dont forget to clean tombstones

[junkhound]

GF calls and says her kitchen light goes off randomly, but will then also randomly come back on.

Whoops, know right off what it is, removed ballast from F96T12 fixture and wired for replacement direct 120V LED lamps. Forgot to hit the tombstones with wire brush before I left. 50 YO house.
Enough oxide on tombsiones to cause loss of contact at 120V, old F96T12 always got the 500+ V kick from the ballast.

 

[ramsy]

If burn marks are present would you allow tombstone replacement, per 110.12(B), or fire me for waisting time & money?

 

[domnic]

Enough oxide on tombsiones to cause loss of contact at 120V, old F96T12 always got the 500+ V kick from the ballast.

What is oxide on the tombsiones and how it could cause of contact at 120 v ?

 

[GoldDigger]

What is oxide on the tombsiones and how it could cause of contact at 120 v ?

The "tombstones" are the flat half-oval plastic (or at one time ceramic) pieces that hold the contacts which engage the pins on the ends of the tubes. Oxide on the spring steel or bronze of the contacts can form an insulating layer which prevents reliable contact with the pins.
The wiping action of inserting the tubes and rotating them will, at least temporarily break down the insulating layer. But with time and vibration the contact may be lost.
At 120V AC applied voltage the insulation layer may not break down, nor will there be arcing around the edges to restore the connection.

 

[zbang]

As someone who spent part of today touring an old cemetery, I had to think for a moment what this was about

 

[LarryFine]

A year or two ago, I rewired 85 3-tube troffers for LED tubes, reusing the original sockets and ballast wires. Every one worked and has continued to, as far as I know, with no cleaning.