Why Does My GFCI Trip When I Turn On The Light Switch?

Upgraded Home Team
by Upgraded Home Team

Ground Fault Circuit Interrupters, or GFCIs, are a necessary safety measure in modern times. They can prevent harmful ground faults that can cause dangerous and expensive electrical problems. So, why does my GFCI trip when I turn on the light switch?

Your GFCI will trip when you turn on a light switch if the neutral connection and ground are tied. The GFCI trips because it recognizes a drop in voltage that can be potentially dangerous as a safety precaution. If the light switch sends out 120 volts and gets nothing back, the GFCI will trip and shut off.

Never take it lightly if your GFCI trips when you turn on the light switch. Call a professional electrician if this happens so that they can diagnose the problem and repair it if necessary. Follow along as we explore why your GFCI trips when you turn on the light switch.

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Why Does My GFCI Trip When I Turn on the Light Switch?

A GFCI trips when you turn on the light switch if doesn’t receive the same voltage that it sends out. Many switches send out 120 volts, and they are supposed to receive 120 volts back. However, the GFCI will trip if it receives nothing back as a safety precaution.

This can also happen if the neutral connection is tied to the ground connection because that is dangerous. That can cause serious electrical problems and potentially start a fire if the GFCI doesn’t trip. A GFCI protects any switch or outlet connected to it and will trip if there is any inconsistency in voltage.

Any Ground Fault Circuit Interrupter on the same circuit as a switch or similar fixture will trip if there are voltage problems. GFCIs exist as a safety measure to interrupt a ground fault within 1/40 of a second.

What is the Point of a GFCI?

The primary purpose of a GCFI is to prevent electrocution. Every electrical outlet is designed to deliver and receive the same amount of voltage. If the hot wire (black wire) delivers 120 volts, then the neutral (white wire) must also send 120 volts back to the source. What if this doesn’t happen?

Suppose you have a corded skill saw. The cord is frayed, but you don’t notice the issue upon plugging in the tool. If you touch the hot wire in the cord, the electrical current will pass through you in its attempt to return to the ground.

If the tool is plugged into a GFCI, all you’ll receive is a small (but alarming) shock. The GFCI sensed that the neutral wire wasn’t carrying 120 volts back to the receptacle. As such, the GCFI opened the circuit in a fraction of a second, terminating the flow of electricity to both the tool and yourself.

GFCI Components

Ground Fault Circuit Interrupters consist of 5 simple components despite the advanced function. A GFCI can fail if any of the components come loose or suffer damage. That is why it is important to install them correctly or hire a professional electrician to avoid problems.

  • Two brass screw terminals on the right side for hot-wire connections.
  • Two silver screw terminals on the left side for neutral-wire connections.
  • One green screw terminal on the left side for a grounding connection.

The chief difference is that a GFCI has a “line” side and a “load” side. GFCI line sides are where you connect the incoming source of power. The load side is where you connect the outgoing source of power.

Importantly, the load side consists of the top two screws on either side of the GFCI (one brass and one silver). The line side consists of the bottom two screws on either side of the GCFI. Each component must be perfectly in line so that the GFCI can quickly trip in the event of a ground fault or voltage drop.

How To Install A GFCI

If you’ve installed a standard receptacle, you can probably install a GFCI. For simplicity’s sake, let’s say you want to connect a standard receptacle with a GFCI:

  • First, differentiate the cable serving the line end of the GFCI from the cable serving the load end of the GFCI. The line end will originate from the electrical panel.
  • Strip the sheathing from the cable and the insulation from the ends of all the wires. Cut the wires back if necessary.
  • Join the hot (black), neutral (white), and ground (bare copper) together in a pig tail. You should have two wires connected.
  • Take a bit of black, white, and ground wire, and tie them into the pig tails you made in the previous step, securing all three connections with wire nuts. 
  • Take the open ends of the third wires, and connect them to the appropriate terminals on the GFCI: bare copper goes to the ground connection below the GFCI’s plug, the neutral connects to the silver line end, and the hot connects to the brass line end.

What you’ve done is create a circuit in which the downstream standard receptacle is unprotected. Why? Because the load portion of the GFCI is not connected to the wires traveling to the standard receptacle. They’re just pigtailed together.

In the event that you do want to protect the standard receptacle with the GCFI, simply remove the wire nuts on the neutral and hot wires. Get rid of the third wires you used to connect the spliced wires to the GFCI, and connect the wires going to the second outlet to the load terminals on the GFCI. Simple as that.

Venturing into anything more complicated than this is definitely an electrician’s territory. Attention to detail is imperative. Especially if you’re using junction boxes to connect multiple fixtures and receptacles to a single GFCI.

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