Shunted Lampholders and Fluorescent Lights

If you have fluorescent lights in your home or business, you may have the need to change bulbs, do repairs, or even make upgrades. In order to understand things like shunted lampholders, it is vital to have an understanding of basic electricity and fluorescent lighting first. Let’s check out the basics, so you can be doing your own work soon, and safely.

How Electricity Works

If you look at a light fixture you may see three colors of wires, black, white, and green (or bare). To simplify how electricity works, power comes in to the appliance on the black wire, is used and leaves on the white wire, where it is neutralized into the ground. The black wire is often to referred to as the “hot” conductor and the white is “neutral” or “grounded”. So where does the green wire come in?

You will see green wires connected to the metal chassis of appliances. This is for safety reasons. The green wire is the grounding conductor and effectively grounds the appliance to prevent shock hazards. Should the black conductor come in direct contact with the white or green conductor, this will create a short circuit and can result in burning or even fires. However, circuit breakers and fuses are designed to take care of this problem by automatically killing power to the overloaded circuit.

Fluorescent Lights

Fluorescent lighting works on the principle or applying electricity to gas and the burning gas creates light. Bulbs contain gas and are sealed and electrodes are inserted into the bulbs. Bulbs are placed in lampholders (sockets) to receive the power they need to light and these holders can be non-shunted or shunted lampholders.

Not long ago lamp sockets were made to allow power to pass through the bulbs in the circuit. This creates a “series” connection and when one bulb burns out the entire circuit is dead.

A shunted lampholder or socket has a connection between both leads. This creates a parallel circuit and once a bulb burns out, the other bulbs in the circuit will stay lit.


Fluorescent lights do not work on standard 120 volt current. They need much higher voltage and this is supplied by ballasts, which act as transformers. If you ever uncertain as to whether you have non shunted or shunted lampholders, it is very easy to find out. Run a continuity check across the leads. You will have continuity if the socket is shunted and nothing if it is a non shunted socket.

Always make sure to turn off the circuit breaker and check for power before working on electric lights, and use the right type of bulbs for your fixture. If you are unsure what you are doing, let a qualified electrician take care of the job.

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