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LED T8 Retrofits With Internal Driver Require Non-Shunted Sockets

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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.

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.


But SEPICN LED Lighting UL Type A+B led tube lights could be working with Non-Shunted or Shunted sockets both.