Is it safe to convert a shunted tombstone lamp socket to a non-shunted socket by cutting the shunt?

Question

I am looking into converting a T-8 fluorescent tube fixture to a direct-wire LED tube fixture. In addition to removing the actual ballast, I understand that the "tombstone" lamp sockets in an electrical ballast fluorescent fixture are shunted, but for a direct wire LED tube, I should use non-shunted.

Based on the diagram in this vendor article: https://blog.1000bulbs.com/home/shunted-vs-non-shunted-lampholders it seems like it would be pretty easy to convert a shunted socket to a non-shunted socket with some wirecutters. Is this generally unsafe? And/or code-violating?

Answer 1

If you have replacement LED tubes that have a powered end and a dummy end you need non shunted tombstones. I converted a bunch of Lithonia fixtures from shunted to non shunted. Carefully remove the staple holding the tombstone cover. Remove brass clip holding no wire; remove wire from under other brass clip by lifting it with a thin nail or jewelers screwdriver. Then lift out the shunt and discard it. Find a drill bit the diameter of the copper wire and drill at least one additional hole on the side with no holes. Space the hole using the side with holes as a guide. For perfection, open up the fist 1/32 inch with a drill size that allows the wire insulation to just enter. If the clips do not grip the wire tightly bend them just enough to hold the wires tighter. Put the cover back on and press the staple back into its holes with appropriate small pliers. Strip wires about 3/8" before inserting. And reuse wiring that you took from the discarded ballast. If you have more than two tubes in the fixture, you will need to drill two holes in each tombstone not one. The tombstones at the dead end of LED tubes can be left alone, but clip off wires. Be sure to write notes on the fixture that explain what you have done and what tube to buy for future replacement.

Answer 2

You can't hack a shunted lampholder to be a non-shunted unless it's designed to do that. For one thing there is no place to attach the wires. Yes, there are two wire holes, but a non-shunted holder has four.

You have three options:

• stay with instant-start fluorescent... I am because the CRI is better
• change lampholders to non-shunted type
• take care to select LED "tubes" which take power from opposite ends of the tube

You should certainly not be modifying the wiring before you have seen the wiring diagram which comes with your LED tubes. You may find your tubes require a different wiring than what you did.

Answer 3

It actually is possible and not very difficult to hack a shunted tombstone and make it non-shunted. I got the idea when I was looking at purchasing non-shunted tombstones and noticed that in the description it said if you want it to be shunted just add some 18g wire between the two sides. So I opened up my shunted tombstones and noticed that they look exactly the same on both sides with a small clip in the middle. I took that clip out and now it's non-shunted.

It only has two holes for push in connection because it's shunted but the other side is exactly the same just without holes. So I took the clips out drilled two small holes and put the clips back in and closed the tombstone up. Now it's non-shunted with four push in connections. Two for black, two for white. I use all the leftover wires from the old wiring and it's exactly like buying a retrofit kit only I don't buy anything but lightbulbs.

Yes it's electrical and yes you are modifying it but if you just open the thing up and look at it, it's pretty simple to see how it works. Can you make one side of each tombstone all connect to power and the other side of each tombstone all connect to neutral with out anything connecting the two and without any wires that shouldn't touch touching each other? If the answer is yes, then you can do the job and it will work fine.

Answer 4

It really depends on the tombstones your light fixture came with. I did the LED retrofit for all the light fixtures in my plant, and some of the fixtures had tombstones that only had two holes on one side, some tombstones had only one hole on each side. I was able to modify a lot of the tombstones that originally came with the light fixtures, but there were a lot I wasn't able to modify either. Some tombstones were easy to modify by removing the shunt, but when I went to reassemble the tombstone it went back together feeling cheap and flimsy. But again there were a lot that I had absolutely no problem with. I had to retrofit well over 200 fixtures at my facility, some of them got new tombstones, some just reused the old ones. I would tell you to go ahead and try modifying your tombstones, and if they don't feel or seem to work right after you modify them, get some new tombstones online for $0.80 a piece.

The wiring below is for LEDs that have their own driver, so only one tombstone per bulb actually gets wired, and this is for an 8ft long 4 bulb fixture where power comes in from the center of the fixture. Power is supplied on the black and white wires that make contact on the opposite legs. This was mostly done as a joke for the other guys in my facility, but in the long run also shouldn't be a concern because, hopefully, the wiring will never have to be replaced anyway.

Answer 5

Glad you read our blog. We definitely agree that you should NOT cut into shunted lampholders for the reasons Harper stated above. Chris M. is also right. It's easier to just buy non-shunted lampholders, it will only cost you a few bucks. Since they are direct wire LED tubes, you only need to wire one side of the fixture.

Answer 6

All of the above answers miss the point. It's perfectly ok to modify shunted tombstones in order to connect double ended LED tubes - cut all wires entering the tombstone then wire them directly to either power or neutral, your choice. Make sure the opposite tombstone is neutral if other positive or the converse.

Make sure you really have a shunted tombstone. You can easily tell what you have with a multi-tester continuity check. Probe left and probe right but only when you have cut the wires away from the ballasts which might feed back to give the impression you are shunted - if it beeps you're shunted creating a problem for single ended tubes. Let me emphasize that I thought I had shunted but I didn't - checked continuity with wires still running to the ballast and it gave me continuity by looping back through the ballast. I actually took one tombstone apart and visually verified there was no bridge even though my meter originally showed continuity.

So now I'm rewiring for single-ended tubes. I will pull four tombstones (four tube fixture) on the side most convenient to incoming power. I have the two pin tombstones that snap in and don't rotate. To be elegant I will withdraw all wires (just twist and pull they'll come right out) then color match four of the same color to the left side of each tombstone (probably red for power) then four white to the right for neutral.

Both ballasts will be removed and all ballast wires cut away. I'll probably shorten or remove the incoming wires to the non-power side just to be tidy. When I'm done I'll have a power supply wire wire-nutted to the four red tombstone wires and the neutral wire wire-nutted to the four white tombstone wires. Your electricity may continue to another fixture so incoming power may be connected to that continuation wire. Some fixtures are grounded so do that just the way it was.

I'll post a picture when I get it done.

Answer 7

You can use shunted or non shunted tombstones but how you wire it will depend on whether the LED bulb is double ended powered or single ended powered.

If you are purchasing double ended powered bulbs you would connect power to one end (using shunted tombstone) and the opposite side (of the fixture) will be to neutral. If you have single ended powered bulbs, you need non shunted tombstones and would put power to one side of the tombstone and neutral on the other side of the same tombstone and only to one side of the fixture.

Connect all powered side wire to the incoming power to the fixture and all neutral wires to the neutral wire coming into the fixture.

For single sided bulbs, make sure you install the correct side of the bulb to the fixture. The bulb should indicate which side you should connect to the wired tombstone.

Most plug and play bulbs (using existing installed ballasts) are double ended powered bulbs. If you are taking out the ballasts and using the shunted tombstones, the wiring will need to be different. Power would go into one side of the tombstone and on the opposite side (of the fixture) would be neutral. Connect all power wire together to the power wire coming into the fixture and all neutral wires to the neutral wire coming into the fixture.