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Posted By Topic: Fluros burning out switches

Dec 14 2018 11:19

There is a bank of fluros which keep burning out the light switch, the mech is 20a rated, the lights are drawing less than 5amps (this was with a digital clamp meter so I may missed a spike).

Apparently the previous sparky just replaced the switch every year.

I was thinking of switching them through a contactor, but before I do that is there anything else I should look for that could be causing the switches to fail.

Dec 14 2018 11:45

Our firm has replaced heaps of PDL 20amp mechs over the last couple of years, some only switching 2 fluoro's in a garage. Often we now install a 32A mech to be safe.

PDL gear really has turned to custard.

Dec 14 2018 12:55

Ahh, it is a PDL 600 series mech

Dec 14 2018 13:04

The 20 A rating on PDL 500 / 600 switch mechs was only ever for resistive loads. The rating for fluos is 16 A. And you could well have harmonics in the system, which will stuff things up further.

I used to look after a factory where compressors for blast freezers etc had a FLC of 29 A, supplied on 16 mm2 conduit wire from 63A HRC fuses via contactor / overload sets. Fuse links 40 M 100, to cope with starting. Had repeated burn-outs of the (tunnel)terminals of the fuse holders; but never at the contactor (clamp) terminals. Over several years, probably changed every fuse connection, some more than once. That's the sort of thing that harmonics can do.

With switch-mode power supplies everywhere (including drivers for LEDs, CFLs, etc) we can't afford to ignore the issue like in the old days. And unless filters are fitted, they'll get out into the network and into other installations that may or may not be generating harmonics of their own. So not fair to just knee-jerk blame the fitting without bothering to find out what's actually going on in the circuit.

Dec 14 2018 13:20

Any idea what to look for? The brain isn't thinking too well at this time of year

Dec 14 2018 14:21

It is more likely the power factor of the SMPS in the LED driver is giving an leading factor factor and is trying tom correct the overall power factor of the whole installation.

There is not a lot able to be done other than using switches with a good current rating or only fitting a limited number of LED fittings or lamps on a common switch.


Dec 14 2018 19:54

They are fluro troffers, not LED's

Dec 14 2018 20:01

Are they electronic control gear by any chance?
These can have huge inrush currents. Have a read of the attached link. This can also affect LED’s.

Dec 15 2018 14:07

SMPS usually use a large capacitor across the mains input.

If a crude SMPS is being used (and most CFL lamps and cheap LED drivers and many cheap SMPS are of this class) the in rush current to charge the capacitor on each cycle can be up to 3 to 5 times the RMS running current and is usally a narrow spike of current so this spike is likely to be current damaging or detroying the switch contacts.

If a high specification SMPS is being used (often at high cost)the current spike is reduced or controlled and the current spike is considerably reduced.

It is case of you get what you pay for, buy cheap and get a poor specification SMPS.

For high specification they will generally be less operational problems.

Dec 15 2018 17:10

PDL switch mechs (20a standard) have a '16X' rating for fluorescent lamps.

Clipsal 30USM (Universal) mechs have a 16AX rating.

You could try a PDL 32a (unlabeled) switch mech.