LED T8 Retrofits With Internal Driver Require Non-Shunted Sockets

shunted versus non-shunted lamp socket diagram

If you choose T8 LED tubes with an internal driver as a replacement option for T8 fluorescent retrofits, you must be aware of an important issue relating to sockets.

Generally, an electrician completes this type of retrofit because of the re-wiring requirements. A critical step to be followed in the installation involves inspection of the existing G13 sockets (lampholders) to determine how the contacts in the socket function.

Shunted vs. Non-Shunted Lamp Sockets

Over 90% of all fluorescent fixtures use either of two socket types: shunted or non-shunted.120v-wiring

The contacts in shunted sockets connect directly at the socket so power moves from one contact to the other. It’s important to note that the “shunt” may be internal to the socket and invisible.

To confirm which type of socket is in the existing fluorescent fixture, a voltage meter should be set to “continuity”. If the two socket contacts show positive continuity, power flows between the contacts and the socket is shunted. These sockets must be replaced with non-shunted type for the LED retrofit to operate properly.  If there is no continuity across the contacts, the sockets are non-shunted and can be used with the LED tubes.

Why is this important? For LED tubes with internal drivers, the retrofit involves removing the existing ballast and rewiring the fixture  so 120V or 277V power connects directly to the socket.

If the socket is shunted, a dead short will blacken the socket and cause damage to the LED tube.

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Dave Burtner

Dave has been active in the lighting industry since 1994. Formerly a member of the Illuminating Engineering Society of North America and certified by the National Council On Qualifications for Lighting Professionals, Dave now writes blog posts, lighting tips and provides lighting product assistance for the Topbulb website.

17 thoughts on “LED T8 Retrofits With Internal Driver Require Non-Shunted Sockets

  1. Mr. Burtner,

    I work for a lighting products manufacturer and as a Marketing Manager one of many questions is get asked is the difference between shunted vs. non-shunted lamp holders. During my “google” search I came upon your description which was very simply stated. I wanted to check and make sure if it was ok you use your description in my documents? If yes will you please confirm at your earliest convenience. Thank you.


    Allen Guidry III, Marketing Manager
    Engineered Products Company

  2. Rich says:

    Hi Mr. Burtner,

    I’m a dealer for an LED tub that is universal. It works with the existing ballast, hard wired with shunted or non-shunted tombstones. They retail for $17.00 with a 10 year warranty. We are in the process of setting up our retail website. Should launch in the next couple weeks.


  3. Jeremy says:

    CAREFUL! Your annotation with the arrows saying “No Power between contacts” and “Power between contacts” are REVERSED. In a shunted tombstone the contacts are shorted together by the shunt, therefore there is NO power between the contacts. Perhaps you meant to say CONTINUITY rather then POWER?

    1. kenny says:

      I third that! Please review your pictures and labeling and correct them. It should say “CONTINUITY” for the shunted tombstone and “NO CONTINUITY” for the unshunted tombstone. “POWER” is incorrect and misleading.

  4. George says:

    Hi Dave,
    I would like to understand the difference in an LED tube driver that works with any ballast and one that does not work with any ballast.

    1. Dave says:

      Some LED tubes have internal drivers that are made to use the power provided by instant start ballasts and the shunted lampholders. This approach simplifies a retrofit by allowing an easy switch by maintenance staff from fluorescent tubes to LED.

      Other LED tubes have drivers that require a line voltage connection, in which case the ballast (instant, rapid or programmed) must be disconnected. The line voltage wiring is then re-wired to the LED driver usually requiring an electrician.

      The LED tubes that are “ballast compatible” are usually more expensive but the added product costs can be balanced against an easier, less expensive installation.

      1. Michael says:

        I currently have instant start ballasts with shunted connectors. I would like to bypass the ballast and wire directly. What kind of LED T8s do I need for this?


  5. Kelly Flowers says:

    There is a deeper and more dangerous issue here that few people are aware of. My comments here specifically apply to tubes which are intended to be directly connected to a 120vac source (or branch circuit in UL terms). The tombstone or lampholder MUST BE RATED FOR DIRECT CONNECTION TO A BRANCH CIRCUIT. MOST ARE NOT!!! As of this writing, I don’t believe Leviton has a single holder that is rated to connect to a branch circuit directly. IT IS NOT SUFFICIENT TO SAY THAT BECAUSE A HOLDER IS NON-SHUNTED AND RATED AT SAY 600v AND 600w, it can be used. I have found only 1 manufacturer of holders(Stucchi 3000 series of Italy) that has tested and, in writing, certifies it can be used for DIRECT CONNECTION TO A BRANCH CIRCUIT(although I’m sure there are others since folks are selling retrofit ‘kits’ that contain the tube, holders, and a label) Look at the installation sheet of ANY Leviton tombstone, and the 2nd bullet in the upper left hand corner states it’s not intended for connection to a branch circuit. [The technical reason is that an arcing and sparking hazard exists when the tube fails in a way that produces a partial for full short circuit and high currents are drawn through the tombstone contact where it touches the pin. There are also issues with the physical installation of the tube and exposure of ‘live’ contacts to the installer or the luminaire]

    Keep this in mind if you choose to do a retrofit using direct connect tubes, or if you hire a contractor to do it for you! You don’t want an accident in your facility number one, and secondly don’t want to find out that your insurer won’t cover you because you did not have the proper tombstone!

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