Fluorescent lights

[copey84]

Afternoon all, have had complaints about failure of fluorescent lights control gear.
Done all tests on circuits and all ok, only problem I can think of is there is a mix of magnetic and h.f ballasts on both circuits that have failing fittings. Is this a possible cause of reduced fitting life?
Both circuits are wired in twin and earth from a 3phase d/B, TT installation, only 9years old and have replaced about a dozen fittings two in particular that go more often.
Each circuit has 12 fittings that range from 2D to 5ft fluorescent, there are also emergency exit boxes that have also quit and non maintained bulkheads, one of which has failed and been replaced.
Not sure what's going on, seems to be going through to many fittings for my liking.
Appreciate any replys, thanks.

 

[Deleted member 72666]

I would also check between neutral and earth. Btw what's the earthing arrangement?

 

[copey84]

It's a TT earthing system, tncs is available at cut out but not in use because regs for filling station doesn't allow it's use.

 

[copey84]

The failed light turned out to be a h.f fitting only in 6 months. There is a magnetic 2D fitting on same circuit only a few feet from it, so maybe it's the cause of it failing.
Measured voltage this afternoon all seems ok to me,
L1-N= 240v. L1-E=241v. L1-L2=421v
L2-N=242v. L2-E=242v. L1-L3=417v
L3-N=245v. L3-E=245v. L2-L3=420v
All other tests were ok, no voltage between earth and neutral, think it's down to ballasts.
If anyone can think of anything else let me know thanks.