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I sketched the following schematic from a motor controller board that has to be operated at 220V from L1 to L2. The earth wire is connected to the chassis of the machine.

Where I live, it's common to see ground and neutral at the same point for 110V machines.

My 220V connection has 3 wires: L1, L2, and neutral (not ground.)

That is, from L1/L2 to neutral I have 110V. What if I connect the earth point of the motor controller to the neutral point of my 220V outlet? I would have 110V between L1/L2 and earth and that means the neutral would be attached to the chassis. In this case, as I do not have ground on my 220V outlet, should I disconnect the chassis from the neutral?

enter image description here

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Using neutral as ground/earth is risky. In the event of a fault, you could be electrocuted.

When everything is working correctly, ground/earth and neutral are very close to each other in voltage. Close enough that you don't get any sort of shock if you touch neutral.

But sometimes neutral wires fail. They get corroded, or something damages them. At that point, the neutral-ground link may be lost. The neutral can then be at any voltage between 0V and your supply voltage, and it can vary unpredictably depending on what other appliances are turned on. If you have used the neutral as ground, this means that the case of your appliance can be at any voltage, and that voltage will vary over time.

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schematic

simulate this circuit – Schematic created using CircuitLab

Can you decide now, what you can or shall not do?

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  • \$\begingroup\$ I'm still kind of confused. I think I just shouldn't connect the outlet neutral to the equipment earth/ground. \$\endgroup\$
    – user115094
    Jan 10, 2019 at 16:28
  • \$\begingroup\$ Any Neutral fault currents such as arcing may induce such surges. It is normal to use Neutral only then ground the isolated frame only. \$\endgroup\$
    – Tony Stewart EE75
    Jan 10, 2019 at 16:34

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