Metal cabinet requires polarised plug

[paulmars]

My understanding is that metal cabinet needs to be grounded to the common or neutral 3 wire.

Questions:

When is 3 wire required and when 2?

Why are some plastic cabinets polarized 2 wire or 3 wire?

Why is this metal cabinet space heater that im try to fix, why its 2 wire and neither is common grounded to its metal cabinet?

 

[paulmars]

pictures attached

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[Megawatt]

My understanding is that metal cabinet needs to be grounded to the common or neutral 3 wire.

Questions:

When is 3 wire required and when 2?

Why are some plastic cabinets polarized 2 wire or 3 wire?

Why is this metal cabinet space heater that im try to fix, why its 2 wire and neither is common grounded to its metal cabinet?

Paul the best way I can explain polarized is take a lamp with a screw in bulb and the neutral terminates to the part that you screw in the bulb and the hot wire terminates on the tip If you cross the wires then you just made the screw in part hot. It’s all about the manufacturing company and how it’s internally wired. No plastic doesn’t need grounding and metal cabinets does. Since your working on this if it has 2 wires you need to leave it that way.