2 wire polarized or 3 wire ?

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Old 09-10-20, 04:48 AM
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2 wire polarized or 3 wire ?

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?
 
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Old 09-10-20, 04:52 AM
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What do you mean when you say "cabinet"? Are you talking about an electrical enclosure or a storage cabinet?

All modern wiring should be 3 wire with 3 prong grounded outlets. 2 wire or two prong outlets are ancient history and exist because they are grandfathered.

As for your heater, wiring practices and requirements change over time. How your heater is wired can depend on it's age. Many products that are double insulated do not need to have their outer housing/enclosure grounded.
 
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Old 09-10-20, 08:26 PM
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Many products that are double insulated do not need to have their outer housing/enclosure grounded.
Dane stated it pretty well.

Keep in mind.... there is always a hot and neutral wire to every appliance. The white neutral wire will never be connected to the case. If the case is metal and should be grounded..... then there would be a three wire cord with a dedicated ground wire. If there is only a two wire power cord.... a ground is not needed.
 
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Old 09-22-20, 06:57 PM
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why are some two wire devises polarized?

Im not going to scrap this electric radiator type oil heater, but I do need to replace the plug.

pic below is NOT my specific device, but is example of electric radiator type oil heater.


 
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Old 09-22-20, 07:05 PM
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With some appliances or devices...... the manufacturer wants the neutral bus connected to neutral and the switched hot connected to hot. To expand...... in a typical appliance only the hot wire is broken or switched. The neutral is continuous. So based on the direction the plug is plugged in...... you may have always live inside the appliance and a switched neutral. A polarized plug insures that hot and neutral are connected correctly.


 
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Old 09-22-20, 07:15 PM
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tks. so i just need to see which wire is wired to the switch inside the unit and that should be hot.
 
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Old 09-22-20, 08:00 PM
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2 prong, non-grounded plugs are used only when there is no possibility of chaises become hot. Ie. plastic body or double insulated housing.
Neutral is never bonded to chaises because there is a possibility of it becoming hot and only allowed in some special cases (ie dryers and ovens).

Although body of oil radiator heater has metal chaises, all electrical components are contained without plastic housing in front and heating element is insulated from the chaises. Therefore, no need for ground.

Polarized plugs are used when polarity matters. Having a single pole switch on hot side only is one of those cases.

With polarized cord, wire with ribbing is neutral and smooth wire is hot. However, sometimes the manufacturer does not follow the rule. So, double checking is a good idea.
 
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Old 09-22-20, 08:13 PM
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pics





 
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Old 09-22-20, 08:19 PM
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It is hard to tell what is connected where from your picture, but the wire from the cord connected to the switch will be the hot wire.
 
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Old 09-23-20, 05:57 AM
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Hard to tell exactly, but that 2nd pix down looks hazardous. Those 1/4" right angle tabs look non-insulated and might be close to the metal heater element chassis ring???
What is the air clearance there?
 
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Old 09-23-20, 09:40 AM
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1/2" (The message you have entered is too short. Please lengthen your message to at least 25 characters.)
 
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Old 09-23-20, 09:46 AM
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another pic
 

Last edited by PJmax; 09-23-20 at 09:52 AM. Reason: labeled picture
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Old 09-23-20, 09:53 AM
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I labeled the neutral in your picture.
You can tell it's the neutral because you can see it's always connected to the heating element while the hot to the element is switched.
 
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Old 09-23-20, 10:23 AM
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so that is white large side of the plug?
 
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Old 09-23-20, 10:25 AM
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Yes..... that is correct.
 
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Old 09-23-20, 10:27 AM
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more pics


 
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Old 09-23-20, 10:31 AM
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More pics for what reason ?
 
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