Learning, Wiring,

What Happens If You Wire a Light Backwards?

In this article, ill be teaching you what happens if you were to wire a light backward.

Reversed polarity can cause lots of trouble. Sometimes, it might damage your electronics. Or sometimes, it can put you in harm’s way. Switching hot and neutral wires in a light bulb can cause similar issues. Knowing what these issues are will protect you and your home.

In general, even after you reverse the hot and neutral wires, the light will work just fine. But the issue lies in safety. Because of the reverse polarity, the current will flow backward and the light bulb’s steel cap is now connected to the hot wire. At this point, touching the cap can lead to electrocution.

We’ll go into more detail below.

Understanding How the Light Bulb Works?

To understand the reverse polarity issue, you should know about two parts of the bulb. Both of these parts are located on the base of the light bulb.

  • Electrical contact
  • Steel cap

Be mindful of: Here, I’m not going to talk about the filament, contact wire, and other parts of a bulb. Even though these parts are essential for a light bulb, we only focused on the parts that related to this post.

Electrical Contact

The electrical contact is the part located bottom of the base.

It is a round shape steel plate. This part is responsible for carrying the current from the wire to the filament. So, the bulb sockets are designed to connect the hot wire with the electrical contact. The black wire indicates the hot wire.

Steel Cap

Some recognize this part as the steel thread, and the bulb socket connects the neutral wire to the steel cap. The white wire indicates the neutral wire.

What Happens When I Reverse the Hot and Neutral Wires?

Imagine a situation in which you connect the hot wires to the steel cap and the neutral wire to the electrical contact.

The light bulb will work without any issues. But now the steel cap is hot. So, if you touch the steel cap while the power is still ON, you’ll get electrocuted.

Check the above image. The bulb with the correct polarity is on the left side, and the reverse polarity bulb is on the right. As I mentioned, both lights work fine.

What Happens If I Wire a Light Switch Backward?

neutral and hot wire diagram

Compared to a light bulb, wiring a light switch in the wrong way will lead to entirely different issues.

Despite that, if you know how the single or double pole switches work, you won’t wire them incorrectly.

For this demonstration, I’ll use a single pole switch as my example. The following should be true for a single pole switch wiring.

  • The hot wire connects to both poles.
  • The neutral wire connects to the breaker box for grounding purposes. It doesn’t go through the switch.
  • Some switches might have a green ground wire.

Because the hot wire connects to both poles, it doesn’t matter which side goes to which. But there are a few things that can go wrong.

What Could Go Wrong?

For instance, you might put the hot wire on one pole and the neutral wire on the other pole. This could lead to two different issues.

  • Such a connection might create a dead short circuit, and it will trip the breaker.
  • Or you’ll end up with an exploded switch and electrical fire.

How to Check for Incorrect Wiring?

For a light bulb or a switch, you now know what happens to them when the polarity is reversed. But, do you know how to check for incorrect wiring for a light bulb? (1)

For this, you’ll need the following things.

  • Digital Multimeter
  • Light bulb

After gathering the necessary things, follow these steps.

  1. Set the multimeter to AC voltage mode.
  2. Switch ON the light bulb.
  3. Connect the black probe to any ground connection.
  4. Connect the red probe to the light bulb’s steel cap. (2)
  5. The multimeter reading should be zero. If the multimeter shows a reading of 120V (close to), the wiring is incorrect.

Checking Reversed Polarity Outlets

To check reversed polarity outlets, use a non-contact voltage tester or an outlet tester. When you connect the outlet tester to the outlet, the indicator light will show up according to the wiring.

(1) polarity – https://www.britannica.com/science/polarity-chemistry
(2) steel – https://www.pbs.org/wgbh/americanexperience/features/

Video References

HanDIYman 007

Switchgear Training Classes

Everyday Home Repairs

The Engineering Mindset

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About Sam Orlovsky

AvatarCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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