Comparisons ·Feb 12, 2020

Shunted or Unshunted Tombstones?

Navigating the world of lighting often feels like learning a second language. With so many technical terms, finding the right components for your project can feel more like a chore than a DIY success.

One of the most common points of confusion involves shunted vs. unshunted tombstones. While they look similar, choosing the wrong one can lead to more than just a flickering bulb—it can cause serious electrical hazards.

Here is everything you need to know about these small but vital components.

What are Lighting Tombstones?

Tombstones, technically known as sockets or lamp holders, are the internal components of a fluorescent or LED fixture that hold the bulb in place.

Their job is to act as a bridge, connecting the electrical wiring of the fixture to the pins of the lamp. Because they are replaceable, you don't have to discard an entire fixture just because a socket has worn out. However, using the correct type is critical. Using the wrong tombstone can void your UL listing and lead to dangerous issues like:

Melted fixtures
Exploding lamps
Electrical fires

Shunted vs. Unshunted: The Core Difference

The easiest way to remember the difference is by the internal "pathway" of the electricity.

Shunted Tombstones (Joined)

A shunted tombstone features internally joined electrical contacts. This means there is only a single track for the electrical current to travel through. It receives the voltage and sends it through both pins of the lamp simultaneously.

Unshunted Tombstones (Not Joined)

An unshunted tombstone has separate points of entry (contacts). This creates two distinct tracks for the electrical current, allowing the electricity to travel to the pins independently.

Which One Do You Need?

The type of tombstone you need depends almost entirely on your ballast system or the type of LED conversion you are performing.

Use Shunted Tombstones for:

Instant Start Ballasts: Commonly found in standard T8 fluorescent fixtures.
Plug-and-Play (Type A) LEDs: These are designed to work with existing ballasts.

Use Unshunted Tombstones for:

Rapid Start or Programmed Start Ballasts: Often used in T5 fixtures or dimmable setups.
Direct Wire (Type B) LEDs: If you are bypassing the ballast to wire the sockets directly to the line voltage, you almost always need unshunted tombstones.
Magnetic Ballasts: Common in older "shop light" style fixtures.

Feature	Shunted	Unshunted
Contacts	Joined (1 Path)	Separate (2 Paths)
Common Ballast	Instant Start	Rapid / Programmed Start
LED Compatibility	Plug-and-Play (Type A)	Direct Wire (Type B)

Safety First

When upgrading to LED or replacing old fluorescent parts, always check the labels on your ballast or the installation manual for your new LED tubes. If you’re ever in doubt, reaching out to a certified lighting manufacturer or dealer can save you from a costly—and potentially dangerous—mistake.

Are you planning a fluorescent-to-LED retrofit? I can help you determine exactly which wiring diagram you should follow based on your bulb type!

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