because the cabinet and plug are grounded, right? I’ve powered up the panel many times without issue, so is this something I need to address or is this not an issue due to my setup? I’d like to know so I don’t fry it or it surges and something goes bad, because I don’t have another $320 to spend.

Thanks!

Here’s the wiring configuration in my panel that prompted this question, for reference.

As you mentioned, there appears to be three grounding connections. The wire with the yellow terminal is the incoming ground wire from the plug. The wire with the blue terminal connects the cabinet to the door, just a short jumper basically. Finally, the wire with the red terminal connects to the chassis ground on the panel. They chose to route all of the grounding to one lug on the cabinet, rather than two separate connections, which requires the three wires you see.

At the upper right of the image you’ll see the wire with red terminals is bonded to the grounding post on the power supply chassis. Keep in mind, this was a factory-installed connection.

The way you have the power cord green wire connected to the box to door ground stud should be fine. The green screw is there to meet code requirements for systems actually installed in a building. As long as the incoming ground wire is landed at a point where there is bare metal (which it is) your panel is protected. As long as the screws that mount the chassis to the box are tight the ground connection to the chassis is solid.

The extra ground wire in the Fenwall panel could have something to do with the way the chassis mounts to the box. It is possible that the mounting system does not conduct a solid ground connection between the box and chassis, or the engineer wanted to be over the top on grounding the system. Just guessing on the reason for the extra wire. That is the reason for the box to door ground jumper. Otherwise the ground connection would depend on the hinge pin which is not sufficient.

I have a few panels that are chassis only (no box) that are just mounted to to a piece of plywood. I land the green wire to whatever screw on the chassis that is convenient. Nothing has happened to any of them.

It’s worthwhile to note that, while the chassis in the 4004 appears to be galvanized steel, the Fenwal 3220’s chassis has a black powder coat as seen in the photo. This coating could interfere with the chassis making a solid ground connection to the cabinet on its own, prompting the addition of a dedicated grounding lug.

There is the reason for the box to chassis wire.