Shunted vs. Non-Shunted Sockets
January 9, 2025
There are many socket options available in the lighting market, and consumers often wonder whether to choose shunted or non-shunted sockets. Selecting the correct sockets for a linear lamp is paramount to prevent hazards such as electrical shorts or compromised safety.
Using the wrong socket type could lead to a fire hazard, causing damage to both the tubes and sockets or, in the worst-case scenario, endangering lives. Moreover, using the incorrect sockets might void the UL listing on the lamp or reduce its overall lifespan.
This post will delve into the differences between shunted and non-shunted sockets and help you to understand when to deploy each.
Differentiating Shunted and Non-Shunted Socket
It is easy to recognize shunted and non-shunted sockets if you understand how they work.
For shunted sockets, electrical contacts feature internal connections, creating a single track for the current to travel from the ballast through the socket (or tombstone) to the lamp’s pins.
Non-shunted socket provides separate contacts, allowing for multiple entry points for wires and creating dual tracks for the current to travel.
Visually, this distinction is apparent, but exceptions exist. To get an accurate result, use a voltage meter, which will react when contacts in shunted sockets. Do not forget to set the voltage meter to “continuity” mode.
Shunted sockets distribute voltage using a single pair of wires, connecting it to two internal contacts. In contrast, non-shunted sockets deliver voltage independently to each contact via a separate wiring path.
When to Choose Shunted vs. Non-Shunted Tombstones
Understanding the basics of how these sockets function makes it easier to determine when each is needed for your lighting requirements. While numerous tables and charts outline specific examples, the choice often hinges on the ballast used for the fixture.
For fluorescent lights, the majority require a non-shunted design, with instant-start ballasts being the only exceptions. T8 fluorescent lamps, however, can be non-shunted instead of shunted with an external wire.
Many LED designs are compatible with both shunted and non-shunted tombstones. Plug-and-play products may require shunted sockets, while most others, especially those using ballast bypass, are compatible with non-shunted sockets.
If uncertainty lingers, seek advice from a local lighting specialist to ensure the right sockets are chosen, mitigating potential risks.
