Shunted or Unshunted Tombstones?

When looking at lighting, it may seem like there are tons of options on the market, and each one has unique characteristics. Finding the right solution for your needs can feel like homework. One of the most commonly confused matters is the one regarding shunted or unshunted tombstones. If you are unclear on the differences between the two types, or which one your lighting project needs, there are a few things to know about these small components. Let’s take a closer look at this matter.

What are they?

Tombstones, also sometimes called sockets, are small internal components of a fluorescent or LED fixture. They are responsible for connecting the electrical wires from one end of the fixture to the other and receiving the current of electricity which powers the lamp into creating illumination. If they stop working, they can be replaced instead of replacing the entire fixture which makes them an integral concept of lighting to understand. Aside from making sure they are working properly, you also need to make sure you use the right one in regard to shunted or unshunted tombstones. If you use the wrong one, it can void the UL listing on the fixture. It can also lead to potentially costly and dangerous electrical shortage issues such as melted fixtures, exploding lamps, and even fires.

How to Tell the Difference Between Shunted vs. Unshunted

A great way of thinking about shunted is to remember it as joined and unshunted as not joined. Shunted tombstones have two joined electrical contacts internally which allows you to create a single track for the electrical current. An unshunted tombstone has separate points of entry, or contacts, for the wires which will create two tracks for the electrical current. So, how do you know which type of tombstone is right for your fixture? In general, it will depend on the ballast system in place. For example, if you are operating a fluorescent fixture T5 or T8, you will need a shunted tombstone. When working with a T5 or T8 fixture operating under a rapid start, dimming, or programmed start ballast, you will need an unshunted. When looking at LED lamps, you will need shunted tombstones only for plug-and-play ballasts. Unshunted is recommended for LED fixtures operating under magnetic ballast, remote driver, or direct wire operations. Of course, if you have any questions, you can reach out to a lighting manufacturer or lighting dealer for assistance.