Posted by Doug Root on May 02, 2016
1. Most common type sockets.
2. Typical wiring for
3. To confirm which type of socket is in the
Some shunted sockets may have 2 entries like the non-shunted socket. The contacts in shunted sockets connect directly at the socket so power moves from one contact to the other. Of note: the “shunt” may be internal to the socket and may not be view-able like in the picture above. Before installation you must confirm which type of socket is in the existing fluorescent fixture.
As a general rule in T8 fluorescent fixtures with instant start ballast have non-shunted sockets and in T12 fluorescent fixtures with rapid start ballast usually have shunted sockets. However use a voltage meter to test "continuity". If the two socket contacts show positive continuity, power flows between the contacts and the socket is shunted.
Shunted 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.
We call this type installations hard wired, ballast bypass or direct wire. The power is on one end No driver or ballast required, the driver is internally located inside of the plug and play or direct wire bypass tube light. After replacing the sockets one socket will have the live power feed as pictured in fig 2 and the other socket will serve solely as a lamp holder. NO power will be run to the other end.
The reason T8 LED requires non-shunted sockets is that the LED lamp is single end-powered. With shunted sockets, they work with fluorescent because you can utilize sockets on both ends of the fixture to complete the circuit. With LED you'd to put live AND neutral into the same side of the same socket, which would not work. With non-shunted sockets you can rewire and have 1 end live accepting the 120 or 277V circuit.
Pros – No need to replace
or maintain the ballast any longer.
Cons – Safety concerns over someone down the line putting in a fluorescent tube and it malfunctioning or possibly exploding due to the direct line current not being regulated through a ballast. Currently there is a sticker that installers are instructed to be apply at the time of the retrofit to alert that the wiring has been altered. This method is also labor intensive and may void the UL classification. Relabeling required.
*Power must be turned OFF. Must Be done by Electrician.
It is imperative that one understands the system they are working with when retrofitting a fluorescent system to an LED direct wire system. For those of you who want to simply go LED but do not want to hassle with the rewiring of the fixture then the "plug and play" option is the one you want. Read more about plug and play LED T8 lamps here.