The mystery of the intermittent fault on flourescent light

[The Ghost]

So I was called again to look at light in unit that has gone off. Of course when I got there it was on (again) The circuit is very straight forward, supply from Merlin Gerin DB 10a MCB supplying four twins. Checked all the connections for being tight including switch (wiggled and pulled) and securely fixed into termination points, all ok. Checked cable down to light from klix rose, ok. The fitting is HF with TriPhos tubes. The light stays on during this process no flicker.
So I have checked the cabling from the MCB to first light (which is the one with intermittent fault) and checked onward to the last light, four in all. No loose connections, all lights are working except this one, occasionally does not. As you may divine from the picture below it is not a situation (20 feet up) that lends itself to popping up with a tester and having investigations without a tower which is considerable expense. The cable (singles) is in plastic trunking changing to 20mm conduit as it progresses to each light. There is no sign of damage to the cables I can access, and have fought shy of putting up a tower due to cost and the landlord being a very very frugal person to put it charitably. Any ideas of a brilliant nature welcome.

 

[ruston]

Are the end caps ok , those lights may require both lamps working. one out both out.

 

[Wilko]

Starter is no longer starting reliably would be my thought. But you probably have already replaced starter and tube?
Or go straight to one of these perhaps?
5ft 24w LED Fluorescent Tube - Cool White - https://www.tlc-direct.co.uk/Products/LTT524CW.html

 

[ruston]

It should not have a starter if it is HF.

 

[Deleted member 104825]

Do HF fittings suffer in the cold like ordinary fluo's?
I had an ordinary fluo in my garage that hated the cold and when I swapped it with an identical one used in the house then both worked fine - they both came from same supplier, on the same day, and fitted on the same day - so identical except one was a wuss!

 

[The Ghost]

Are the end caps ok

New fitting and tubes. Not an end cap problem

Starter is no longer starting

Ooops no starters in HF.

 

[KEV 1 N]

Could be a dodgy lamp, does the fitting have one ballast for both lamps or one each? Most likely dodgy lamp or ballast.
I put a new HF flossy fitting (came with new lamp) in my dads garage a while ago, soon after he said the light would either not light or just flash then go off, put in a new lamp and had no bother since.

 

[The Ghost]

Could be a dodgy lamp

This intermittent problem existed with previous lamp so doubt new lamp is dodgy, possible but not likely I guess.

 

[Jim90]

Replace the ballast. 6ft will have a PC2/70W and a 5 foot will have a PC2/58W. Some of the bigger wholesalers stock them too. Would be easier to do that off your ladder than the whole fitting! If it's non EM might be worth putting LED tubes instead. Less to go wrong.

 

[marconi]

A few questions please:

a. Does the fitting sometimes not illuminate when first energised and stay off? Or does it later illuminate?
b. Does the fitting sometimes illuminate immediately and later go off and stay off?
c. Is the fitting bathed in warm sunshine? The picture seems to show skylights in the corrugated roof.
d. At the first fitting at the end of the drop what is the L-N voltage before and after turning these lights on?
e. Any high amperage loads on the phase?
f. At any time is the fitting operating outside its designed temperature range? ie: first thing in the morning unit is cold.
g. Has the drop to the fitting been clamped excessively tightly deforming the live conductors? (I discovered this once on my wife's iron plug - an MK screwless clamp).
h. Is the Klix rose faulty? Change it if a check shows it is plugged in correctly.
i. Is there anyway someone could be playing mischief with the fitting or Klix rose.
j. Are the four fittings wired as a daisy chain or otherwise?
k. Is is a type B or C mcb?
l. what is the length of the run from mcb to first fitting and what is the guage of the live conductors?
m. Could you swap over complete fittings say 1 and 2 and see if the intermittent illumination moves with the fitting?

 

[Spud28]

we had a batch with faulty ballasts try swapping for new or from a known working fitting

 

[westward10]

Get suitable access equipment before you end up in hospital or the morgue.

 

[marconi]

https://www.tlc-direct.co.uk/Technical/DataSheets/Lighting/HF.pdf

Have the correct tubes been installed in the fitting? I turned up this reference which has some advice on lamp compatibility.

I also learned that some fittings have switches in the end caps as a safety feature to isolate the contacts when no tube is present.

This reference-

Appendix B: Ambient Temperature and Atmospheric Conditions | Universal Lighting Technologies - https://unvlt.com/literature/troubleshooting/linear-fluorescent-lighting-systems-maintenance-guide/appendix-b-ambient-temperature-and-atmospheric-conditions.html

talks about the deleterious effect of low temperature on the ability of a ballast to start and run a fluorescent tube and also what happens when tubes do not reach their designed operating temperature.

 

[Zdb]

Change the ballast or whole fitting. Simples .

 

[Deleted member 72666]

Electronic ballast is the likely culprit.

 

[marconi]

I remember that the very early tubes had an earthed conductive strip along their length to aid starting. I suppose the same capacitive effect is achieved now by internal coatings and the proximity of the tube to its earthed fitting. So check too the connection of the cpc to the fitting, the continuity of the cpc back to the DB and that the reflector is electrically connected to the cpc.

 

[Jim90]

Tad overkill for the one light?
Remember that this bloke is connected to the steel structure on a metal ladder and (within our firm) has to maintain three points of contact on said ladder. Throw a loop test into the mix and a RCD protected circuit then we're in for a show!

 

[The Ghost]

a. Does the fitting sometimes not illuminate when first energised and stay off? Or does it later illuminate?

No it works for 3 months the goes off for a few hours and comes back on totally at random. Then goes off after a few more months and goes back on in a few days etc.

b. Does the fitting sometimes illuminate immediately and later go off and stay off?

No See a.

c. Is the fitting bathed in warm sunshine? The picture seems to show skylights in the corrugated roof.

No it is not in any sunshine.

d. At the first fitting at the end of the drop what is the L-N voltage before and after turning these lights on?

Same, 246v

e. Any high amperage loads on the phase?

No there are no high A. equipment it is a kitchen with gas stove.

f. At any time is the fitting operating outside its designed temperature range? ie: first thing in the morning unit is cold.

No the unit has central heating which keeps the temperature ambient

g. Has the drop to the fitting been clamped excessively tightly deforming the live conductors? (I discovered this once on my wife's iron plug - an MK screwless clamp).

No there is no mechanical damage to any part of the lighting installation

h. Is the Klix rose faulty? Change it if a check shows it is plugged in correctly.

That is the only thing that has not been changed and thought to do that next.

i. Is there anyway someone could be playing mischief with the fitting or Klix rose.

Not a chance

j. Are the four fittings wired as a daisy chain or otherwise?

Daisy chained one after the other

k. Is is a type B or C mcb?

Type B

l. what is the length of the run from mcb to first fitting and what is the guage of the live conductors?

1.5mm² 7 m.

m. Could you swap over complete fittings say 1 and 2 and see if the intermittent illumination moves with the fitting?

A lot more trouble than it is worth, might as well rewire it if I am going that far

 

[The Ghost]

reflector is electrically connected to the cpc.

This whole complex has recently had an EICR including this unit and it has been checked and passed I have read the results of all of it and this unit has R1 R2 plus Zs all ok.

 

[Lucien Nunes]

Unlike a choke, which is simple and usually either works or doesn't, an HF ballast is an electronic switched mode power supply, containing many dozens of components (some of which have finite lifespan) and connections. Intermittent faults are not only possible but likely. If the lamp is new and good and the endcaps undamaged, I would have changed it by now.