In short, "shunted" means "jumped". All T5/T8/T12 lamp holders have two pins. Some ballasts will treat these pins as individual pins, so the lamp holder must be "non-shunted", or just a normal lamp holder. These ballasts include obsolete magnetic and choke ballasts as well as modern program start ballasts. The picture shows a non-shunted lamp holder that has been manually shunted to connect the two pins together. In a pinch, this is fine. All non-shunted lamp holders will have FOUR wire holes, two per pin. Having two per pin allows for chaining the lamp holders together or shunting.

The lamp holder we use and sell are shunted. This means they only have two holes, both holes connect to both pins and the two pins are joined together inside the lamp holder. This is commonly done for instant start ballasts, which is the type we use for various technical reasons. They look like the lamp holder on the left, but with those two extra holes missing.

Program start ballasts send two discreet wires to each end of the lamp. (Most) instant start ballasts only send one wire to each end of the ballast.

Does it matter which you use?

Yes. If you are using a program start ballast and try to use shunted lamp holders, you will short out the ballast and may damage it. If you are using instant start ballasts and use a non-shunted lamp holder, you are only firing off one pin. It will work, but depending on the lamp internals, you may dramatically reduce lamp life.

For best service, always use the right type of lamp holder for the ballast you are using, or if you have to use a non-shunted lamp holder for an instant start ballast, be sure to manually jump the two sides.