What is Ground?

We’ve all seen the familiar black GND terminals on MASSO controllers—tied to the negative terminal of the power supply. But here’s the thing: when people say “ground,” they often mean different things. So, what does ground actually mean in a CNC context?

Ground = A Circuit Reference Point

At its core, ground is simply a reference point in a circuit—often internal to a device. It’s what voltages are measured relative to. This reference is sometimes called common, and it can vary between systems:

• MASSO ground = Negative terminal of the power supply
• Gecko G320 ground = Positive common GND, incompatible with MASSO ground
• Shielding ground = Earth, not MASSO GND

This means that a single CNC machine may contain multiple grounds, depending on the devices connected.

Ground in Simple Terms

Let’s break it down with a simple circuit:

+ Power → Load (e.g. light) → Ground (−)

This loop works because the positive and negative create a complete path through the load.

Now add shielding for signal protection—like foil-wrapped cables. The purpose of shielding is to divert electrical noise (e.g. from motors, lightning, or static) away from the signal wires. But here’s the catch:

Noise always wants to go to Earth, not MASSO GND.

So, if you connect shielded cable to MASSO GND instead of Earth, you’re dumping the noise into 
your controller — the very thing you’re trying to protect.

Ground Isn’t One-Size-Fits-All

Just like vehicles, CNC systems use different grounding standards:

• Vintage cars used positive ground
• Modern vehicles use negative ground
• CNC machines may use positive or negative common (GND), depending on the device

So when someone says “connect it to ground,” they might mean:

• Earth ground(physical Earth, usually for shielding)
• Positive ground (e.g., +5V reference)
• Negative ground (e.g., 0V reference or power return)
• Chassis ground (connected to the machine frame)

Be specific. Don’t assume.

A Common CNC Mistake

Take this example:

“Connect the ground wire to the drive.”

But wait — what kind of ground is it?

If the manual said it’s a +5V ground drive, you’d connect it to the +5V terminal. If it said negative ground, you’d use the – terminal.

If you aren’t told which type, you don’t have enough information to wire it correctly. Always check the manual. If in doubt, ask.