Metal case requires grounding?

[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?

 

[rnatalie]

Generally, exposed metal needs to be connected to the equipment grounding conductor, not to a neutral or common. There are certain grandfathered cases (stoves, dryers) that allow the grounded conductor (i.e., the neutral) to be used. Grounded conductors are not preferred for grounding safety as they are carrying current and the resistance of the conductors may place them at a different potential than the actual ground and may also not provide the minimal impedance path that a dedicated EGC would.

Certain appliances don't need grounds if the exposed parts are unlikely to become electrified (double insulated). That's more of a listing (UL, among others) than an electrical code issue.

If you want to put a three-wire cord and plug on the thing, and connect the case to the EGC the case, that might be reasonable. You do not want to just go willy nilly connecting a current-carrying wire (at any potential) to the case for the above (and other) reasons.

 

[petersonra]

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?

If it is a relatively modern appliance with a metal case, it is likely the metal case would be connected to the EGC of the power cord. Some older (much older usually) metal cased appliances did not do so.

If it is plastic cased it is likely double insulated and thus does not require an EGC.

In any case, the neutral wire in the power cord should never be bonded to the metal case with a few exceptions such as some older ranges.

Personally, i would likely just replace an old space heater like this. it is probably not worth fixing.

 

[tom baker]

To the OP, are you a DIYer? As pointed out, not worth the time, and may not be safe to fix. Your questions indicate a lack oe electrical knowledge.