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have a question on wiring an LED (backlit) mirror.

So we purchased a LED backlit mirror and I started prepping to wire it to the wall, planning to hardwire it. The mirror came with a plug and recommendation to cut the plug and use corresponding wires to hardwire.

The way it works: line voltage comes in, goes to LED driver that transforms that to 12V that is connected to LED strips around the backing of the mirror.

To ensure that I'm using the right polarity I opened up the box with the LED driver and found this: LED driver wiring in backlit mirror

This is how it was wired out of the box. See the diagram next to the ports. So:

  • Unless I'm missing something here, Hot(Line) wire is connected to where Neutral is supposed to be and Neutral is connected to where Line is supposed to be - reversed polarity on that connection.
  • The mirror actually works - don't know if that's normal for these LED drivers to work with reverse polarity connected.
  • I checked the output on the other side - it outputs 12V DC with the correct polarity as depicted on the diagram.
  • I'm guessing this was mis-wired at the factory. We purchased 2 of these with different orders and they came same way, so I guess there's also a chance that this was a bad batch of LED drivers that the manufacturer knew to connect like this.

Manufacturer customer support is not helpful.

Questions:

  • First let me know if I'm understanding this wrong.
  • Is it normal for LED drivers to still work when reverse polarity connected?
  • Would it make sense to attempt connecting it the right way and what are the risks of doing so?

I'll need to make this work with this type of mirror as we don't have much alternatives - seems like I have following options:

  • a) Hardwire into the wall the way this is now, with what seems to me like reverse polarity.
  • b) Try to wire this properly and, if works - hardwire properly in the wall.
  • c) Purchase another LED driver with good reviews and wire it according to the specification. What would you do?
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Fixtures must be UL/CSA/ETL listed

I see the driver module is RU Recognized (with a file number... that means it is UL-Recognized as a component. But is the entire fixture UL Listed? If the fixture is not UL/CSA/ETL listed, you can't use it in North America. El NEC, 110.2, and CEC.

Since I hear the word "order" and "reviews", I gather this is mail-order. Don't buy electrical equipment mail-order. All the major "online" sites allow "third party sellers", often without making that point clear. These channels are flooded with slickly marketed but cheap foreign crud that will kill you. They usually say "CE", which is faked. Get your money back, don't let them profit!

The idea of the fixture not being UL listed is particularly terrifying when it is made of plastic, since plastics are made of petroleum! Any random plastic will burn viciously, and will emit poisonous gases that will incapacitate you in your sleep... unless they are made of much more expensive plastics with even more expensive modifiers to make them resist burning and self-extinguish if lit externally. There's a whole chapter in the UL White Book just for that.

Needless to say, fakers don't use the right plastics.

Polarization on the AC side does a different job

On the DC side, polarization is to make the device work. The electrons won't go through the semiconductors right if they're reversed. On the AC side, polarization is about safety.

Current flows in loops, so the AC supply has 2 active conductors. Stuff fails. One failure mode is "connect one of the AC supply wires to something the user might touch". On most equipment that's more likely to happen with one AC wire than the other. This is enhanced further by intentional design - deliberately making such a failure far more likely to happen with one AC wire than the other.

Most AC design (not Philippines) has one of the two AC wires intentionally bonded to near earth voltage, so if everything is working, that wire is mostly harmless. That wire is called Neutral. You see where this is going: Polarization is about making sure the "likely wire" is neutral.

However, belt and suspenders, that particular drive module is also double insulated - meaning such leakage could only happen with two things failing. Note the "square in square" icon coexisting with an RU icon with file number, meaning UL has approved the component as double-insulated.

So it's possible that in light of the double insulation, UL has given them a pass on the reversed wires. Or the UL inspector wasn't around while they trained up a new employee.

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