Got a double 8ft T12 125wattflouresent fitting which try’s to strike but dosnt there are 2 ballasts Which Are wire wound and match the watts of the tubes, the starters also relate to 125watts but I’m unsure about the with rate at 7.5 UF is this enough ?
What’s wrong with this fitting and cap size
- Thread starter markymark2406
- Start date
If the tube flashes, the ballast is working.
If both tubes and starters are 125W types then it's either worn out tubes or broken starters.
100W tubes/starters will physically fit but will not work in a 125W fitting.
As 8ft tubes are virtually impossible to obtain now, it's probably time to replace the entire fitting anyway.
If both tubes and starters are 125W types then it's either worn out tubes or broken starters.
100W tubes/starters will physically fit but will not work in a 125W fitting.
As 8ft tubes are virtually impossible to obtain now, it's probably time to replace the entire fitting anyway.
?
capacitor is probably only PF correction so not relevant to your problem
If both ends of both tubes light up then it's the starters, if not, then more than likely the tubes
If both ends of both tubes light up then it's the starters, if not, then more than likely the tubes
8ft tubes often had 400 volt capacitors in series with the choke, when the cap fails the tube wont strike.
Taking the cap out of circuit usually gets the fitting working and verifies the capacitors knackered.
If it is for Power Factor its in Parallel with the supply cables
Taking the cap out of circuit usually gets the fitting working and verifies the capacitors knackered.
If it is for Power Factor its in Parallel with the supply cables
I honestly dont know, maybe some sort of boost to strike it, we used to take them out and the thing still worked.
Not to be confused with the ones fitted in series on twin fittings for anti strobing.
Been a long time since seen them, I dont recall how they built twin fittings as they never had 2 caps and an extra one for anti strobing.
Maybe the ops one Just has 1 for anti strobing
8fts were odd things some even had Two half chokes in to run one tube and also tubes in at least 3 different wattages.
Not to be confused with the ones fitted in series on twin fittings for anti strobing.
Been a long time since seen them, I dont recall how they built twin fittings as they never had 2 caps and an extra one for anti strobing.
Maybe the ops one Just has 1 for anti strobing
8fts were odd things some even had Two half chokes in to run one tube and also tubes in at least 3 different wattages.
Just checked an EC125 A140 choke was used with a 7.2 uF 440v capaciter,
EDIT
Found this on the internet
"The original British 8' tube was the 125W rating, and it was designed for use on an ordinary 125W high pressure mercury ballast with series capacitor, and of course a starter-switch. The series capacitor gave this circuit a leading power factor and provided a convenient method to easily strike this long lamp.
When the first krypton-filled energy saving tubes were introduced to replace the original Argon-filled T12 range, it was necessary to reduce the tube diameter to T8 size so as to maintain approximately the correct lamp voltage. This presented a difficulty for the 8' tubes because these were too fragile when manufactured in T8 glass. So for many years, there was no energy-saving alternative for the 8' 125W tube.
Around 1975, the problem was partially solved with Thorn's invention of the 8' 100W Krypton T12 tube. Filling the tube with krypton and keeping the diameter the same meant that the striking voltage was considerably increased. For any of the other plain choke-type circuits it would not have worked, but exclusively for the leading circuit with 125W MBF choke+series capacitor, the additional voltage spike delivered by the capacitor was enough to strike a T12 8' krypton tube. Owing to the fact that the voltage of this krypton tube is lower than its argon-filled predecessor, there was a reduction in lamp power from 125W to 100W, but only abut 9% drop in lumens. Hence it was a more efficient, energy-saving lamp.
Attempts to use a 100W tube on regular 125W or 85W gear without series capacitor do not work : the tube will not strike.
However some years later, since the 100W tube was becoming quite popular, a new dedicated 100W choke was introduced which didn't need the series capacitor, and if I understand the situation correctly, required a different glowbottle starter.
So in conclusion, if you have 125W gear and it is only the choke itself, then you will run into some difficulty in striking a 100W tube. But if you have the older 125W leading gear with series capacitor, then you can run either a 125W or 100W tube. If you have modern 100W gear then you can run of course a 100W tube and if you install a 125W tube, it will strike, but will be run a little below its design power."!
EDIT
Found this on the internet
"The original British 8' tube was the 125W rating, and it was designed for use on an ordinary 125W high pressure mercury ballast with series capacitor, and of course a starter-switch. The series capacitor gave this circuit a leading power factor and provided a convenient method to easily strike this long lamp.
When the first krypton-filled energy saving tubes were introduced to replace the original Argon-filled T12 range, it was necessary to reduce the tube diameter to T8 size so as to maintain approximately the correct lamp voltage. This presented a difficulty for the 8' tubes because these were too fragile when manufactured in T8 glass. So for many years, there was no energy-saving alternative for the 8' 125W tube.
Around 1975, the problem was partially solved with Thorn's invention of the 8' 100W Krypton T12 tube. Filling the tube with krypton and keeping the diameter the same meant that the striking voltage was considerably increased. For any of the other plain choke-type circuits it would not have worked, but exclusively for the leading circuit with 125W MBF choke+series capacitor, the additional voltage spike delivered by the capacitor was enough to strike a T12 8' krypton tube. Owing to the fact that the voltage of this krypton tube is lower than its argon-filled predecessor, there was a reduction in lamp power from 125W to 100W, but only abut 9% drop in lumens. Hence it was a more efficient, energy-saving lamp.
Attempts to use a 100W tube on regular 125W or 85W gear without series capacitor do not work : the tube will not strike.
However some years later, since the 100W tube was becoming quite popular, a new dedicated 100W choke was introduced which didn't need the series capacitor, and if I understand the situation correctly, required a different glowbottle starter.
So in conclusion, if you have 125W gear and it is only the choke itself, then you will run into some difficulty in striking a 100W tube. But if you have the older 125W leading gear with series capacitor, then you can run either a 125W or 100W tube. If you have modern 100W gear then you can run of course a 100W tube and if you install a 125W tube, it will strike, but will be run a little below its design power."!
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Nice to know you've learnt something new from me john, makes a change 
I learn something new nearly every day, and I'm sure it's not the first time I have learned/learnt (I don't know!) something from you - so thanks again!Nice to know you've learnt something new from me john, makes a change
Kind Regards, John
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