t=8 lamp problems

Merry Christmas
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I have several sidemount single lamp t-8 that are burning/melting the tombstones on one side of the fixture.
any help is appreciated
 

mdshunk

Senior Member
Location
Right here.
Seems to be a common problem that people are reporting, but I've never seen it myself. The cure seems to be to replace the tombstones with a different brand, and all is well. The suspected culprit is poor lamp pin contact by the original tombstone.

I wonder if the lamp filament current is that much higher with T8's versus the former T12's?
 

HighWirey

Senior Member
"I wonder if the lamp filament current is that much higher with T8's versus the former T12's"

Marc,
I didn't think any filament current flowed between the pins on the same end of a T-8. (both pins on a bi pin lamp holder are connected together somewhere in the circuit. Only current flowing through each tombstone is from one end of the lamp to the opposite end, even then what little bit of current flows from lamp end to end is somewhat shared between both the same end tombstone’s pins.
The total line current for a Sylvania Quicktronic 4 lamp 32 watt T-8 ballast is .95 amp at 120 volts.

Don’t know if I can subscribe to the too much current idea. I do not doubt that many tombstones are melting in the field though.

Help anyone?

Happy New Year Everyone and Best Wishes
 

iwire

Moderator
Staff member
Location
Massachusetts
HighWirey said:
(both pins on a bi pin lamp holder are connected together somewhere in the circuit.

Not with most T-8s, that is why many times when converting a fixture from T-12 to T-8 the shunted tombstones must be replaced. :smile:

IMO T-8 lamps run much warmer then T-12s and that may contribute to tombstone melting.
 

peter d

Senior Member
Location
New England
Actually, I've caused a meltdown recently when replacing some T-8 lamps. The fixture was made for T-8 lamps so it had the correct lampholders.

I didn't seat one of the lamps all the way, and the next thing I know the lampholder is actually on fire with smoke pouring out and quickly melting down. I didn't know that T-8 lamps had that much current going through them.

I took the lamp out before the lampholder was completely destroyed, but it was an eye-opener to say the least.
 

HighWirey

Senior Member
iwire,

I'm looking at a Sylavnia 4 lamp, and a Motorola 2 lamp T-8 ballast. According to the label on both ballasts, both pins of each end of their T-8s are connected together.

Put a clamp on the lamp leads on the Motorola, zero current was indicated, I suspect due to the 20-30 khz operating frequency.
Also checked the temp on two 32 watt T-8 lamps which had veen operating for several hours, highest temp observed was 90F. I have seen those real hot ones though.

A poster on another forum was having a big problem with melted tombstones. He posted "I sent US Energy Sciences some of the tomb stones. They replied on 12-5-07 that the tomb stones were fine They are saying that possibly the bulbs are not seated properly or the new tomb stones do not line up correctly" Havent heard back from him.

Sure would like to know the real cause of the problem. Can't be much left besides seating of the tubes?

Happy New Year and Best Wishes
 

mdshunk

Senior Member
Location
Right here.
HighWirey said:
Sure would like to know the real cause of the problem. Can't be much left besides seating of the tubes?
Probably so, but I do know that some tombstone designs lend themselves to proper seating of the lamp pins more easily than others. Some you really have to look at closely to make sure that you've got the lamp engaged the whole way.

A lampholder that will otherwise make good contact but is difficult to use as intended in the field is of no real value.
 

iwire

Moderator
Staff member
Location
Massachusetts
HighWirey said:
iwire,

I'm looking at a Sylvania 4 lamp, and a Motorola 2 lamp T-8 ballast. According to the label on both ballasts, both pins of each end of their T-8s are connected together.

Different models. :)

I have installed 100s of Sylvania ballasts and they all needed the shunted sockets replaced with non-shunted sockets.

Check out the second page of this pdf cut sheet for the ballasts we use, you can see the circuits to the tombstones are not connected together.

SYLVANIA QUICKTRONIC
 

HighWirey

Senior Member
I can't get this link to work says page can't be displayed"

HighWirey couldn't make it work, either. This one works, though:
ecom.mysylvania.com/miniapps/product/PIBs/ebcat1099.pdf

Never used those long, white, skinney Quicktronics, but they are wired like a conventional ballast (series/parallel version). I only bought the 4 lamp parallel version Quicktronics ballasts, could use em on two, three or four lamp fixtures, very little price difference.

Happy New Year Everyone and Best Wishes
 

HighWirey

Senior Member
Dennis,
Your 'Take Two' link was good.

Don't want to beat a dead horse but some contractors need help on this.

Spoke to my EE brother about the melting tombstone problem. Many of his designs have received UL approval, and he is very conversant with UL. He said that one of UL’s many electrical approval criterium is something called "Contamination Index'. This index deals with many factors, such as material, spacing, and contamination (at the time of item manufacture). Additional contamination after the install would only exacerbate an older, possibly marginally designed keystone.

He suggested that one end of a T-8 is closer to ‘return’ potential than is the other end, and the ‘hot’ end should be prone to heating first, especially at 20-30 khz, with maybe 1 kv, or more, applied during lamp start up. So it seems that it is not the current, but the voltage.

Early on KB Sparky, on another forum, suggested that high freq was the problem, I was not sharp enough to pick up on that.

Better explaination anyone?

Only advice here is to factor in some fat on your bid. I know, fat can cause you to lose a project, but what is the worse of the two weevils?

Till then, keep changing those tombstones out . . .

Happy New Year Everyone and Best Wishes
 
melting tombstones

melting tombstones

Thanks very much for all replies,
I am going by the restaurant in the a.m. to check on them.

I had changed out one tombstone prior on the first melt (this one had melted 2's so far)

I replaced the whole light the 3rd time and changed the lamps. (lamps are no 741's were originally 841's) just looking for any possibility

seems as though the tombstones are all melting on the right( w/ fixture in front)

I dont paticularly care for the way that lamps sit. (tombstones and mounting dont seem rigid enough to remain straight)

the fixtures are made by symkar(single lamp side mount
thanks again
 
just for some final thoughts.... went back and 3 of 4 are a.ok
4th one was de-energized from last trip

I changed one fixture out completely and tombstones on the other two. also changed lamps from 841 to 741 's

I wish i could say that i repaired the problem and understood why.

thanks again
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
electricjireh said:
I wish i could say that i repaired the problem and understood why.
Well, one out of two ain't bad. :rolleyes: ;)

Look at it this way: you're learning stuff. :smile:
 
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