As we often mention on this blog, lighting is complex.
Shunted and non-shunted sockets, or tombstones, is one of those topics that seems to scare off a lot of our customers. They don't want to touch it with a 10-foot pole.
But we're here to quell your fears. There's an easy way to know the difference between shunted and non-shunted sockets and when you need which. And we're here to make lighting –– and sockets –– easy.
Do you know what kind of sockets you need?
Knowing which sockets you need for your linear lamps is hugely important. Using the wrong type can not only void the UL listing on your lamp
In this post, we will share some guidelines for telling the difference between shunted and non-shunted lamp holders and when you should use which.
Telling the difference between shunted and non-shunted sockets
When you hear the word "shunted," think "joined" or "connected." Shunted sockets feature internally connected electrical contacts. This provides a single track for the electrical current to travel from the ballast, through the tombstone, or socket, and to the lamp's pins.
Non-shunted sockets have separate contacts –– or points of entry for the wires –– creating two tracks for the electrical current to travel. Non-shunted sockets have contacts that are not joined/ connected.
The diagram below visually demonstrates the difference you'll most often see between the two types of sockets.
Because there are exceptions to this visual difference, however, the safest, most certain way to figure out what kind of sockets you have is to use a voltage meter. Most voltage meters will either light up or ring or beep if the electrical contacts are connected, or shunted.
As you can see above, shunted sockets receive voltage through a single set of wires and spread it to two contacts. Non-shunted sockets, meanwhile, send voltage to each of the contacts, through two wiring tracks.
When to use shunted sockets and when to use non-shunted sockets
Now that you understand how shunted and non-shunted tombstones work and how they are different, here's the information you've been waiting for: when to use which type.
Please note: the table below is meant to reflect broad-sweeping general recommendations for socket pairings, but there are exceptions. For example, there are T8 plug-and-play LEDs made to work with rapid-start ballasts and programmed-start ballasts, requiring non-shunted sockets. Always double check with your lighting specialist or the lamp manufacturer to know what sockets you need.
Bi-pin lamp type
Shunted or non-shunted?
|T8 with rapid-start, programmed-start, or dimming ballast||Non-shunted|
|T8 with instant-start ballast||Shunted/
*Non-shunted (with external wire shunt)
|T5 with rapid-start, programmed-start, or dimming ballast||Non-shunted|
|T5 with instant-start ballast||Shunted|
|T8 direct wire
|T8 remote driver||Non-shunted|
|T8 with magnetic ballast||Non-shunted|
*There is the option to externally shunt a non-shunted socket with wires if you're looking to
We have mentioned why it's so important to purchase the right sockets. There is quite a bit of risk involved.
If you have any questions, as always, don't hesitate to speak with your lighting specialist. Whether you're completely lost in the complexity of sockets or you just need a gut check, we're here to help.